JP2006253635A - Surface-emitting semiconductor laser device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-emitting semiconductor laser device with high efficiency and reliability in which sufficiently satisfying current constriction is achieved, and high external differential quantum efficiency is obtained with low threshold current. <P>SOLUTION: A surface-emitting semiconductor device has: insulation layers 107 and 108 embedding separation grooves for partially separating a waveguide path in an optical resonator formed by a pair of reflecting mirrors, namely a distributed reflection type multilayer film mirror 104 and a dielectric multilayer film mirror 11; and a quantum well active layer 105. In the surface-emitting semiconductor device, if oscillation wavelength of an end surface-emitting semiconductor laser device which has the same semiconductor layer as that constituting the optical resonator is made λ<SB>G</SB>, the oscillation wavelength λ<SB>G</SB>is set at a short wavelength side by a difference in specified wavelength (the amount of gain offset) ▵λ<SB>EM</SB>to a desired oscillation wavelength λ<SB>EM</SB>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a structure and manufacturing method of a surface emitting semiconductor laser device that emits light in a direction perpendicular to a substrate. Furthermore, the present invention relates to a structure and manufacturing method of a surface emitting semiconductor laser device that can be used in a parallel optical information processing apparatus such as an image forming apparatus or an optical communication system.

  Conventionally, as a structure of a surface emitting semiconductor laser device, the 3rd volume of the 50th JSAP Scientific Lecture Proceedings p. 909 29a-ZG-7 (issued September 27, 1989) has been reported. FIG. 45 is a perspective view showing the light emitting portion. This semiconductor laser device is manufactured by the following process. An n-type AlGaAs / AlAs multilayer film 2203, an n-type AlGaAs cladding layer 2204, a p-type GaAs active layer 2205, and a p-type AlGaAs cladding layer 2206 are grown on an n-type GaAs substrate 2202, leaving a cylindrical region 2220. Etching is performed, and AlGaAs layers 2207, 2208, 2209, and 2210 are buried in the order of p-type, n-type, p-type, and p-type. Thereafter, a dielectric multilayer film 2211 is deposited on the p-type AlGaAs cap layer 2210 to form an n-type ohmic electrode 2201 and a p-type ohmic electrode 2212, thereby forming a surface emitting semiconductor laser device.

  However, in the conventional surface-emitting type semiconductor laser device shown in FIG. 45, pn junctions 2207 and 2208 are provided in the buried layer as means for preventing current from flowing in portions other than the active layer. However, it is difficult to obtain sufficient current confinement with this pn junction, and the reactive current cannot be completely suppressed. For this reason, it is difficult for the conventional technology to drive continuous oscillation at room temperature due to heat generation of the element. In this laser device, since the entire optical resonator is embedded with a material having a lower refractive index than that of the resonator, light is confined in the resonator, and the cross-sectional shape in the horizontal direction is formed on the substrate surface of the resonator. Even if it is changed, the light emission spot in the fundamental oscillation mode becomes point light emission with a diameter of about 2 μm. Further, in this laser device, when the two-dimensional array, which is a feature of the surface emitting semiconductor laser device, is performed, each element oscillates independently even if individual resonators are placed close to each other in the substrate surface. Therefore, the phases of the individual laser beams are not aligned, and the respective laser beams interfere with each other, so that it is difficult to obtain a stable laser beam having one light beam.

  FIG. 46 is a cross-sectional view showing the structure of another conventional surface emitting semiconductor laser device. This laser device includes an n-type distributed reflection (DBR) mirror 2402, an n-type cladding layer 2408, a quantum well active layer 2403, a p-type cladding layer 2409, and a p-type DBR mirror 2404 on an n-type GaAs single crystal substrate 2401. In addition, a p-type ohmic electrode 2405 is formed. In the drawing, a region 2406 shown by hatching has a structure in which a single crystal state is destroyed by implanting hydrogen ions to form a high resistance region, and the injection current is concentrated only in the oscillation region. An n-type ohmic electrode 2407 is formed on the lower surface of the substrate 2401. Light is emitted from a direction 2410 perpendicular to the substrate 2401.

  In the conventional surface-emitting type semiconductor laser device shown in FIG. 46, the injection current flows through the p-type DBR mirror 2404. In the p-type DBR mirror 2404, holes flow as carriers in the current. The effective mass of holes is about 10 times larger than that of electrons, and does not easily exceed the hetero barrier inside the mirror. Therefore, the p-type DBR mirror 2404 has a large resistance component. In this conventional example, in order to increase the reflectivity of the p-type DBR mirror 2404, it is necessary to increase the number of mirror layers, and as a result, the resistance of the p-type DBR mirror 2404 is considerably increased. .

  An object of the present invention is to provide a surface-emitting type semiconductor laser device that can obtain a sufficiently satisfactory current confinement, has a low threshold current, has high external differential quantum efficiency, and is highly efficient and highly reliable. Another object of the present invention is to provide a method for manufacturing such a semiconductor laser device.

The surface emitting semiconductor laser device of the present invention is
A substrate made of a compound semiconductor of the first conductivity type,
A lower electrode formed on the lower side of the substrate;
A first reflection type distributed reflection multilayer mirror formed on the substrate;
A first conductivity type first cladding layer formed on the distributed reflection type multilayer mirror;
A quantum well active layer formed on the first cladding layer;
A second cladding layer of a second conductivity type formed on the quantum well active layer and having one or more columnar parts;
A second conductivity type contact layer formed on the columnar portion of the second cladding layer;
A buried insulating layer embedded around the columnar portion of the second cladding layer and the contact layer, and at least an interface between the second cladding layer and the contact layer is covered with a first insulating layer made of a silicon compound;
An upper electrode having an opening facing a portion of the contact layer and formed over both the contact layer and the buried insulating layer; and
A dielectric multilayer mirror formed on at least the contact layer so as to cover the opening of the upper electrode;

  In this semiconductor laser device, an optical resonator includes the distributed reflection type multilayer mirror, the first cladding layer, the quantum well active layer, the columnar portion of the second cladding layer, the contact layer, and the dielectric multilayer mirror. Is configured.

  In this semiconductor laser device, when a plurality of the columnar portions (resonator portions) are formed, the parallel transverse modes generated in the resonator portions are coupled to each other electromagnetically. Light whose phase is synchronized is oscillated from the container.

  The buried insulating layer has at least a first insulating film formed continuously along the surfaces of the cladding layer and the contact layer, and preferably, the second cladding layer is provided around the first insulating layer. A second insulating layer for flattening the periphery of the columnar portion and the contact layer is formed. The second insulating layer is preferably made of a material that can be formed at a lower temperature than the first insulating layer. The first insulating layer prevents impurities in the second insulating layer, such as sodium, chlorine, heavy metal, and hydrogen, from moving to the second cladding layer or the quantum well active layer by thermal diffusion or the like. This first insulating layer is preferably formed by thermal CVD (chemical vapor deposition). Therefore, it is desirable to reduce the time during which the optical resonator is exposed to heat at the time of film formation by reducing the thickness of the first insulating layer, thereby reducing damage to the crystal due to heat.

  As described above, the first insulating layer only needs to have a thickness sufficient to prevent the movement of a substance that adversely affects the optical resonator. For example, the thickness of the first insulating layer is set to 500 to 2000 angstroms. It is preferable. The first insulating layer is preferably composed of at least one silicon compound selected from, for example, a silicon oxide film, a silicon nitride film, and a silicon carbide film. The second insulating layer is preferably at least one selected from a silicon compound formed at a lower temperature than the silicon compound, a heat resistant resin such as polyimide, and a polycrystalline II-VI compound semiconductor. .

  In the second cladding layer, regions other than the columnar portions are removed by etching. The regions other than the columnar portions have a predetermined thickness, and preferably 0 μm (that is, completely removed) to 0.58 μm. More preferably, the film thickness is set to 0 to 0.35 μm. In this way, by making the film thickness of the region other than the columnar part a very thin film or completely removing it, current can be effectively injected into the active layer, and high external differential quantum efficiency can be obtained. Can do.

The quantum well active layer includes an n-type GaAs well layer and an n-type Al _0.3 Ga _0.7 As barrier layer. The well layer has a thickness of 40 to 120 Å, and the barrier layer has a thickness of 40 to It is preferably 100 angstroms and the total number of well layers is 3 to 40 layers. According to the quantum well active layer having such a configuration, it is possible to reduce the threshold value, increase the output, improve the temperature characteristics, and improve the reproducibility of the oscillation wavelength of the surface emitting semiconductor laser device.

The distributed reflection type multilayer mirror has at least 40nm or more reflectivity 99.2% in the wavelength range including the oscillation wavelength lambda _EM, the oscillation wavelength is set within the wavelength range. The reflectance of the distributed reflection type multilayer mirror also varies depending on the doping amount of each layer of the semiconductor layer constituting the mirror. For example, when a distributed reflection type multilayer mirror is formed by alternately laminating Al _0.8 Ga _0.2 As layers and Al _0.15 Ga _0.85 As layers, these layers are doped. The n-type dopant is preferably an average doping amount of 5 × 10 ¹⁶ to 1 × 10 ¹⁹ cm ⁻³ . Furthermore, the distributed reflection type multilayer mirror includes an Al _0.8 Ga _0.2 As layer having a high aluminum concentration, and an Al _0.15 Ga _0.85 As having a lower aluminum concentration and a larger band gap than this layer. It is desirable that the carrier concentration in the vicinity of the interface with the layer be higher than that in the region other than the vicinity of the interface. Specifically, it is preferable that the maximum value of the doping amount in the vicinity of the interface is 1.1 to 100 times the minimum value of the doping amount other than in the vicinity of the interface.

The dielectric multilayer mirror preferably has a reflectance of 98.5 to 99.5%. If the reflectance is lower than 98.5%, the oscillation threshold current increases. On the other hand, if the reflectance is higher than 99.5%, it is difficult to extract the light output to the outside, and the external differential quantum efficiency is lowered. Further, as the material constituting the dielectric multilayer mirror, it is preferable to use a material having a small light absorption loss with respect to the laser oscillation wavelength. Specifically, the dielectric multilayer mirror is less than 100 cm ^{−1 with} respect to the oscillation wavelength. It is preferable to be made of a dielectric material having an absorption coefficient. Examples of such a dielectric include SiO _x , Ta ₂ O ₅ , ZrO _x , TiO _x , ZrTiO _x , MgF _x , CaF _x , BaF _x and AlF _x .

  The columnar portion of the cladding layer constitutes an optical resonator, the diameter thereof is Da, the diameter of the opening of the upper electrode is Dw, Da is 6 to 12 μm, Dw is 4 to 8 μm, and Dw is It is preferable to form it slightly smaller than Da. The diameter of the columnar part (resonator diameter) and the diameter of the opening (outgoing aperture diameter) affect the transverse mode characteristics of the laser. In order to obtain fundamental transverse mode radiation, the resonator diameter must be set to a predetermined value. It is not preferable to make it larger than the size, and it is not preferable to make the diameter of the resonator too small in order to obtain a high output. From this point of view, in order to perform the fundamental transverse mode oscillation, it is preferable that Da and Dw are set in the above ranges.

The first cladding layer and the second cladding layer are made of a semiconductor layer represented by Al _x Ga 1 _-x As, where x is preferably 0.4 or more, more preferably 0.65 or more, and particularly preferably 0.7-0.8. By setting x within this range, the band cap of the cladding layer is sufficiently high, and the trapping of injected carriers into the active layer is good, and high external derivative quantum efficiency can be obtained.

  Furthermore, it is preferable that the columnar part of the second cladding layer has a thickness of 0.8 to 3.5 μm. When the film thickness is smaller than 0.8 μm, the injected carriers become non-uniform, especially a large amount of carriers are distributed near the periphery of the columnar portion, and carrier recombination that does not contribute to laser oscillation occurs, resulting in resonance. Since the carrier density in the vicinity of the center of the chamber is not sufficiently large, the optical output may be thermally saturated before reaching the laser oscillation threshold. On the other hand, if the film thickness is larger than 3.5 μm, the element resistance increases, leading to an increase in power consumption, and there is a possibility that thermal saturation of the optical output occurs at a low injection current.

Another surface emitting semiconductor laser device of the present invention is
A substrate made of a compound semiconductor of the first conductivity type,
A lower electrode formed on the lower side of the substrate;
A first reflection type distributed reflection multilayer mirror formed on the substrate;
A first conductivity type first cladding layer formed on the distributed reflection type multilayer mirror;
A quantum well active layer formed on the first cladding layer;
A second cladding layer of a second conductivity type formed on the quantum well active layer and having one or more columnar parts;
A second conductivity type contact layer formed on the columnar portion of the second cladding layer;
A buried insulating layer buried around the columnar portion of the second cladding layer and the contact layer;
An upper electrode having an opening facing a portion of the contact layer and formed over both the contact layer and the buried insulating layer; and
A dielectric multilayer mirror formed on at least the contact layer so as to cover the opening of the upper electrode,
The peak wavelength λ _G of the gain spectrum of the quantum well active layer is set to the short wavelength side by a predetermined wavelength difference (gain offset amount) Δλ _{BS with} respect to the intended oscillation wavelength λ _EM .

What is particularly characteristic in this semiconductor device is that the peak wavelength λ _G of the gain spectrum in the active layer is located on the short wavelength side by a gain offset amount Δλ _{BS with} respect to the oscillation wavelength λ _{EM of the} surface emitting semiconductor laser device. It is in the point formed as follows. The peak wavelength λ _G of the gain spectrum is, for example, an edge-emitting semiconductor laser device having the same semiconductor layer as the semiconductor layer formed on the substrate, which constitutes the surface-emitting semiconductor laser device of the present invention. It is determined by obtaining the oscillation wavelength of the edge emitting semiconductor laser device. The oscillation wavelength of the edge emission type semiconductor laser device is approximately equal to the peak wavelength lambda _G. The gain offset amount Δλ _BS is preferably 5 to 20 nm, more preferably 5 to 15 nm, and most preferably 10 to 15 nm. By setting such a gain offset amount, even if the peak wavelength of the gain spectrum of the active layer shifts to the longer wavelength side due to temperature rise, the oscillation wavelength and the peak wavelength of the gain spectrum specified by the resonator length Can be substantially matched with each other, and reliable laser oscillation can be performed with high efficiency.

More specifically, when the peak of the gain spectrum of the edge-emitting semiconductor laser device exists on the longer wavelength side than the oscillation wavelength of the surface-emitting semiconductor laser device, the peak wavelength of the gain spectrum is shifted to the longer wavelength side by current injection. As a result, the gain necessary for laser oscillation is reduced, and high output oscillation becomes difficult. However, the the gain offset amount is too large, even as the peak wavelength of the gain spectrum by current injection is shifted to the long wavelength side, there is a possibility that the gain at the oscillation wavelength lambda _EM does not cause too small lasing. For example, if the gain offset amount Δλ _BS exceeds 20 nm, continuous driving with a practical threshold current becomes difficult. On the other hand, if the gain offset amount Δλ _BS is smaller than 5 nm, the peak wavelength of the gain spectrum oscillates due to current injection. shifts from the longer wavelength side wavelength lambda _EM to become small gain at the oscillation wavelength, sufficient laser oscillation is not performed. Since the peak wavelength λ _G is temperature dependent, λ _G is measured at the temperature at which the surface emitting semiconductor laser device is used.

  In the semiconductor laser device in which the gain offset amount is set in this way, other configurations, specifically, the buried insulating layer, the second cladding layer, the quantum well active layer, the distributed reflection multilayer mirror, and The configuration of the dielectric multilayer mirror or the like preferably has the same configuration as the semiconductor laser device described above.

  Furthermore, in each surface-emitting type semiconductor laser device of the present invention, it is preferable to control the direction of the polarization plane of the laser light by specifying the shape of the columnar portion constituting the optical resonator. Hereinafter, this point will be described in detail.

  That is, it is preferable that the columnar portion constituting the resonator has a rectangular shape having a long side and a short side in a cross-sectional shape parallel to the semiconductor substrate. It has been experimentally confirmed that the direction of the polarization plane of the laser light is aligned in a direction parallel to the direction of the short side of the columnar portion having a rectangular cross section. Therefore, even when one resonator is formed in one element, or when a plurality of resonators are formed, each resonator indicates the direction of the polarization plane of the laser light emitted from each resonator. It can be aligned in the direction of the short side of the columnar part having a rectangular cross section.

  Then, when the length of the long side of the columnar section having a rectangular cross section is A and the length of the short side is B, it is preferable that B <A <2B. If A is 2B or more, the shape of the light exit is not a circle or a regular polygon, but a rectangle, so there is no single light emission spot, and multiple light emission spots are formed at one exit. End up. Further, since the volume of the resonator increases, the laser oscillation threshold current also increases.

  Further, it is preferable that a plurality of columnar portions of the second cladding layer are formed, and the directions of the short sides forming the rectangular cross section of each columnar portion are set in parallel. In this semiconductor laser device, the polarization planes of the laser beams emitted from the plurality of columnar portions coincide with the direction of the short side of each columnar portion having a rectangular cross section, and the direction of the short side of each columnar portion is Since they are parallel to each other, the phases of the laser beams emitted from one opening (light emission port) are synchronized and the directions of the polarization planes are also coincident. Therefore, for example, when this surface-emitting type semiconductor laser device is used in laser application equipment, the direction of the polarization plane of the laser light can be easily set to a specific direction without requiring fine position adjustment of each element. It becomes possible. Furthermore, in this semiconductor laser device, the buried insulating layer is made of a light-transmitting substance, so that the buried insulating layer becomes almost transparent with respect to the laser oscillation wavelength, and the light leaked from the buried insulating layer is also a laser. Since this contributes to the oscillation, the light emission spot is enlarged accordingly, the phase and the plane of polarization are aligned, and the light emission spot can emit one laser beam.

  The plurality of columnar portions having a rectangular cross section are arranged symmetrically on a two-dimensional plane parallel to the semiconductor substrate, and the shape of the opening formed in the upper electrode is a circle or a regular polygon. As a result, laser light having a substantially circular cross section can be emitted. Then, a plurality of such optical resonators constituted by the columnar portions are formed on the semiconductor substrate so as to independently have the upper electrode, and thereby laser light emitted from each optical resonator. The laser beam can be turned on, off, and modulated independently for each optical resonator.

  The plurality of optical resonators set the directions of the short sides of the rectangular cross section of the columnar part in parallel, thereby aligning the directions of the polarization planes of the laser beams emitted from the optical resonators in one direction. You can also In addition, by setting at least a part of the optical resonators to be parallel to the other optical resonators, the direction of the short side of the rectangular cross section of the columnar part is not parallel to at least a part of the optical resonators. The direction of the polarization plane of the emitted laser light may be different from the direction of the polarization plane of the laser light from the other optical resonator.

  Furthermore, the plurality of columnar portions having a rectangular cross section are arranged at equal intervals in rows and / or columns on a two-dimensional plane parallel to the semiconductor substrate, whereby the emitted laser beam is a line beam. It is also possible.

  The direction of the polarization plane of the laser light is parallel to the direction of the rectangular side of the light exit opening formed in the electrode on the light exit side, even if the columnar portion of the optical resonator does not have a rectangular cross section. Can be installed in the direction. This structure is effective when the columnar portions cannot be made rectangular due to restrictions on the arrangement of the columnar portions of the optical resonator on the two-dimensional surface. Moreover, it is good also considering both the cross-sectional shape of a columnar part, and the opening shape of a light-projection port as a rectangle. In this case, the direction of each rectangular side of the columnar part and the light exit port may be made parallel. When the length of the long side of the light exit port is a and the length of the short side is b, preferably b <a <2b. The reason for this is that if the ratio of b / a is increased, the ratio B / A of each side of the columnar portion of the optical resonator is increased accordingly, which is outside the preferred range of the lengths A and B of each side described above. Because it will end up.

  Various methods can be selected for the arrangement method of the optical resonators depending on the equipment to be applied. For example, when designing laser application equipment such as a laser printer, a measurement equipment using a laser beam, a laser pickup, and a laser communication equipment. A technique that can control the direction of the polarization plane of laser light is extremely useful.

  The surface-emitting type semiconductor laser device of the present invention is obtained, for example, by a manufacturing method including the following steps (a) to (e).

(A) On a substrate made of a first conductive type compound semiconductor, at least a first conductive type distributed reflection multilayer mirror, a first conductive type first cladding layer, a quantum well active layer, a second conductive type Forming a semiconductor layer including a second cladding layer and a second conductivity type contact layer by epitaxial growth;
(B) etching the contact layer and the second cladding layer to form one or more columnar portions;
(C) A step of forming a buried insulating layer around the columnar portion, and in this step, at least a first insulating layer made of a silicon compound covering an interface between the second cladding layer and the contact layer is formed. A step including a step of forming,
(D) forming an upper electrode facing the part of the contact layer and extending over both the contact layer and the buried insulating layer; and (e) opening the upper electrode. Forming a dielectric multilayer mirror on at least the contact layer so as to cover it;

  Another surface emitting semiconductor laser device of the present invention can be obtained by a manufacturing method including the following steps (a) to (e), for example.

(A) On a substrate made of a first conductive type compound semiconductor, at least a first conductive type distributed reflection multilayer mirror, a first conductive type first cladding layer, a quantum well active layer, a second conductive type Forming a semiconductor layer including a second cladding layer and a second conductivity type contact layer by epitaxial growth;
(B) etching the contact layer and the second cladding layer to form one or more columnar portions;
(C ′) forming a buried insulating layer around the columnar part;
(D) forming an upper electrode having an opening facing a part of the contact layer and extending over both the contact layer and the buried insulating layer; and (e) an opening of the upper electrode. Forming a dielectric multilayer mirror on at least the contact layer so as to cover,
The semiconductor layer is set so that the peak wavelength λ _G of the gain spectrum of the quantum well active layer is shorter than the intended oscillation wavelength λ _EM by a predetermined wavelength difference (gain offset amount) Δλ _BS. The The gain offset amount Δλ _BS is preferably set to 5 to 20 nm. Further, since the peak wavelength λ _G has temperature dependence, λ _G is measured at a temperature at which the surface emitting semiconductor laser device is used.

  The step (c ′) preferably includes a step of forming a first insulating layer made of a silicon compound that covers at least the interface between the second cladding layer and the contact layer.

  In each of the manufacturing methods, the buried insulating layer is formed by forming the first insulating layer by, for example, a thermal CVD method, and then forming a columnar portion of the second cladding layer and the periphery of the contact layer on the first insulating layer. A second insulating layer for planarization is preferably formed.

  The distributed reflection type multilayer mirror irradiates the semiconductor layer formed on the substrate by irradiating the substrate with light having a predetermined wavelength, for example, light having the same wavelength as the oscillation wavelength, and detecting the reflection spectrum. By measuring the reflectance profile and switching from the deposition of one semiconductor layer, which has a different refractive index at the maximum or minimum point of this reflectance profile, to the deposition of the other semiconductor layer, the low refractive index semiconductor layer and the high refractive index It is desirable that the semiconductor layers are alternately stacked.

  The reflectance profile does not depend on the crystal growth rate or growth time, but depends on the thickness of each layer and the refractive index of each layer. Therefore, by changing the Al composition of the layer to be laminated at the maximum or minimum point of the reflectance profile and alternately epitaxially growing layers having different refractive indexes, each layer has a theoretical thickness. Further, by selecting a semiconductor laser having a predetermined oscillation wavelength as a light source of input light for measuring the reflectance, the predetermined wavelength can be set strictly, so that the refractive index can also be obtained from the film thickness of each layer. Since the reflectance of the distributed reflection multilayer mirror itself can be measured during crystal growth, the number of mirror pairs can be changed during the layer formation, and the structure can be optimized.

  In each of the steps (b), during the etching, the substrate having the semiconductor layer is irradiated with light having a wavelength in a predetermined range, for example, a wavelength of ± 60 nm with respect to the oscillation wavelength, and the reflection spectrum is detected. It is desirable to control the etching thickness by measuring the dip due to the standing wave of the optical resonator that appears in FIG. The etching thickness is preferably controlled so that the film thickness of the region other than the columnar portion of the second cladding layer is within a predetermined range, for example, a range of 0 to 0.58 μm. The reason why this film thickness is preferable has already been described.

  In this way, when light is incident from the outside, the active layer absorbs light at a wavelength where a standing wave (longitudinal mode) exists in the semiconductor layer laminated on the distributed reflection type multilayer mirror. The reflectivity of the liquid crystal decreases, and a dip is formed in the reflection spectrum. Then, this dip moves from the long wavelength side to the short wavelength side corresponding to the decrease in the film thickness of the upper crystal layer from the distributed reflection type multilayer mirror, and when the etching is further continued, a new wavelength is again displayed on the long wavelength side. A dip occurs, and the movement and generation of the dip are repeated. Therefore, the etching amount and the etching rate can be managed by measuring the number of dips and the wavelength shift amount existing in the high reflectance band during etching. Therefore, a resonator in which the remaining film thickness in the region other than the columnar part is accurately controlled can be manufactured. In the etching step, the substrate temperature is preferably set to a predetermined temperature selected from 0 to 40 ° C.

  In addition, since the value and shape of the reflection spectrum can be monitored simultaneously during etching, surface contamination and damage during etching can be evaluated, and the evaluation results can be fed back to the etching conditions.

Furthermore, it is desirable that a protective layer made of SiO _x is formed on the surface of the semiconductor layer after the step (a). By covering the surface of the semiconductor on which this protective layer is laminated, surface contamination in a later process is prevented. Then, the protective layer is removed by, for example, reactive ion etching before the step (d). At that time, the substrate on which the protective layer is formed is irradiated with light having a predetermined wavelength, and the reflection spectrum is obtained. It is desirable to control the etching thickness of this protective layer by detecting and measuring its reflectance profile.

  In other words, the reflectivity changes depending on the remaining film thickness of the protective layer, and takes a maximum or minimum every time the remaining film thickness becomes an integral multiple of (λ / 4n), and the reflectivity changes when the protective layer is completely etched. Disappears. Here, λ is the wavelength of the measurement light source, and n is the refractive index of the protective layer. Therefore, the protective layer can be etched accurately and completely by measuring the reflectance during etching and monitoring the maximum and minimum points of the reflectance profile.

  Further, following the removal of the protective layer, the semiconductor layer formed in the step (a) is etched as necessary to control the resonator length. At the time of this etching, the substrate having the semiconductor layer is irradiated with light having a wavelength in a predetermined range, its reflection spectrum is detected, and the dip caused by the standing wave of the optical resonator appearing in this reflection spectrum is measured. Therefore, it is desirable to control the etching thickness. The mechanism is the same as in step (b). Further, the etching for controlling the resonator length may be performed immediately after the step (a). When etching is performed immediately after the step (a), there is an advantage that a wide range of epitaxial layers can be etched at once. Even during this etching, the mechanism of step (b) is used to control the etching thickness.

  In the step (a), the semiconductor layer is preferably formed by metal organic chemical vapor deposition.

  As an apparatus for manufacturing the surface emitting semiconductor laser device of the present invention, the following film forming apparatus and etching apparatus can be used.

For example, a film forming apparatus that forms a semiconductor layer on the substrate includes:
A reaction tube having a gas supply section and a gas discharge section;
A temperature-controllable substrate support installed inside the reaction tube;
A light source for irradiating the substrate support part with light of a predetermined wavelength;
A photodetector for detecting reflected light of light emitted from the light source to the substrate on the substrate support,
While the semiconductor layer is formed by epitaxial growth on the substrate placed on the substrate support portion, the reflectance of the semiconductor layer generated at the same time can be measured.

  According to this film forming apparatus, as described above, for example, the film thickness and resonator length of the distributed reflection type multilayer mirror can be set very accurately. A film forming apparatus capable of controlling the film thickness while monitoring the reflectance of the layer as described above can be applied not only to a metal organic vapor phase epitaxy apparatus but also to a molecular beam epitaxy apparatus.

Moreover, the etching apparatus used in the step (b) of forming the columnar part and the step of etching the protective layer,
An etching chamber,
A substrate support disposed in the etching chamber;
A light source for irradiating light of a predetermined wavelength on the substrate support;
A photodetector for measuring reflected light emitted from the light source to the substrate on the substrate support,
The reflectance can be measured simultaneously while etching the deposited layer on the substrate.

  According to such an etching apparatus, as described above, the etching amount can be accurately controlled by detecting the reflectance profile. The etching apparatus can be applied to reactive ion etching or reactive ion beam etching.

  The window used in the film forming apparatus and the etching apparatus is preferably non-reflective with respect to the light having the predetermined wavelength and the reflected light. These film forming apparatuses and etching apparatuses can employ various types of optical systems.

(First embodiment)
FIG. 1 is a perspective view schematically showing a cross section of a light emitting portion of a surface emitting semiconductor laser device according to an embodiment of the present invention.

A semiconductor laser device 100 shown in FIG. 1 has an n-type Al _0.8 Ga _0.2 As layer and an n-type Al _0.15 Ga _0.85 AS layer alternately stacked on an n-type GaAs substrate 102 and has a wavelength of 800 nm. 40 pairs of distributed reflection type multilayer mirrors (hereinafter referred to as “DBR mirrors”) 103 and n-type Al _0.7 Ga _0.3 AS layer having a reflectance of 99.5% or more with respect to the light in the vicinity A first cladding layer 104, an quantum well active layer 105 comprising an n ⁻ type GaAs well layer and an n ⁻ type Al _0.3 Ga _0.7 As barrier layer, the well layer comprising 21 layers (this embodiment) In this case, it is an active layer of a multiple quantum well structure (MQW)), a second cladding layer 106 made of a p-type Al _0.7 Ga _0.3 As layer, and a p ⁺ -type Al _0.15 Ga _0. contact consisting of a ₈₅ As layer 109, made by sequentially laminating. Then, part of the contact layer 109 and the second cladding layer 106 are etched into a circular shape when viewed from the upper surface of the semiconductor laminate, and the columnar portion 114 (hereinafter, this portion is referred to as a “resonator portion”. Resonator). The portion does not need to be cylindrical as will be described later.) The periphery of the first insulating layer 107 made of a silicon oxide film (SiO _x film) such as SiO ₂ formed by a thermal CVD method, polyimide, etc. It is embedded with a second insulating layer 108 made of heat resistant resin or the like.

  The first insulating layer 107 is formed continuously along the surfaces of the second cladding layer 106 and the contact layer 109, and the second insulating layer 108 is formed so as to embed the periphery of the first insulating layer 107. .

As the second insulating layer 108, in addition to the above-mentioned heat-resistant resin such as polyimide, a silicon oxide film (SiO _x film) such as SiO ₂ , a silicon nitride film (SiN _x film) such as Si ₃ N ₄ , SiC, etc. Insulating silicon compound film such as silicon carbide film (SiC _x film), SOG (SiO _x such as SiO ₂ by spin-on-glass method) film, or polycrystalline II-VI group compound semiconductor film (for example, ZnSe) may be used. . Among these insulating films, it is preferable to use a silicon oxide film such as SiO _{2 that} can be formed at a low temperature, polyimide, or SOG film. Furthermore, it is preferable to use an SOG film because the formation is simple and the surface is easily flattened.

Further, the contact metal layer (upper electrode) 112 made of, for example, Cr and Au—Zn alloy is formed in contact with the contact layer 109 in a ring shape, and serves as an electrode for current injection. A portion of the contact layer 109 not covered with the upper electrode 112 is exposed in a circular shape. Then, the exposed surface of the contact layer 109 (hereinafter, this portion referred to as "opening") at the area covering the sufficiently, in the vicinity of a wavelength of 800nm by stacking SiO _x and _Ta 2 _{O 5} layer of SiO ₂ or the like alternately Seven pairs of dielectric multilayer mirrors 111 having a reflectance of 98.5 to 99.5% with respect to light are formed. An electrode metal layer (lower electrode) 101 made of, for example, Ni and Au—Ge alloy is formed under the n-type GaAs substrate 102.

  FIG. 3 is a diagram showing a laser emitting portion viewed from the direction 110 in which the laser beam of the semiconductor laser device shown in FIG. 1 is emitted. The cross section taken along the line AA 'in FIG. 3 corresponds to the cross sectional view seen from the front in FIG. The upper electrode 112 is alloyed so as to come into contact with the contact layer 109 and make an ohmic contact. The dielectric multilayer mirror 111 is formed so as to cover the entire surface of the resonator unit 114. Here, as shown in FIG. 3, the diameter of the resonator unit 114 is expressed as Da and the diameter of the opening 113 is expressed as Dw.

  A forward voltage is applied between the upper electrode 112 and the lower electrode 101 (in this embodiment, a voltage is applied in the direction from the upper electrode 112 to the lower electrode 101). Done. The injected current is converted into light by the quantum well active layer 105, amplified by reciprocating the light between the reflecting mirrors constituted by the DBR mirror 103 and the dielectric multilayer mirror 111, and the opening 113. Laser light is emitted from the (exposed surface of the contact layer 109) in the direction 110, that is, in the direction perpendicular to the substrate 102.

Here, the first insulating layer 107 made of the silicon oxide film (SiO _x film) in FIG. 1 has a film thickness of 500 to 2000 angstroms and is formed by the atmospheric pressure thermal CVD method. The second insulating layer 108 made of heat resistant resin or the like is necessary for planarizing the surface of the element. For example, although heat-resistant resin has high resistance, moisture tends to remain in the film, and if it is in direct contact with the semiconductor layer, voids will form at the interface with the semiconductor when the element is energized for a long time. Occurs and deteriorates the characteristics of the element. Therefore, as in this embodiment, when a thin film such as the first insulating layer 107 is inserted into the boundary with the semiconductor layer, the first insulating layer 107 becomes a protective film and the above-described deterioration does not occur. There are various methods for forming a silicon oxide film (SiO _x film) constituting the first insulating layer, such as a plasma CVD method and a reactive vapor deposition method. SiH ₄ (monosilane) gas and O ₂ (oxygen) gas are used. A film forming method by atmospheric pressure CVD using N ₂ (nitrogen) gas as a carrier gas is most suitable. The reason is that the reaction is carried out at atmospheric pressure, and the film is formed under the condition that O ₂ is excessive, so that there is little oxygen deficiency in the SiO _x film, and the step coverage is good and resonance is achieved. The same thickness as that of the flat portion can be obtained on the side surface and the stepped portion of the vessel portion 114.

  Next, a manufacturing process of the surface emitting semiconductor laser 100 shown in FIG. 1 will be described. 22A to 22C and FIGS. 23D to 23F show the manufacturing process of the surface emitting semiconductor laser device.

As described above, the n-type Al _0.15 Ga _0.85 As layer and the n-type Al _0.8 Ga _0.2 As layer are alternately stacked on the n-type GaAs substrate 102 to obtain light having a wavelength of about 800 nm. On the other hand, 40 pairs of DBR mirrors 103 having a reflectance of 99.5% or more are formed. Further, after the n-type Al _0.7 Ga _0.3 As layer (first cladding layer) 104 is formed, the n − type GaAs well layer and the n − type Al _0.3 Ga _0.7 As barrier layer are alternately formed. An active layer 105 having a quantum well structure (MQW) is formed. Thereafter, a p-type Al _0.7 Ga _0.3 As layer (second cladding layer) 106 and a p-type Al _0.15 Ga _0.85 As layer (contact layer) 109 are sequentially stacked (see FIG. 22A).

Each of the above layers was epitaxially grown by a metal-organic vapor phase epitaxy (MOVPE) method. At this time, for example, the growth temperature is 750 ° C., the growth pressure is 150 Torr, an organic metal such as TMGa (trimethylgallium) or TMAl (trimethylaluminum) is used as the group III material, AsH ₃ is used as the group V material, and H is used as the n-type dopant. DEZn (diethyl zinc) was used for ₂ Se and p-type dopants.

As shown in FIG. 22A, after each layer is formed, a protective layer I composed of a SiO ₂ layer of about 250 angstroms is formed on the epitaxial layer by atmospheric pressure CVD. By covering the semiconductor layer on which the protective layer I is laminated, surface contamination during the process is prevented.

  Note that one of the wafers obtained by the above steps and having the DBR mirror 103, the first cladding layer 104, the quantum well active layer 105, the second cladding layer 106, the contact layer 109, and the insulating layer I formed on the substrate 102. The part is used as a sample of an edge-emitting semiconductor laser device to be described later.

  Next, etching is performed to the middle of the protective layer I, the contact layer 109 and the second cladding layer 106 by the reactive ion beam etching (RIBE) method, leaving the columnar resonator portion 114 covered with the resist pattern R1. By performing this etching process, the columnar portion constituting the resonator portion 114 has the same cross section as the contour shape of the resist pattern R1 thereon (see FIG. 22B). Further, since the RIBE method is used, the side surface of the columnar portion is almost vertical and there is almost no damage to the epitaxial layer. The RIBE conditions were, for example, a pressure of 60 mPa, an input microwave power of 150 W, an extraction voltage of 350 V, and a mixed gas of chlorine and argon was used as an etching gas.

  In the formation of the columnar portion by the RIBE method, the temperature of the substrate 102 is set to a relatively low temperature during etching, that is, preferably 0 to 40 ° C., more preferably 10 to 20 ° C. As described above, by maintaining the temperature of the substrate at a relatively low temperature, side etching of a semiconductor layer stacked by epitaxial growth can be suppressed. However, although it is preferable from the point of suppressing side etching that the temperature of the substrate is 0 to 10 ° C., it is not practically suitable because the etching rate becomes slow. Further, when the substrate temperature exceeds 40 ° C., the etching rate becomes too high, so that not only the etching surface is roughened, but also the etching rate is difficult to control.

Thereafter, the resist pattern R1 is removed, and an SiO ₂ layer (first insulating film) 107 of about 1000 angstroms is formed on the surface by atmospheric pressure CVD. As process conditions at this time, for example, substrate temperature was 450 ° C., SiH ₄ (monosilane) and oxygen were used as raw materials, and nitrogen was used as a carrier gas. Further, an SOG (Spin on Glass) film 108L is applied thereon by using a spin coating method, and then, for example, baking is performed in nitrogen at 80 ° C. for 1 minute, 150 ° C. for 2 minutes, and further at 300 ° C. for 30 minutes ( (See FIG. 22C).

Next, the SOG film 108L, the SiO ₂ film 107, and the protective layer I were etched back and planarized so as to be flush with the exposed surface of the contact layer 109 (see FIG. 23D). For the etching, a reactive ion etching (RIE) method using parallel plate electrodes was employed, and SF ₆ , CHF ₃ and Ar were used in combination as reaction gases.

Next, the upper electrode 112 in contact with the contact layer 109 in a ring shape was formed by a known lift-off method (see FIG. 23E). The contact layer 109 is exposed through the circular opening of the upper electrode 112, and a dielectric multilayer mirror (upper mirror) 111 is formed by a known lift-off method so as to sufficiently cover the exposed surface (see FIG. 23F). . The upper mirror 111 is formed by alternately stacking, for example, 7 pairs of SiO ₂ layers and Ta ₂ O ₅ layers using an electron beam evaporation method, and 98.5 to 99.5% with respect to light having a wavelength of about 800 nm. With a reflectivity of. The deposition speed at this time was, for example, 5 angstrom / min for SiO _{2 and 2} angstrom / min for the Ta ₂ O ₅ layer.

  The upper mirror 111 may be formed by an RIE method other than the lift-off method.

  Thereafter, the lower electrode 101 made of Ni and AuGe alloy is formed on the lower surface of the substrate 102, thereby completing the surface emitting semiconductor laser device.

  As described above, the components and the manufacturing process of the present embodiment have been described in general. The main structural features of the present embodiment are as follows.

(A) Quantum well active layer The quantum well active layer 105 includes an n ⁻ type GaAs well layer and an n ⁻ type Al _0.3 Ga _0.7 As barrier layer. In this embodiment, the active layer has a multiple quantum well structure (MQW). The thickness of the well layer is 40 to 120 angstroms, preferably 61 angstroms, the thickness of the barrier layer is 40 to 100 angstroms, preferably 86 angstroms, and the total number of well layers is 3 to 40 layers, preferably 21 layers. As a result, it is possible to reduce the threshold value, increase the output, improve the temperature characteristics, and improve the reproducibility of the oscillation wavelength of the surface emitting semiconductor laser device.

(B) Embedded insulating layer The embedded insulating layer includes a thin silicon oxide film (first insulating layer) 107 formed by a thermal CVD method and a second insulating layer embedded thereon (specific materials are: (See the above description) 108). In this structure, the reason why the thin first insulating layer 107 is formed is that the second insulating layer 108 to be formed thereafter contains a large amount of impurities (for example, sodium, chlorine, heavy metal, water, etc.). This is to prevent diffusion into the clad layer 106 or the quantum well active layer 105 by heat or the like. Therefore, the first insulating layer 107 may have a thickness that can prevent impurities. In addition, since the thin first insulating layer 107 is formed by thermal CVD, the film quality is dense compared to the second insulating layer 108 formed thereafter. In the present embodiment, since the first insulating layer 107 is formed by thermal CVD, the first insulating layer 107 is not thickened into one layer in consideration of the influence of heat on the element. A two-layer structure of a thin first insulating layer 107 and a second insulating layer 108 that can be formed at a lower temperature even if the film quality is not dense is employed.

  In this embodiment, the buried insulating layer does not reach the quantum well active layer 105, that is, in the region other than the resonator unit 114, between the first insulating layer 107 and the quantum well active layer 105, The second cladding layer 106 is also characterized by leaving a predetermined thickness (t). The remaining film thickness t is preferably set to 0 to 0.58 [mu] m, more preferably 0 to 0.35 [mu] m, for reasons to be described later. As a result, in the surface emitting semiconductor laser device, current is effectively injected into the active layer, and high efficiency and high reliability can be achieved.

(C) a dielectric multilayer mirror dielectric multilayer film mirror 111, by laminating a SiO _x layer and the _Ta 2 _{O 5} layer such as SiO ₂ alternately with respect to light near a wavelength of 800 nm from 98.5 to 99.5% Are formed from 7 pairs of dielectric multilayer films having a reflectivity of 5 nm. Instead, the Ta ₂ O ₅ layer may be composed of any one of a ZrO _x film, a ZrTiO _x film, and a TiO _x film. Alternatively, the SiO _x layer may be composed of any one of an MgF ₂ film, a CaF ₂ film, a BaF ₂ film, and an AlF ₂ film. As a result, the threshold value of the surface emitting semiconductor laser device can be lowered and the external differential quantum efficiency can be improved.

  This point will be described in more detail. A feature of the surface emitting semiconductor laser device of this embodiment is that a laser resonator is formed by using an n-type DBR mirror 103 and a dielectric multilayer mirror 111, and for example, a p-type DBR mirror shown in the prior art of FIG. It is not included. That is, this conventional example has a problem that the number of mirror layers needs to be increased in order to increase the reflectivity of the p-type DBR mirror, and the resistance of the p-type DBR mirror becomes very large. On the other hand, the embodiment of the present invention is characterized in that the dielectric multilayer mirror 111 is used without using the p-type DBR mirror. As a result, the following effects can be obtained.

  (1) In the apparatus of the present embodiment, the injected current flows through the contact layer 109 and the second cladding layer 106, and therefore does not have a large resistance.

That is, the series resistance of the device can be lowered, and the voltage at the threshold current value (I _th ) (hereinafter referred to as “threshold voltage” and expressed as “V _th ”) can be lowered. As a result, the heat generation of the device due to the injection current can be suppressed, and as a result, the external differential quantum efficiency can be increased and the light output capable of oscillation can be improved.

  (2) Since the dielectric multilayer mirror is formed after the crystal growth of the cladding layer, the active layer, etc., it is possible to manufacture a surface emitting semiconductor laser device in which the resonator length is accurately matched to the resonance conditions. The control of the resonator length will be described in detail later.

Next, FIG. 2 shows the relationship between the injection current and the optical output of the surface emitting semiconductor laser device of the embodiment shown in FIG. 1 of the present invention and the surface emitting semiconductor laser device of the conventional example shown in FIG. (Hereinafter referred to as “IL characteristics”) and characteristics indicating the relationship between the injection current and the forward voltage (hereinafter referred to as “IV characteristics”) are collectively shown. In FIG. 2, the curve shown by the solid line shows the IL characteristic 201 and the IV characteristic 202 of this embodiment, and the curve shown by the broken line shows the IL characteristic 203 and the IV characteristic 204 of the conventional example. ing. As is apparent from both IV characteristics, there is a large difference in device resistance. It can be seen that the device resistance of this example is smaller by one digit or more than that in the case of using the conventional p-type DBR mirror. In the conventional example, the device resistance is about 600Ω, whereas the device resistance of the present embodiment is about 50Ω. The threshold voltage V _th (voltage value of the IV characteristic with respect to the current value of I _th of the _IL characteristic) is about 4.0 V in the conventional example, and is about 1.9 V in this embodiment. It is a low value of 1/2 or less. As a result, the surface-emitting type semiconductor laser device of the present embodiment suppresses heat generation due to the injection current of the device, and an optical output is obtained without thermal saturation up to a high current region.

  Further, as apparent from the IL characteristic of FIG. 2, in the IL characteristic 203 of the conventional example, since the device resistance is high, the light output is saturated at about 6 mA due to the heat generated thereby, A light output of about 0.4 mW can be obtained. On the other hand, in the IL characteristic 201 of the present embodiment, an output of 1.2 mW is obtained without saturation of the optical output up to about 10 mA.

FIG. 4 is an IL characteristic diagram showing the relationship between the injection current and the optical output of the surface-emitting type semiconductor laser device in this example. The sample used for obtaining the IL characteristic is Dw = 6 μm (the portion where the laser light is emitted, that is, the diameter of the opening 113) in the surface emitting semiconductor laser device having the configuration shown in FIGS. Da = 8 μm (diameter of the resonator 114), the thickness of the GaAs well layer in the quantum well active layer 105 is 61 Å, the thickness of the Al _0.3 Ga _0.7 As barrier layer is 86 Å, and the oscillation wavelength Is 800 nm. A characteristic curve 401 is a result when the surface-emitting type semiconductor laser device having the above-described configuration is pulse-driven with a pulse current having a pulse width of 200 nsec and a repetition frequency of 10 kHz, and a characteristic curve 402 is a surface having the above-described configuration. The result when the light emitting semiconductor laser device is continuously driven by a direct current is shown. Both start laser oscillation with a clear threshold, and the threshold current in the case of continuous driving is as low as 2 mA. In the case of pulse driving, the external differential quantum efficiency after oscillation with a lower threshold current is higher than in the case of continuous driving. In the case of continuous driving, the influence of the temperature rise of the element due to the injected current is large, and it can be seen that the linearity of the IL characteristic deteriorates as the injected current is increased. In order to realize a practical surface-emitting laser device, it is important to obtain characteristics with a low threshold current value and a high external differential quantum efficiency, and as a result, to reduce the drive current value as much as possible.

  In the following, embodiments according to the present invention will be described in more detail, and how it is possible to reduce the drive current will be described with reference to FIGS. 5A and 5B. The surface emitting semiconductor laser device shown in FIG. 5A is a comparative device.

5A is different from the cross-sectional view seen from the front of FIG. 1 in that the buried insulating layer reaches the quantum well active layer 105. FIG. That is, in this figure, the contact layer 109, the second cladding layer 106, the quantum well active layer 105, and a part of the n-type cladding layer 104 are etched by a reactive ion beam etching method using chlorine ions, and the periphery thereof is silicon. FIG. 2 shows a cross-sectional structure of a surface emitting semiconductor laser device embedded with a first insulating layer 107 made of an oxide film (SiO _x film) and a second insulating layer made of polyimide.

FIG. 5B is structurally similar to the cross-sectional view seen from the front of FIG. That is, the etching does not reach the quantum well active layer 105 as shown in FIG. 5A but stops halfway through the second cladding layer 106 made of the p-type Al _0.5 Ga _0.5 As layer, and the periphery thereof is shown in FIG. 5A. FIG. 2 is a sectional view of a surface emitting semiconductor laser device embedded in the same manner as FIG. Then, as shown in FIG. 5B, the remaining etching thickness of the second cladding layer 106 is expressed as “t”.

  With the structure of FIG. 5A, what kind of problem occurs will be described below based on the experimental result of FIG.

601 straight line shown in in FIG. 6, divided by the threshold current density (the area of the resonator unit oscillation threshold current I _th of a surface emitting semiconductor laser device shown in FIG. 5A (diameter is Da) Value; expressed as “J _th ”) and 1 / πDa. In this case, the diameter Dw of the opening in the fixed and 6 [mu] m, the laser device changing only the diameter Da of the resonator portion and a plurality prepared, to measure the I _th, in which to determine the J _th. Cut a quantum well active layer 105 as in FIG. 5A, I _th if the side surface is in contact with the first insulating layer 107, the interface recombination current flows at the bonding surfaces, as a current whose components leak Increase. J _th is expressed by the following equation (1) when there is an interface recombination current.

Threshold current density here when J ₀ is no leakage current, e is electron charge amount, N _th is the threshold carrier density, d _a is the active layer thickness, v _s denotes the surface recombination velocity. When apparent in interface recombination current exists from the equation (1), J _th has a component proportional to the reciprocal of the diameter Da of the resonator portion, changes to higher interface recombination current is large (1 / Da) The rate is great. Interface recombination current is leakage current in the non-light emitting, which is as large as allowed rise to heating of the element to that which causes and current increase I _th, adverse effects that attenuate light emission efficiency.

On the other hand, the straight line 602 in FIG. 6 is the result of the same measurement for the surface emitting semiconductor laser device of this example having the structure shown in FIG. 5B. As is apparent from FIG. 6, when etching does not proceed to the quantum well active layer 105 of FIG. 5B, that is, when there is no interface between the quantum well active layer and the buried insulating layer, J _th is (1 / Da). And the threshold current value also decreases. Therefore, when forming the resonator part, it is particularly important in terms of the structure of the surface emitting semiconductor laser device to provide the remaining film thickness t in the second cladding layer 106 and eliminate the interface recombination current. I understand.

However, the remaining film thickness t of the second clad layer 106, increases the spread of the injected carriers too thick leads to an increase of the I _th. Therefore, it is necessary to stop the etching at an appropriate thickness, and it is most preferable that the etching is finished at the boundary with the quantum well active layer 105, that is, the remaining film thickness t = 0 of the second cladding layer. . Although this may be difficult in terms of manufacturing technology, there is no problem in theory. That is, the active layer underneath is not substantially etched.

FIG. 7 collectively shows IL characteristics of a plurality of surface-emitting type semiconductor laser devices having different thicknesses t after etching of the second cladding layer 106 in the embodiment of the present invention. In obtaining the IL characteristics, the resonator portion 114 has a diameter Da of 8 μm, the opening 113 has a diameter Dw of 6 μm, the quantum well active layer 105 has 21 quantum wells, and the remaining film thickness t is determined as follows. A plurality of elements (oscillation wavelength: 800 nm) were produced by changing, and measured under the condition of continuous driving. As is apparent from FIG. 7, when t is larger than 0.62 μm, I _th becomes 10 mA or more, the external differential quantum efficiency is lowered, and the light output immediately causes thermal saturation.

  Further, a preferable numerical range of the remaining film thickness t of the cladding layer will be described with reference to FIG.

  In FIG. 8, the vertical axis represents the value of slope (slope efficiency) indicating the external differential quantum efficiency, and the horizontal axis represents the remaining film thickness t of the cladding layer. When the slope efficiency is 0.1 (that is, 10%), only a light output of 1 mW can be obtained even with a current of 10 mA. Generally, this current value of 10 mA is a current value close to the current value at which the laser element is thermally saturated, and is almost close to the limit. Therefore, the slope required for practical use is 0.1 or more, and the remaining film thickness t when the slope efficiency is 0.1 is about 0.58 μm from FIG. 0 to 0.58 μm. Furthermore, since the light output required when the surface emitting semiconductor laser device is used for, for example, a printer is preferably 2 mW, more preferably 2.5 mw, the preferable remaining film thickness t is preferably 0 to 0.4 μm, more preferably Is 0 to 0.3 μm.

  It has been briefly described above that the characteristic component of the present invention is the structure of the quantum well active layer 105. This will now be described in detail with reference to FIG.

FIG. 9 is a diagram showing a measurement result of an emission spectrum by photoexcitation from a single quantum well structure grown by the MOVPE method in one example of the present invention. In the sample, single quantum well layers having different thicknesses are grown on a GaAs single crystal substrate through an Al _0.3 Ga _0.7 As barrier layer having a thickness of 500 Å. The measurement was performed by cooling the sample to a liquid nitrogen temperature (77 K), irradiating with 300 mW argon laser light, and spectrally resolving the emitted light with a spectroscope. The thinner the quantum well, the higher the energy level, and a sharp emission spectrum was observed at short wavelengths. FIG. 9 shows the peak wavelength of light emission corresponding to each quantum well film thickness (17, 33, 55, 115 angstroms from the left peak in the figure) and its half width (also 8.3, 9.6, 7). .8, 5.6 meV).

  Further, a solid line 1001 in FIG. 10 is a result obtained by theoretically calculating the relationship between the quantum well film thickness (horizontal axis) and the corresponding peak wavelength (vertical axis), and the dot (●) indicates the measurement result in FIG. Are plotted. From this figure, the measured values and the theoretical calculations are almost the same, and it can be seen that the quantum well structure is fabricated in a form close to the theory.

  FIG. 11 shows the relationship between the half-value width of the emission intensity from the quantum well and the quantum well width as a theoretically obtained result and a measurement result. The broken line 1101 in FIG. 11 is a theoretically calculated half width, and the broken line 1102 indicates how much the half width with respect to the well width is when the quantum well width has an unevenness of one atomic layer. The result of theoretically calculating whether it spreads is shown. In addition, a solid line and a dot (●) of 1103 indicate actual measurement values. Thus, as is apparent from FIG. 11, it can be seen that in this embodiment, the half width is sufficiently narrower than that in the case where there is a fluctuation of one atomic layer, and an ideal quantum well is formed.

  In order to make such a quantum well structure having no fluctuation of one atomic layer, it can be manufactured by devising and using a crystal growth apparatus of the MOVPE method.

  As described above, when a single quantum well can be produced, it is possible to produce a multiple quantum well by successively laminating them. In the quantum well active layer of the surface emitting semiconductor laser device, in order for light amplification to occur, it is necessary that the injected carriers are confined in the active layer and the injected carriers are distributed in the quantum well layer.

Further, in order to achieve a low threshold current in the structure of the surface emitting semiconductor laser device, it is necessary to optimize the thickness of the active layer in consideration of the standing wave inside the resonator. FIG. 12 shows a theoretical calculation of the change in the threshold current density (J _th ) of the surface emitting semiconductor laser device with respect to the total thickness of the active layer. FIG 12, Rr the reflectance of the DBR mirror 103 in FIG. 1, the reflectance of the dielectric multilayer film mirror 111 and _{R f,} Fabry-Perot is made of a mirror 103 and 111 - average reflectance _{R m} of the resonator This shows a case where (= (R _r · R _f ) ^1/2 ) is changed. _Jth is represented by the following formula (2).

Here, e is the charge amount of electrons, d is the thickness of the active layer, L is the length of the resonator, ξ is the light confinement factor, α _ac is the optical loss of the active layer, and α _in is the carrier is not injected. Loss in the state, α _ex represents the loss of the resonator part other than the active layer, and A ₀ represents a constant. FIG. 12 shows the relationship between the total thickness of the active layer and the threshold current density based on the above theoretical formula. The solid line indicates the standing wave distribution when the standing wave distribution in the resonator is not considered. It is a calculation result when the wave distribution is taken into consideration. In Figure 12, the average reflectance _{R m} represents the results when the 0.98,0.99,0.995, ● terms of the case of the film thickness of the active layer is 0.13 [mu] m, Rm 0.98 Measured values of the light emitting laser, and ▪ indicate measured values when the thickness of the active layer is 0.29 μm and Rm is 0.99. Each measured value is in good agreement with the theoretical value. By making this active layer a quantum well structure, the threshold current was further reduced, and I _th = 2 mA was actually obtained when D _a = 8 μm.

  As described above, the following two points are necessary as conditions for the active layer necessary to achieve a lower threshold of the surface emitting semiconductor laser device.

  (1) The active layer has a quantum well structure, which is a steep well having a flatness (unevenness) of a single atom or less.

  (2) A value at which the total thickness of the quantum well active layer takes a minimum value of the threshold current density in consideration of the standing wave distribution in the resonator, for example, a range of 0.27 to 0.33 μm or 0.65 to 0 It should be set in the range of .75 μm (see FIG. 12).

Since the film thickness of the quantum well is set by the oscillation wavelength of laser oscillation, the total film thickness is controlled by repeatedly forming quantum wells and changing the number of wells. For example, when manufacturing a surface emitting semiconductor laser device that oscillates at an oscillation wavelength of 800 nm, the quantum well layer is GaAs and the film thickness is 61 angstroms, and the barrier layer is Al _0.3 Ga _0.7 As and the film thickness is 86 angstroms. 21 pairs of multiple quantum well structures may be formed.

  Next, the number of well layers in the active layer will be described with reference to FIG.

  FIG. 47 shows the influence of the number of well layers on the IL characteristic. That is, the curves a to h in FIG. 47 indicate I when the number of well layers of the active layer having a predetermined film thickness (da) is 1, 2, 3, 12, 21, 30, 40, and 50, respectively. -L characteristic is shown. The film thickness (da) satisfies the conditions shown in FIG. The thickness of the active layer indicated by curves a to e is 0.3 μm, and the thickness of the active layer indicated by curves f to h is 0.7 μm.

  The total film thickness of the well layer in the active layer varies depending on the number, but the film thickness of the active layer can be set to a predetermined value by controlling the total film thickness of the barrier layer. For example, when the barrier layers cannot be formed at a predetermined thickness and at equal intervals, the outermost barrier layers B1 and B2 are formed with the thicknesses of the other barrier layers as shown in FIG. By making it larger than the thickness, the thickness of the entire active layer can be defined.

  FIG. 47 shows that it is effective to reduce the number of well layers in order to reduce the threshold current, and to increase the number of well layers in order to increase the light output. That is, in order to perform laser oscillation, the number of well layers must be 1 to 40, and the number of well layers must be 3 to 30 in order to obtain an optical output of 1 mW or more. Therefore, the appropriate number of well layers in this embodiment is 3-30.

Next, the influence of the band gap size of the cladding layer on the laser oscillation characteristics will be described in detail. FIG. 13 shows the Al composition of each growth layer Al _x Ga 1 _-x As of a surface emitting semiconductor laser device wafer crystal-grown on a GaAs single crystal substrate. Since AlGaAs has a larger band gap as the Al composition ratio is higher, FIG. 13 also shows how the band gap changes. Carriers injected into the active layer are confined by the band gap of the clad layer, and the better the carrier confinement, the better the temperature characteristics of the device. A surface emitting semiconductor laser device in which the Al composition x of the n-type cladding layer and the second cladding layer in FIG. 13 is 0.5 and a surface emitting semiconductor laser device in which x is 0.7 are manufactured. I compared the characteristics. The sample was fabricated under exactly the same conditions except for the composition of the cladding layer, and the quantum well active layer was composed of a quantum well layer having a GaAs thickness of 61 Å and a barrier layer having a thickness of Al _0.3 Ga _0.7 As and a thickness of 86 Å. a multiple quantum well structure 21 pairs superposed dielectric multilayer film mirror has a reflectivity of 99.0% at a wavelength of SiO _x and _Ta 2 _{O 5} and 8 pairs laminated to 800 nm, _{D a} is 8 [mu] m, _{D w} Is 6 μm.

  FIG. 14 is a diagram showing IL characteristics of two types of surface-emitting type semiconductor laser devices. In the figure, a curve 1401 shows the characteristics of a surface emitting semiconductor laser device in which the first and second cladding layers have an Al composition of 0.5, and a curve 1402 shows a surface emitting type in which the first and second cladding layers have an Al composition of 0.7. The characteristics of the semiconductor laser device are shown. In both cases, current flows under the condition of continuous driving at room temperature. As apparent from FIG. 14, the external differential quantum efficiency is higher when the Al composition of the clad layer is larger, and it is possible to extract a laser beam output that is twice or more. This indicates that confinement of injected carriers in the active layer works effectively by the potential barrier of the cladding layer.

  Further, the Al composition of the cladding layer will be described with reference to FIG. In FIG. 15, the vertical axis represents a value (slope efficiency) representing external differential quantum efficiency (slope of IL characteristics), and the horizontal axis represents the Al composition in the cladding layer. As described with reference to FIG. 8, the external differential quantum efficiency usually needs to be 0.1 or more. Therefore, the Al composition of the cladding layer is preferably 0.4 or more. When the surface emitting semiconductor laser device is used for a printer, the necessary light output is 2 mW or more, and therefore the preferable Al composition of the cladding layer is 0.65 or more, and more preferably 0.7 to 0. .8 or so.

  Next, conditions necessary for achieving further lowering of the threshold will be described in detail. The dielectric multilayer mirror 111 in FIG. 1 needs to have a reflectance of 98.5 to 99.5% with respect to the laser oscillation wavelength. If the reflectivity is lower than 98.5%, the oscillation threshold current increases significantly as is apparent from the theoretical calculation of FIG. On the contrary, if it is larger than 99.5%, it is difficult to take out the light output to the outside, and the external differential quantum efficiency is lowered. Therefore, a thin film is formed by determining the logarithm of the dielectric multilayer mirror 111 so as to obtain the above-described reflectance. In addition, it is an important requirement to use a dielectric material having a characteristic that the light absorption loss is small with respect to the laser oscillation wavelength in order to lower the threshold and improve the external differential quantum efficiency.

FIG. 16 shows a surface emitting semiconductor laser device in which an amorphous Si and SiO _x multilayer mirror is formed as a dielectric multilayer mirror indicated by a solid line 1602, and ZrTiO _x as a dielectric multilayer mirror indicated by a solid line 1601. And IL characteristics of the surface-emitting type semiconductor laser device in which a multilayer mirror of SiO _x is formed. More specifically, the solid line 1601 in the figure shows the IL characteristic of the surface emitting semiconductor laser device in which eight pairs of SiO _x / ZrTiO _x multilayer films are formed as dielectric mirrors and the reflectance is 99.0%. A solid line 1602 indicates the IL characteristic of a surface-emitting type semiconductor laser device in which four pairs of SiO _x / amorphous Si multilayer films are formed as dielectric mirrors and the reflectance thereof is 98.7%. As is apparent from FIG. 16, the external differential quantum efficiency and the oscillating light output are greatly different from those of the dielectric multilayer mirror having substantially the same reflectance. This is because amorphous Si has a light absorption coefficient of 4000 cm ⁻¹ for a wavelength of 800 nm, whereas ZrTiO _{x has} a small light absorption coefficient of 50 cm ⁻¹ for the same wavelength.

  Table 1 shows a refractive index and a light absorption coefficient with respect to a wavelength of 800 nm of a dielectric thin film formed by an electron beam evaporation method (hereinafter referred to as an EB evaporation method).

In Table 1, ZrTiO _x is a dielectric material in which Ti in ZrO _x is contained in a thin film at a molar ratio of about 5% with respect to Zr. In order to form the reflection mirror, the film thickness is λ / 4n (n is the refractive index of the dielectric material) with respect to the oscillation wavelength λ, and the low refractive index dielectric and the high refractive index dielectric are alternately used. Laminate. To increase the reflectivity, the reflectivity increases as the number of logs to be stacked is increased. However, the reflectivity cannot be increased if there is an absorption loss of light.

  Next, Table 2 shows the mirror film thickness and logarithm for each combination of dielectrics, the calculated value of the reflectance at λ = 800 nm, and the reflectance of each dielectric mirror fabricated by EB deposition.

The calculated values of the reflectance in Table 2 above are the results in consideration of the light absorption coefficient in Table 1. As can be seen from Table 2, it is difficult to increase the reflectivity when a dielectric material having a large absorption coefficient such as a-Si (amorphous silicon) is used. As described above, the dielectric multilayer mirror used in the surface-emitting type semiconductor laser device of the embodiment of the present invention has a light of 100 cm ⁻¹ or less with respect to the oscillation wavelength in order to reduce the threshold current value and increase the light emission efficiency. The mirror is preferably formed using a dielectric material having an absorption coefficient, more preferably a light absorption coefficient of 60 cm ⁻¹ or less.

  Next, further conditions necessary for realizing a surface emitting semiconductor laser device having a low oscillation threshold and high efficiency will be described.

FIG. 17A is a diagram schematically showing a cross-sectional structure of the surface-emitting type semiconductor laser device showing the embodiment of the present invention shown in FIG. In FIG. 17A, the same reference numerals as those in FIG. 1 denote the same components, 1701 indicates a resonator length, and 1702 schematically indicates the flow of injected current. The surface emitting semiconductor laser device can form a Fabry-Perot resonator between the dielectric multilayer mirror 111 and the DBR mirror 103 and oscillate at a wavelength of a standing wave standing in the resonator. . The resonator length 1701 is almost determined by the film thickness between the dielectric multilayer mirror 111 and the DBR mirror 103. Since there is light penetration into the DBR mirror 103, the effective resonator length (hereinafter referred to as this) “L _eff ”) is longer than the length indicated by 1701. This effective resonator length L _eff can be directly measured by examining the reflectance.

  FIG. 17B shows a stripe formed using a wafer having a semiconductor layer (hereinafter also simply referred to as “semiconductor laminated wafer”) for forming the surface emitting semiconductor laser device of this embodiment shown in FIGS. 1 and 17A. 1 shows an example of an edge-emitting semiconductor laser device of a mold. That is, as shown in FIG. 22A, the edge-emitting semiconductor laser device 200 includes a DBR mirror 103, a first cladding layer 104, a quantum well active layer 105, a second cladding layer 106, and a contact layer 109 on a substrate 102. This is obtained by cutting out a part of the semiconductor laminated wafer on which is laminated, forming the insulating layer 120 and the upper electrode 121 on the contact layer 109, and forming the lower electrode 101 below the substrate 102. This edge-emitting semiconductor laser device serves as a sample for obtaining a peak wavelength of gain described later. As the edge emitting semiconductor laser device, a stripe-buried edge emitting laser, a mesa stripe edge emitting laser, or the like can be used.

  FIG. 18 shows the reflectance spectrum (curve 1801) of the DBR mirror, the reflectance spectrum (curve 1802) of the wafer (semiconductor laminated wafer), and the oscillation spectrum (curve 1803) of the edge-emitting semiconductor laser device 200. The results are shown. In FIG. 18, the vertical axis for the curves 1801 and 1802 indicates the reflectance, the vertical axis for the curve 1803 indicates the emission intensity, and the horizontal axis indicates the wavelength.

  In the curve 1801, the region where the reflectance is 99.2% or more has wavelengths from 792 nm to 833 nm. In the case of this semiconductor laminated wafer, the oscillation wavelength of the surface emitting semiconductor laser device is designed to be 800 nm.

  In order to achieve low threshold and high efficiency of the surface emitting semiconductor laser device, these three spectra need to satisfy specific conditions.

[First condition]
First, the first condition requires that the DBR mirror reflectivity is sufficiently high with respect to the oscillation wavelength. The reflectance peak of the DBR mirror is obtained by accurately controlling the film thickness of the semiconductor layer (Al _0.8 Ga _0.2 As / Al _0.15 Ga _0.85 As) constituting the DBR mirror. The reflectance value can be increased by increasing the logarithm of the DBR mirror. By the way, since the film thickness of the crystal layer is usually not completely uniform within the wafer surface, the reflectance spectrum of the DBR mirror has a distribution on the short wavelength side and the long wavelength side within the wafer surface. Therefore, the reflectivity of the Al _0.8 Ga _0.2 AS / Al _0.15 Ga _0.85 AS DBR mirror has a reflectivity of at least 99.2% in the range of ± 20 nm with respect to the oscillation wavelength. Otherwise, there will be a region in the wafer surface where no laser oscillation occurs. In this embodiment, 40 pairs of semiconductor layers are stacked as DBR mirrors. Therefore, as is apparent from the curve 1801 in FIG. 18, even if there is a thickness distribution of ± 2.5% in the wafer surface, for example. It is possible to cause laser oscillation at a target oscillation wavelength.

The reflectivity of the DBR mirror also varies depending on the doping amount of each layer of the semiconductor layer (Al _0.8 Ga _0.2 AS / Al _0.15 Ga _0.85 AS) constituting the mirror. This is because when the doping amount of each layer increases, the light absorption loss due to the generated free carriers cannot be ignored.

In particular, in the Al _0.8 Ga _0.2 AS / Al _0.15 Ga _0.85 AS DBR mirror in this example, when the doping amount of Se, which is an n-type dopant, exceeds 1 × 10 ¹⁹ cm ^−3. Even if the number of pairs is 40, it becomes difficult to obtain a reflectance of 99.2% or more at the set wavelength ± 20 nm. Therefore, the doping amount of each layer is preferably 1 × 10 ¹⁹ cm ⁻³ or less. Table 3 shows the relationship between the average doping amount of the DBR mirror and the reflectance.

However, lowering the doping amount of the DBR mirror increases the electric resistance of the DBR mirror, and increases the element resistance in a surface-emitting laser in which current flows in the DBR mirror. Since the surface emitting laser of this embodiment has a structure in which the DBR mirror is not etched in a columnar shape, the drive current spreads over the entire DBR mirror, and the increase in the resistance of the DBR mirror has little influence on the increase in resistance of the laser element. However, when the doping amount in each layer of the DBR mirror is less than 5 × 10 ¹⁶ cm ⁻³ , the resistance of the DBR mirror becomes almost the same as the contact resistance of the upper contact layer and the electrode even in the structure of this example. Therefore, the influence on the element resistance cannot be ignored. Therefore, there is a suitable range for the doping amount to each layer constituting the DBR mirror, and the range is 5 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ¹⁹ cm ⁻³ or less. Further, in view of the degree of freedom of the oscillation wavelength, such as the production of a surface emitting laser having a different oscillation wavelength from one substrate, it is more preferably 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less. desirable.

Furthermore, the DBR mirror in this embodiment desirably has the following configuration with respect to the doping amount. That is, a first layer (a layer having a high aluminum concentration) constituting a DBR mirror and a second layer (a layer having a low aluminum concentration) having a smaller band gap and a different refractive index than the first layer. It is desirable to make the carrier concentration in the vicinity of the interface higher than the region other than the vicinity of the interface. Here, “carrier concentration” refers to the carrier concentration of electrons or holes generated by impurity doping. The carrier concentration can be changed by changing the doping amount. Specifically, the maximum value of the carrier concentration in the vicinity of the interface is preferably 1.1 times or more and 100 times or less the minimum value of the carrier concentration in the vicinity of the interface. Further, the maximum value of the carrier concentration in the vicinity of the interface preferably takes a value of 5 × 10 ²⁰ cm ⁻³ or less.

  Thus, by forming a portion with a high carrier concentration at the heterointerface between the first layer and the second layer constituting the DBR mirror, it is possible to enhance the tunnel conduction of electrons and holes, and thus to prevent The continuous bunt structure is improved, and a low resistance DBR mirror can be constructed. Further, since the refractive index distribution of the mirror is not greatly affected by increasing the carrier concentration at such a hetero interface, the reflectance of the mirror does not decrease.

  Next, in manufacturing such a DBR mirror, a method of changing the dopant raw material with time, a method of irradiating the growth surface with ultraviolet rays at a predetermined timing, and a ratio of the group V raw material and the group III raw material with time are set. By adopting a method of changing the carrier concentration, the carrier concentration can be increased only in the vicinity of a predetermined interface.

  Hereinafter, such DBR mirrors will be described in more detail with experimental data.

First, the growth process of the DBR mirror will be described. FIG. 35 is a timing chart showing changes in the flow rates of TMGa and TMAl, which are the raw materials of the DBR mirror, and changes in the flow rate of H ₂ Se, which is the raw material of the n-type dopant. In this example, since TMGa is constantly supplied, the growth portion with a high TMAl flow rate is an n-type Al _0.8 Ga _0.2 As layer, and the growth portion with a low TMAl flow rate is an n-type Al _0.15. A Ga _0.85 As layer will be formed. Here, the thickness of each layer is controlled to be ¼ wavelength of light having a wavelength of 800 nm propagating in the layer. Further, a portion with a high H ₂ Se flow rate as a dopant indicates a growth portion where n-type carriers are to be doped at a high concentration, and a portion with a low H ₂ Se flow rate indicates a growth portion where the n-type carriers are to be doped at a low concentration. ing. In the MOVPE apparatus, the change in the flow rate is controlled by switching the computer-controlled valve between a line with a high H ₂ Se flow rate and a line with a low H ₂ Se flow rate. In this example, the portion where the dopant Se amount is high is the growth portion where the TMAl flow rate is high, that is, the n-type Al _0.15 Ga _0.85 As layer in the n-type Al _0.8 Ga _0.2 As layer. The concentration of Se formed in the vicinity of the interface is controlled so as to decrease sharply at the interface with the growth portion where the TMAl flow rate is low, that is, the n-type Al _0.15 Ga _0.85 As layer.

  FIG. 36 shows the result of evaluating a part of the DBR mirror thus obtained by the SIMS (secondary ion mass spectrometry) method. In FIG. 36, the vertical axis indicates the number of secondary ions of Al and Se, and corresponds to the amount of atoms and the number of carriers contained in the layer. The horizontal axis indicates the depth in the film thickness direction in a part of the DBR mirror.

When FIG. 35 and FIG. 36 are compared, the concentration of Se, which is an n-type dopant, is the second layer (n-type Al _0.8 .0) in the first layer (n-type Al _0.8 Ga _0.2 As layer) _{. 15} Ga _0.85 As layer) in the vicinity of the interface, and it was confirmed that doping was performed as prescribed.

Next, the effect | action of a present Example is demonstrated using the schematic diagram of the energy band of a DBR mirror shown in FIG. FIG. 37A shows a case where the concentration of Se is sharply increased in the vicinity of the interface between the first layer and the second layer in this embodiment, and FIG. 37B supplies the H ₂ Se flow rate at a constant low concentration. The case where it created similarly to a present Example except having performed was shown. Comparing the two, in this example, as the carrier concentration near the interface increases, the conduction band barrier becomes thinner, and as a result, the electrons are more likely to tunnel, thereby reducing the electrical resistance in the direction perpendicular to the multilayer film. To be understood. Here, since the carrier concentration is increased by doping only in the vicinity of the interface of the layers, there is no substantial deterioration of the film quality due to the high concentration doping.

  As a method of increasing the carrier concentration in the vicinity of the interface, a method of irradiating light such as ultraviolet rays can be used in addition to the method of controlling the doping amount described above.

Specifically, ultraviolet light is irradiated during the growth of a portion where the carrier concentration is to be increased. FIG. 38 is a timing chart of TMAl flow rate change and light irradiation during the growth of the DBR mirror. The growth part with a high TMAl flow rate is the first layer (n-type Al _0.8 Ga _0.2 As layer), and the growth part with a low TMAl flow rate is the second layer (n-type Al _0.15 Ga _0.85 As). Layer). Here, the thickness of each layer is controlled to be ¼ wavelength of light having a wavelength of 800 nm propagating in the layer. In this embodiment, the irradiation with ultraviolet light is performed in the growth portion where the TMAl flow rate is high, that is, in the vicinity of the interface with the second layer in the first layer. As the n-type dopant, tetramethylsilane (TMSi) is used instead of H ₂ Se.

  FIG. 39 shows the result of evaluating a part of the DBR mirror thus obtained by the SIMS method. In FIG. 39, the vertical axis indicates the number of secondary ions of Al and Si, and corresponds to the amount of atoms and the number of carriers contained in the film. The horizontal axis indicates the depth in the film thickness direction in a part of the DBR mirror.

  Comparing FIG. 38 with FIG. 39, it can be seen that in the layer irradiated with ultraviolet light, the concentration of Si, which is an n-type dopant, rapidly increases, and the layer has a high carrier concentration. This is due to the following reason. That is, TMSi which is a doping material is extremely stable thermally and hardly thermally decomposed, but has an absorption band in the ultraviolet region, so that it is easily photodecomposed by irradiation with ultraviolet light. Therefore, when the ultraviolet light is irradiated, the Si concentration in the growth layer is rapidly increased and the supply amount of the n-type doping substance is substantially increased as compared with the case where the ultraviolet light is not irradiated. As in the case of the Se dopant described above, the carrier concentration in the vicinity of the interface of the layers constituting the DBR mirror is increased. As a result, the conduction band barrier is thinned and electrons are easily tunneled, and therefore perpendicular to the multilayer film. The electrical resistance in any direction will be reduced. Further, here, the carrier concentration is increased by doping only in the vicinity of the interface of the layers, and further, since light irradiation contributes to the improvement of the film quality, there is no substantial deterioration of the film quality due to the high concentration doping.

  In the interface doping described above, S, Se, Te, Zn, C, Be, Mg, Ca, etc. can be used as the dopant material in addition to Se and Si. When a GaAs-based material with low doping efficiency such as Te or Mg is used, the flow rate of AsH3, which is a V group material, is controlled at a location where high concentration doping is desired, and the ratio (V / By changing III), the doping efficiency can be controlled.

  Furthermore, the method for controlling the carrier concentration at the heterointerface is not limited to increasing the carrier concentration in the vicinity of the interface in the layer having a large band gap as described above, and the carrier concentration in the vicinity of the interface is increased in the layer having a small band gap. Further, the carrier concentration in the vicinity of the interface in both the layer having a large band gap and the layer having a small band gap may be increased. Furthermore, the relationship between the carrier concentration distribution and the multilayer film reflectivity, the multilayer vertical film electrical resistance, and the multilayer film crystallinity was examined in detail. Is preferably within 1/3 of the combined thickness of the first layer having a large band gap and the second layer having a small hand gap. It was confirmed that when the region having a high carrier concentration was made thicker than this, the crystallinity deteriorated. In order to reduce the resistance of the DBR mirror, it is desirable to instantaneously switch the timing of the high concentration doping and the low concentration doping, but it is confirmed that the crystallinity is slightly deteriorated by this operation depending on the doping material. It was. In this case, the supply amount of the raw material is continuously changed from the supply amount of the raw material when doping other than the vicinity of the interface to the supply amount of the raw material when doping near the interface, instead of switching the doping amount sharply. It is desirable. That is, before doping in the vicinity of the interface with a predetermined doping concentration, the doping amount is linearly, quadratic or cubically functioned by taking a time within half of the doping time in the vicinity of the interface. By changing it, it is possible to suppress a decrease in crystallinity.

[Second condition]
Next, the second condition is that the wavelength of the standing wave in the above-described resonator length becomes the oscillation wavelength of the surface-emitting type semiconductor laser device. Therefore, the effective resonator length is the oscillation wavelength in the resonator. (This is called “mode resonance condition”). It can be seen from the curve 1802 shown in FIG. 18 that a clear dip is observed in the spectrum at the wavelength of _λEM shown in the figure. This dip is a semiconductor layer formed on the DBR mirror, and a standing wave is generated at the wavelength _λEM , and light of that wavelength is resonantly absorbed in the resonator. Therefore, if the reflectance spectrum of the semiconductor laminated wafer for the surface emitting semiconductor laser device is measured, the above-described effective resonator length L _eff can be directly measured. The above-described mode resonance condition means that the wavelength _λEM is included in the high reflectance band (peak) of the reflectance spectrum of the DBR mirror indicated by the curve 1801.

[Third condition]
The third condition, the peak wavelength of the gain of the active layer, is that there needs to be located on the shorter wavelength side with respect to the wavelength lambda _EM of a standing wave in the mode resonance condition described above. A curve 1803 in FIG. 18 is obtained by measuring a laser oscillation spectrum of an edge-emitting semiconductor laser device 200 (see FIG. 17B) manufactured using the same semiconductor laminated wafer from which the spectrum 1802 was obtained. It is. Here, in the surface emitting semiconductor laser device and the edge emitting semiconductor laser device 200 from which the curve 1802 is obtained, the n-type cladding layer, the active layer, and the p-type cladding layer are formed of the same semiconductor layer. In addition to the gain spectrum of the active layer of the edge-emitting semiconductor laser device, the gain spectrum of the active layer of the surface-emitting semiconductor laser is also expressed. The peak wavelength of the gain spectrum is denoted as λ _G in the figure. the difference between the wavelength of λ _EM and λ _G is referred to as △ λ _BS. The third condition of this embodiment, lambda _G is located always on the short wavelength side of lambda _EM, and the difference △ lambda _BS is that is within 20 nm.

  This third condition is an important feature that the applicant of the present application reveals for the first time. Hereinafter, why the third condition is an indispensable condition for the surface-emitting type semiconductor laser device of the present invention will be described in detail.

  FIG. 19A is a diagram showing the relationship between the oscillation wavelength of the edge-emitting semiconductor laser device 200 and the case temperature. FIG. 19B is a measurement result based on FIG. 19A and shows an oscillation spectrum at each case temperature. Here, the case temperature is the temperature of the package on which the laser device is mounted, and it may be considered that the case temperature and the temperature of the laser device are substantially the same.

  As is apparent from FIG. 19A, the oscillation wavelength shifts to the long wavelength side almost linearly with increasing temperature. The rate of change Δλ / ΔT is 2.78 Å / ° C. This is because the peak wavelength of the gain spectrum shifts to the longer wavelength side due to temperature rise.

  On the other hand, FIG. 20A shows the relationship between the oscillation wavelength and the case temperature in the case of a surface emitting semiconductor laser device. Similar to the edge-emitting semiconductor laser device, the oscillation wavelength shifts to the long wavelength side almost linearly with increasing temperature. As described above, since the oscillation wavelength of the surface-emitting type semiconductor laser device is determined by the effective resonator length, the oscillation wavelength becomes longer due to the change in the refractive index of the semiconductor constituting the resonator due to the temperature rise. This is due to the shift to the wavelength side. However, the rate of change Δλ / ΔT is 0.41 angstrom / ° C., which is as small as about 1/7 compared with the edge-emitting semiconductor laser device. Therefore, in the case of a surface emitting semiconductor laser device, the peak wavelength of the gain spectrum moves to a longer wavelength side than the change of the oscillation wavelength due to the change of the refractive index due to the temperature rise.

FIG. 20B shows how the junction temperature (junction temperature) and the oscillation wavelength of the surface-emitting type semiconductor laser device are increased by direct current injection. As apparent from FIG. 20B, the junction temperature increases in proportion to the square of the injection current density, and the gain spectrum peak and the oscillation wavelength are increased by current injection in the same manner as the case temperature increase described above. It will shift to the wavelength side. Also in this case, the peak of the gain spectrum is larger than the oscillation wavelength and shifted to the longer wavelength side. Therefore, in order to cause laser oscillation by current injection and to obtain high efficiency by reducing the threshold current, the peak of the gain spectrum is set in advance on the shorter wavelength side than the laser oscillation wavelength determined by the effective resonator length. There is a need. This preset wavelength difference (Δλ _BS ) is hereinafter referred to as “gain offset amount”. This is because if the peak of the gain spectrum is on the longer wavelength side than the oscillation wavelength, the gain spectrum peak is shifted to the longer wavelength side due to current injection, and the gain necessary for laser oscillation is reduced. However, if the gain spectrum peak is set too large on the short wavelength side, even if the gain spectrum peak is shifted to the long wavelength side due to current injection, the gain at the oscillation wavelength becomes too small to cause lasing from the beginning. End up.

According to the applicant's experiment, when the gain offset amount Δλ _BS is larger than 20 nm, laser oscillation does not occur, and when the gain offset amount Δλ _BS is smaller than 5 nm, the optical output is saturated immediately, and therefore Δλ _BS is between 5 nm and 20 nm. It is desirable to be.

The basis for the numerical range of the gain offset amount Δλ _BS will be described with reference to FIG. In Figure 21, the vertical axis represents the threshold current _{I th,} the horizontal axis shows the gain offset △ lambda _BS. In this embodiment, for example, when the diameter Da of the resonator portion is 8 μm, the threshold current for setting the current density to, for example, 10 kA / cm ² at the maximum level is 5 mA. Considering this threshold current, the limit gain offset Δλ _BS at which the surface emitting semiconductor laser device continuously drives is about 20 nm from FIG. On the other hand, from FIG. 21, when the gain offset amount Δλ _BS is smaller than about 5 nm, the threshold current increases and the light output is saturated immediately. From this, the gain offset amount Δλ _BS is preferably 5 to 20 nm, more preferably 5 to 15 nm, and most preferably 10 to 15 nm. FIG. 21 shows data obtained by specifying the values of the diameter Da of the resonator portion and the diameter Dw of the opening. Even if Da and Dw are different, the oscillation threshold value is within the range of Da and Dw of this embodiment. Since the current densities are substantially the same, the third condition is satisfied with little dependence on Da and Dw.

Further, when the temperature of the surface emitting semiconductor laser device changes, the peak wavelength of the gain spectrum of the surface emitting semiconductor laser also changes as described above. Therefore, the measurement of the aforementioned lambda _G is measured in the vicinity of temperatures using a surface-emitting type semiconductor laser device.

  Although the conditions regarding the spectrum have been described above, further, as a characteristic necessary for the surface emitting semiconductor laser device, it is required that laser oscillation occurs in the fundamental transverse mode and that it does not change even when the injection current is increased. When laser oscillation is performed in a high-order transverse mode, the radiation beam has a complex structure without becoming unimodal, and when this is optically condensed or imaged, it becomes a distributed image and is practically used. No. 24A and 24B show the results of measurement relating to the transverse mode characteristics of the oscillation light of the surface emitting semiconductor laser device having the structure of the present invention. FIG. 24A shows the measurement results obtained by displaying the far-field image of the oscillation light of the surface emitting semiconductor laser device with Da = 8 μm and Dw = 6 μm as contour lines. In this case, the contour lines indicate the distribution depending on the radiation angle from the surface emitting semiconductor laser device. FIG. 24B shows a far-field image obtained in the case of a surface emitting semiconductor laser device with Da = 13 μm and Dw = 10 μm obtained by the same measurement. In the far-field image shown in FIG. 24A, the laser beam has a perfect circular laser beam shape with a half-value radiation angle of 8 degrees, indicating that it oscillates in the fundamental transverse mode. On the other hand, the far-field image shown in FIG. 24B has a bimodal shape, indicating that it oscillates in a high-order transverse mode.

  Therefore, as is clear from FIGS. 24A and 24B, the transverse mode characteristics of the laser differ greatly depending on the size of the resonator diameter (Da) and the opening diameter (Dw). As described above, the radiated light needs to be in the fundamental transverse mode. For this purpose, it is not preferable to make the diameter of the resonator portion larger than a certain size. Further, the output of the oscillating light is advantageous in obtaining a high light output because the light intensity density on the emission surface becomes smaller as the size of the resonator is larger. Therefore, it is not preferable to make the size of the resonator too small. Table 4 shows the relationship between the magnitudes of Da and Dw, the transverse mode, and the light output capable of oscillation.

  As apparent from Table 4, when the diameter Da of the resonator 114 exceeds 12 μm and the diameter Dw of the opening 113 exceeds 10 μm, the transverse mode becomes higher order, and the emitted light does not have a single peak but a plurality of peaks. It has a certain structure. Further, when Da is 6 μm or less and Dw is 4 μm or less, the maximum light output can be obtained only about 0.5 mW. Further, when Da is 12 μm and Dw is 8 μm, when the injection current is increased, the transverse mode shifts to a higher-order mode at a relatively low current value, and an unstable region of light output is formed (hereinafter referred to as “light output”). , This is described as "kink generation"). Therefore, in the embodiment of the present invention, the basic transverse mode oscillation condition is that Da is 6 μm to 12 μm and Dw is 4 μm to 8 μm, and more preferably, Da is 7 μm to 10 μm. , Dw is 5 μm to 7 μm.

  Next, how the film thickness of the portion of the second cladding layer 106 in FIG. 1 forming the resonator affects the lower threshold of the laser device will be described based on an experimental example. As shown in FIG. 17, in the structure of the surface emitting semiconductor laser device of the present invention, current is injected from the ring-shaped upper electrode 112 into the active layer 105. Laser oscillation occurs near the center of the resonator where the largest gain is obtained. This is because the light traveling back and forth in the resonator has a large optical loss at the interface between the upper electrode and the resonator in the periphery of the resonator, and thus obtains a maximum gain near the center. However, since the injection current flows from the upper electrode to the active layer through the second cladding layer, a non-uniform current density distribution is generated inside the resonator. Therefore, in order to obtain a carrier density by an injection current sufficient for laser oscillation at the center of the resonator, the film thickness of the second cladding layer needs to be selected appropriately. If the injected carrier density is insufficient, the threshold current increases.

  FIG. 25A shows an emission near-field image when the thickness of the second cladding layer 106 is 1.0 μm in the laser device of this example, and FIG. 25B shows an emission near-field when the thickness of the second cladding layer 106 is 0.3 μm. A field image is measured. Each figure in the lower stage shows the light intensity at lines aa and bb in the figure. FIG. 25A is a near-field image of laser emission. FIG. 25B shows a near-field image of spontaneous emission that does not lead to laser oscillation. As is clear from FIG. 25B, when the film thickness of the second cladding layer is thin, the nonuniformity of the injected carriers is large, and many of the injected carriers are distributed at positions corresponding to the upper electrode 112 (contact metal). Recombine and emit light, and the injected carrier density near the center of the resonator does not increase. Therefore, the light output is thermally saturated before the laser oscillation threshold is reached. On the other hand, when the second cladding layer 106 has a sufficient film thickness as shown in FIG. 25A, a uniform injected carrier density can be obtained inside the resonator, so that the maximum gain can be obtained near the center of the resonator. Has led to laser oscillation.

  Therefore, in the case of the structure of the surface emitting semiconductor laser device of the present invention, if the thickness is too thin, the cladding layer causes nonuniformity of injected carriers, resulting in an increase in the laser oscillation threshold current, In some cases, laser oscillation itself may not be achieved. FIG. 26 shows measurement results of IL characteristics when the thickness of the second cladding layer 106 is 0.3 μm and 2.0 μm. Curve (a) shows a case where the film thickness is 0.3 μm. In this case, even if the injection current is increased, laser oscillation does not occur, and the light output is saturated only by spontaneous emission light. On the other hand, when the film thickness shown by the curve (b) is 2.0 μm, laser oscillation is started with a threshold current value of 3 mA, and oscillation is possible up to a maximum optical output of 1.5 mW with a slope efficiency of 0.35 W / A. is there.

  However, if the thickness of the second cladding layer becomes too thick, the device resistance of the device increases, leading to an increase in power consumption, and the problem that the thermal saturation of the optical output occurs with a low injected current, or the entire device As the film thickness increases, it takes a long time for crystal growth, resulting in a problem that the manufacturing efficiency of the wafer is lowered. In this embodiment, when the film thickness of the second cladding layer is 3.5 μm or more, the element resistance exceeds 100Ω, and the maximum value of the light output decreases. FIG. 27 shows IL characteristics when the thickness of the second cladding layer is 2.0 μm and when the film thickness is 4.0 μm. Curve (a) is when the film thickness is 2.0 μm, and curve (b) is when the film thickness is 4.0 μm. As apparent from FIG. 27, when the thickness of the second cladding layer becomes too thick, the resistance of the second cladding layer increases, and when the injection current is increased, the current with low thermal saturation of the optical output due to the temperature rise of the device. To happen by value.

  As described above, the thickness of the second cladding layer has an optimum thickness, and in the present invention, it is preferably 0.8 μm to 3.5 μm, and more preferably 1.0 μm to 2.5 μm.

Further, in order to make the injected carriers uniform in the second cladding layer and obtain a uniform injected carrier density in the active layer, it is also effective to reduce the specific resistance of the second cladding layer. Even when the thickness of the cladding layer is small, the same effect as that of increasing the thickness of the second cladding layer can be obtained by lowering the specific resistance and improving the diffusion of injected carriers. Table 5 shows the diffusion length of the injected carrier with the specific resistance when the thickness of the Al _0.7 Ga _0.3 As layer constituting the second cladding layer is 1 μm.

When the diameter Dw of the surface emitting laser opening is about 8 μm, the diffusion length of the injected carriers is good, and considering this relationship, from Table 5, the specific resistance is 2 × 10 ⁻¹ Ω · cm or less. It turns out that it is preferable to do. However, as in the case of the doping amount in the DBR mirror, if the specific amount of the second cladding layer is increased to less than 7 × 10 ⁻³ Ω · cm by the doping amount, the free clad generated by doping is caused. Light absorption cannot be ignored, resulting in a decrease in light emission efficiency. Therefore, the specific resistance of the second cladding layer is preferably 7 × 10 ⁻³ Ω · cm to ¹ × 10 ⁻¹ Ω · cm.

  More preferably, both the preferred thickness range of the second cladding layer and the preferred specific resistance range of the second cladding layer are satisfied.

Next, a manufacturing method for realizing a surface emitting semiconductor laser device having a low threshold current as described above and high external differential quantum efficiency will be described in detail. As described above, since the DBR mirror layer and the multiple quantum well structure are formed by crystal growth, the crystal growth technique is one of the most important elements in the surface emitting semiconductor laser device of the present invention. Crystal growth technology includes
(1) The heterointerface is steep in the atomic layer order. (2) The film thickness is highly uniform over a wide area. (3) The film thickness, composition, and reproducibility of doping efficiency are high. is there. In particular, the sharpness of the interface (1) is important for improving the characteristics of the surface emitting semiconductor laser device. Methods for ensuring the sharpness of the interface in the compound semiconductor crystal growth technique include a molecular beam epitaxy method (MBE method) and a metal organic vapor phase epitaxy method (MOVPE method). The liquid phase epitaxy method (LPE method) allows high-purity crystal growth, but since it is a growth method from the liquid phase to the solid phase, it is difficult to realize the steepness of the heterointerface, and the surface emitting semiconductor laser It is not suitable for the manufacturing method of the device. On the other hand, the MBE method and the MOVPE method are growth methods from a molecular beam and a gas phase to a solid phase, respectively.

  However, the MBE method is a crystal formation from a molecular beam, and the growth rate cannot be increased, and only a relatively slow growth rate of 0.1 to 1 angstrom / second can be obtained, which is about several μm like a surface emitting laser. It is not suitable for crystal growth that requires an epitaxial layer. Further, in the MBE method, it is very difficult to grow crystals uniformly and with high quality in a large area due to the structure of the manufacturing apparatus, and the number of continuous crystal growths is limited due to the restriction of the amount of raw material filling. This is a point that limits the throughput of crystal growth and is a factor that makes it difficult to mass-produce substrates.

  On the other hand, the MOVPE method used in this example is a heterostructure having an atomic layer order equivalent to that of the MBE method as shown in the relationship between the film thickness of the quantum well structure and the peak wavelength (see FIG. 10). A steepness of the interface is obtained, and since it is vapor phase growth, a growth rate of 0.1 to several tens of angstroms / second can be obtained by changing the supply amount of the raw material.

  Further, regarding the uniformity of the film thickness of (2), by optimizing the shape of the reaction tube of the growth apparatus, for example, as shown in FIG. It was confirmed that a film thickness distribution of 2% was obtained.

  In terms of the reproducibility of (3), the MBE method and the MOVPE method have good controllability of growth in principle, so the reproducibility of the film thickness, composition and doping efficiency is high.

  Therefore, the MOVPE method is preferable as the crystal growth method for realizing the surface emitting semiconductor laser device of the present invention.

  With respect to the point (3), an epitaxial layer can be formed with higher reproducibility and controllability by combining the following manufacturing methods with the MOVPE method.

  FIG. 29 shows an example of a film forming apparatus to which the MOVPE method is applied and which can always measure the reflectance of the epitaxial layer during crystal growth. This film forming apparatus is a MOVPE apparatus using a horizontal water-cooled reaction tube, and has a structure having a window that allows light to enter the growth substrate from the outside of the reaction tube by eliminating the water-cooled tube portion above the growth substrate. .

  That is, this MOVPE apparatus is provided with a cooling unit 12 that cools the reaction tube by passing water through the inside of the reaction tube 10 having the gas supply unit 10a to which the source gas is supplied and the gas discharge unit 10b. Yes. A susceptor 14 for placing the substrate S is provided inside the reaction tube 10, and a window 16 is provided on the wall of the reaction tube 10 facing the substrate placement surface of the susceptor 14. A light source 18 and a photodetector 20 are installed above the window 16, and light emitted from the light source 18 reaches the substrate S on the susceptor 14 through the window 16, and the reflected light again passes through the window 16. It is configured to reach the photodetector 20.

  Then, the light from the light source 18 is set to be incident substantially perpendicularly (up to 5 °) on the substrate S, and the reflected light is measured by the photodetector 20, thereby performing epitaxial growth on the substrate S. It is possible to measure the change in the reflectance of the epitaxial layer that is generated simultaneously.

  In this embodiment, in order to set the central wavelength of the DBR mirror as the oscillation wavelength, a semiconductor laser having an oscillation wavelength of 800 nm which is the same as the central wavelength of 800 nm is used as the light source 18. It should be noted that the reflectance of an arbitrary wavelength can be measured by using a wavelength tunable light source using a semiconductor laser or a spectroscope having a wavelength different from that of 800 nm as the light source 18.

  From the above-described relationship between the reflectance of the DBR mirror and the emission characteristics of the surface emitting semiconductor laser device (see FIG. 18), the DBR mirror is desired to have a reflectance of 99.5% or more at a predetermined wavelength. Yes. In order to satisfy this, the thickness of each layer constituting the DBR mirror must be λ / 4n. Here, λ is a predetermined wavelength, and n is a refractive index at a predetermined wavelength.

  In the conventional crystal growth method, the film thickness of each layer is controlled by the crystal growth rate and the growth time. However, this method has several problems. The first problem is that the crystal growth rate must always be constant in this method, and if the growth rate fluctuates, it is difficult to obtain a reflectance of 99.5% or higher even if the number of DBR mirror pairs is increased. It is. The second problem is that the refractive index n is a factor that determines the film thickness. However, since the refractive index of the semiconductor layer also changes depending on the wavelength, the refractive index of each layer at a predetermined wavelength is also strictly measured. And this measurement is very difficult. Further, the third problem is that the reflectance is measured by taking out the wafer after crystal growth from the reaction tube and measuring only the reflectance including the structure above the DBR mirror. Cannot be measured.

  These problems can be solved by performing epitaxial growth by the MOVPE method while measuring the reflectance. The mechanism will be described below.

  FIG. 30 shows the change over time in the reflectance of the epitaxial layer during the MOVPE growth of the DBR mirror 103 constituting the surface emitting semiconductor laser device of this example using the film forming apparatus shown in FIG. It is.

As is apparent from FIG. 30, when Al _0.8 Ga _0.2 As having a low refractive index n1 is first laminated on a GaAs substrate, the reflectance decreases as the film thickness increases. When the film thickness becomes (λ / 4n ₁ ), the minimum point (1) is directed, so this minimum point is monitored and switched to deposition of Al _0.15 Ga _0.85 As with a high refractive index n ₂ . Then, the reflectance increases as the film thickness of the Al _0.15 Ga _0.85 As layer increases. However, when the film thickness reaches (λ / 4n ₂ ), the maximum point (2) is reached, so that the reflectance decreases again. Switch to the product of Al _0.8 Ga _0.2 As with refractive index n1. By repeating this operation, the reflectivity of the DBR mirror fluctuates while repeating low reflectivity and high reflectivity, and the reflectivity increases.

  This reflectance profile does not depend on the growth rate or growth time of the crystal but depends on the film thickness and refractive index of each layer. Therefore, by changing the Al composition of the layers to be stacked at the maximum and minimum points (first derivative value 0) of the reflectance profile, and by alternately epitaxially growing layers having different refractive indices, each layer has a theoretical thickness ( A DBR mirror with λ / 4n) is obtained. Further, by selecting a semiconductor laser having a predetermined oscillation wavelength as a light source of input light for measuring the reflectance, λ can be set strictly, so that the refractive index n can also be obtained from the film thickness of each layer.

  Furthermore, since the reflectance of the DBR mirror itself can be measured during crystal growth, the number of pairs of DBR mirrors can be changed during the layer formation, and the structure can be optimized.

  In addition, since the film thickness of each layer above the DBR mirror can be controlled based on the growth rate of each layer of the DBR mirror obtained from the reflectance measurement performed during the deposition of the DBR mirror, the crystal growth rate cannot be measured conventionally. The crystal growth substrate can be manufactured by a method with good reproducibility and high throughput as compared with the film forming method. Actually, the DBR mirror having a reflectivity of 99.5% or more necessary for the surface emitting laser element was obtained with good controllability by the growth method of this example.

  The above-described method for controlling the film thickness of the crystal layer by monitoring the reflectance of the layer can be used not only for the MOVPE method but also for other film forming processes such as the MBE method.

  Next, an embodiment in which the above-described means for monitoring the reflectance is used in the step of forming the columnar resonator portion by the RIBE method will be described.

  As described above, the resonator portion 114 is manufactured by etching using the RIBE method because a vertical side surface is obtained and surface damage is small. An important point in the formation of the columnar resonator portion is to control the etching depth, that is, the remaining film thickness t of the second cladding layer 106. The reason why the remaining film thickness must be controlled to a predetermined thickness is described above.

  A method of measuring the remaining film thickness while performing dry etching by the RIBE method will be specifically described below.

  FIG. 31 shows a schematic diagram of an example of a RIBE apparatus that can measure the reflectance of an epitaxial layer without etching.

  In this RIBE apparatus, a plasma chamber 40 and a vacuum pump 32 constituting exhaust means are connected to an etching chamber 30. The etching chamber 30 has a holder 34 for placing the substrate S at a position facing the plasma chamber 40. The holder 34 is provided so as to freely advance and retract through the load lock chamber 50. On the side wall of the etching chamber 30 on the plasma chamber 40 side, windows 36 and 38 are provided at positions facing each other. In the etching chamber 30, a pair of reflecting mirrors M1 and M2 are provided on a line connecting the windows 36 and 38. A light source 26 having an arbitrary wavelength is installed outside one window 36, and a photodetector 28 is installed outside the other window 38. The plasma chamber 40 is connected to a microwave introduction unit 44 and gas supply units 46 and 48 for supplying the reaction gas to the plasma chamber 40. A magnet 42 is provided around the plasma chamber 40. As the light source 26, light having an arbitrary wavelength, such as light passing through a spectroscope, can be used.

  In this RIBE apparatus, the crystal layer formed on the substrate S is etched by a normal method, and the light irradiated from the light source 26 is irradiated onto the substrate S through the window 36 and the reflection mirror M1, and the reflection thereof. By measuring the light with the photodetector 28 through the reflection mirror M1 and the window 38, the reflectance or reflection spectrum of the crystal layer on the substrate S can be monitored.

  Next, a method for measuring the remaining film thickness t of the second cladding layer during etching will be specifically described with reference to FIGS.

  The epitaxial crystal layer constituting the resonator in the pre-etching state (the state shown in FIG. 22A) shows a reflection spectrum as shown in FIG. 32A. This spectrum is similar to the spectrum 1802 shown in FIG. A characteristic of this spectrum is that the reflectance decreases at a certain wavelength λo, that is, there is a dip (Do).

  Since the wavelength λo of the dip (Do) corresponds to the film thickness of the crystal layer above the DBR mirror, when the film thickness is reduced by etching, the dip (Do) also moves to the short wavelength side and becomes the wavelength λ ′. (See FIG. 32B).

  Further, the next dip (D1) (wavelength: λ ″) is generated on the long wavelength side, and this shifts to the wavelength λ1 on the short wavelength side (see FIG. 32C). A new dip is generated, and the movement and generation of the dip are repeated.If the wavelength of the a-th dip is λa from the state before the etching, the etching amount Δa at this time is expressed by the following equation (3). expressed.

  In equation (3), Θ is a constant determined from the structure, and in this embodiment, ½ or ¼, and n is the average refractive index of the epitaxial layer.

  Thus, even if the dip shifts to the short wavelength side by etching and deviates from the high reflectance band, a dip corresponding to the next longitudinal mode is generated on the long wavelength side, which further shifts to the short wavelength side. The amount of etching and the etching rate can be managed by measuring the number of dips present in the high reflectance band and the amount of wavelength shift. Therefore, the resonator unit 114 having the predetermined remaining film thickness t in the second cladding layer can be accurately manufactured.

  In addition, since the value and shape of the reflection spectrum can be monitored simultaneously during etching, surface contamination and damage during etching can be evaluated, and the evaluation results can be fed back to the etching conditions.

Further, etching of the SiO ₂ layer by the RIE method will be described as a process using the reflectance monitoring means.

In the manufacturing process of the surface-emitting type semiconductor laser device shown in FIG. 1, as described above, the p-type contact layer 109 on the surface of the resonator is subjected to surface protection until the ring-shaped upper electrode 112 on the laser beam emitting side is formed. It is covered with the SiO ₂ layer I of use (see FIG. 22B), to form the upper electrode must be completely etching the SiO ₂ layer. However, if etching is performed more than necessary, the contact layer is also etched, causing problems that damage the contact layer and change the resonator length related to the oscillation wavelength.

Therefore, management of the etching amount of the SiO ₂ layer is important. Therefore, in this embodiment, a method capable of measuring the reflectance of the epitaxial crystal layer during etching is introduced into the RIE apparatus used for etching the SiO ₂ layer, and the etching amount is measured.

FIG. 33 shows a schematic diagram of a parallel plate RIE apparatus in which reflectance measuring means is introduced. In this RIE apparatus, a mounting electrode 62 connected to an RF oscillator 61 and a mesh-like counter electrode 64 are provided in an etching chamber 60 so as to face each other. A gas supply unit 70 and an exhaust vacuum pump 66 are connected to the etching chamber 60. A window 68 is provided on the wall surface of the etching chamber 60 facing the mounting electrode, and a light source 72 and a photodetector 74 are installed outside the window 68. Then, light having an arbitrary wavelength emitted from the light source 72 reaches the substrate S through the window 68, and the reflected light reaches the photodetector 74 through the window 68. In this RIE apparatus, the SiO ₂ layer is etched by a normal mechanism, and the reflectance or reflection spectrum of the etched surface can be monitored by detecting light from the light source 72.

FIG. 34 shows a change in reflectance with respect to light of 800 nm when the SiO ₂ layer is on the p-type contact layer 109. The horizontal axis represents the film thickness of the SiO ₂ layer, and the vertical axis represents the reflectance. As shown in the figure, the reflectance varies depending on the remaining film thickness of the SiO ₂ layer, and takes a maximum or minimum value every time the remaining film thickness becomes an integral multiple of (λ / 4n). Here, λ is the wavelength of the measurement light source, and n is the refractive index of the SiO ₂ layer. Therefore, the SiO ₂ layer can be completely etched by measuring the reflectance during etching by RIE and monitoring the reflectance curve.

Further, after the complete etching of the SiO ₂ layer, similarly to the RIBE process, the light having a wavelength of, for example, 700 to 900 nm is used by using a light passing through a spectrometer or a wavelength tunable laser beam as a light source for reflectance measurement during RIE. By irradiating light, the reflectance dip can be measured, and the resonator length can be measured. In other words, when etching by RIE is performed while measuring the reflectivity dip, the etching amount can be obtained by the above equation (3), and the resonator length can be accurately controlled. Here, RIE is used because the SiO ₂ layer for protecting the p-type contact layer 109 is completely etched and can be etched in the same apparatus, and the etching rate is higher than the etching by RIBE. It is easy to control the resonator length because it is slow. As etching conditions at this time, for example, an etching pressure of 2 Pa, an RF power of 70 W, and an etching gas CHF ₃ were used. Further, when changing the resonator length of the epitaxial growth film over a wide range, RIE may be performed after the above-described step (a).

As described above, in order to realize the surface emitting semiconductor laser device of the present invention, it is necessary to have a predetermined relationship between the oscillation wavelength determined by the high reflection band of the DBR mirror and the resonator length and the gain offset amount. Even if the relationship does not hold, the resonator length can be accurately adjusted to a predetermined length by etching the contact layer using RIE that monitors the reflectivity, so that a highly accurate device can be manufactured with a high yield. Is possible. This is because the contact layer is an indispensable component in the measurement of the gain spectrum of the active layer, that is, the oscillation spectrum of the edge-emitting semiconductor laser, but the gain spectrum of the active layer includes the p and n-type cladding layers, the active layer, This is because the gain spectrum of the active layer does not change even if the contact layer of the surface emitting semiconductor laser device is etched. That is, by etching the contact layer, it is possible to adjust the lambda _EM without changing the lambda _G.

  Also, by using etching with reflectivity monitoring, it is possible to accurately produce portions having different resonator lengths within the substrate surface, and to produce a surface emitting semiconductor laser device having different oscillation wavelengths on a single substrate. You can also.

(Second embodiment)
FIG. 40A is a perspective view schematically showing a cross section of the light emitting portion of the surface emitting semiconductor laser device according to the second embodiment of the present invention, and FIG. 40B is a plan view of the laser device shown in FIG. 40A.

  The surface emitting semiconductor laser device 300 of this embodiment is characterized in that the optical resonator is composed of a plurality of columnar resonator portions. Since the configuration and operation other than the optical resonator are basically the same as those of the first embodiment, detailed description thereof will be omitted.

That is, the semiconductor laser device 300 has an n-type Al _0.8 Ga _0.2 As layer and an n-type Al _0.15 Ga _0.85 As layer alternately stacked on an n-type GaAs substrate 302 and has a wavelength of about 800 nm. 40 pairs of DBR mirrors 303 having a reflectivity of 99.5% or more for light, an n-type Al _0.7 Ga _0.3 As cladding layer 304, an n ⁻ -type GaAs well layer and an n ⁻ Al _0.3 Ga _{0 .7} Quantum well active layer 305 composed of 21 As barrier layers, p-type Al _0.7 Ga _0.3 As cladding layer 306 and p ⁺ -type Al _0.15 Ga _0.85 As A contact layer 309 is sequentially laminated. Then, the p-type Al _0.7 Ga _0.3 As cladding layer 306 is etched halfway to form a plurality of columnar resonator portions 314 having a rectangular shape when viewed from the top surface of the stacked body, and the periphery thereof is made of SiO _2. A first insulating layer 307 made of a silicon oxide film (SiO _x film) such as the like and a second insulating layer 308 formed on the first insulating layer 307 are embedded.

  In this type of laser device, since the transverse modes of the plurality of separated resonator parts are coupled to each other electromagnetically, the phase-synchronized light is oscillated from each resonator part.

  As shown in FIG. 40B, the columnar resonator portions 314 (314a to 314d) constituting the optical resonator have a rectangular shape in which each cross section parallel to the semiconductor substrate 302 has a long side and a short side, and each resonator portion 314a. It is arrange | positioned so that the direction of the short side of -314d may become parallel, respectively. In this surface-emitting type semiconductor laser device, the polarization plane of the laser light emitted from the plurality of columnar resonator portions 314 coincides with the direction of the short side of each columnar resonator portion 314 having a rectangular cross section. Since the direction of the short side of each of the columnar resonator portions 314 is parallel, the direction of the polarization plane of the laser light emitted from each resonator portion can be made uniform.

Further, as a material constituting the first insulating layer 307 and the second insulating layer 308, for example, a material having a light transmission property such as SiO _x or SiN _x can be used, so that the buried insulating layer can be substantially equal to the laser emission wavelength. It becomes transparent. Therefore, not only the light from the plurality of resonator portions 314 but also the light leaked in the buried insulating layer can effectively contribute to the laser start, and the light emission spot can be widened.

  Next, the relationship between the long side and the short side of the resonator unit 314 will be described in more detail.

  When the length of the long side of each columnar resonator 314 is A and the length of the short side is B, it is preferable that B <A <2B. If the length A is 2B or longer, the shape of the emitted light is not a circle or a regular polygon but a rectangle, so that there is no single light emission spot, and there are a plurality of light emission spots at one emission port. Will be formed. Further, since the volume of the resonator increases, the laser oscillation threshold current also increases.

  Furthermore, each side of the rectangular cross section is preferably set to 1.1 × B ≦ A ≦ 1.5 × B. When the length A of the long side is less than 1.1 × B, the effect of polarization plane control is not sufficiently exhibited. Considering that the laser oscillation threshold current does not increase greatly, it is preferable to set A ≦ 1.5 × B.

  The semiconductor laser device 300 of this embodiment can be manufactured by the same process and apparatus as in the first embodiment except that the mask used when forming the columnar resonator portion 314 is changed. That is, a process similar to that of FIGS. 22A to 22C and FIGS. 23D to 23F can be used except that a mask corresponding to the planar shape of the columnar resonator unit 314 is used as a mask for forming the columnar resonator unit 314. .

  41A to 41D show the shape on the light emitting side and the intensity distribution of NFP during laser oscillation of the conventional surface emitting semiconductor laser and the surface emitting semiconductor laser of this example. FIG. 41A shows a case where the resonator of the conventional surface emitting semiconductor laser shown in FIG. 45 is brought close to about 5 μm, which is a distance that can be embedded with n-p junction GaAlAs epitaxial layers 2207 and 2208. Yes. On the laser emission surface, there are a dielectric multilayer mirror and a p-type ohmic electrode (upper electrode), which are omitted in the figure for comparison of the resonator shapes. FIG. 41B shows the NFP intensity distribution between a and b in FIG. 41A. Even if a plurality of light emitting portions 2220 of a conventional surface emitting semiconductor laser are brought close to the embedding distance, only a plurality of light emitting spots appear, and there is no leakage of light in the lateral direction. It does not become one light emission spot.

  FIG. 41C shows the shape of the surface-emitting type semiconductor laser of this example. The separation groove is buried with a buried insulating layer. When the buried layer is formed by the vapor phase growth method as described above, The small width can be controlled to about 1 μm. FIG. 41D is an NFP between cd in FIG. 41C. Since light is emitted not only from the columnar resonator but also from the separation groove, it can be seen from the NFP that the emission point is widened. Further, since the phases of the laser beams of the resonator units 314a to 314d that are closer to each other are synchronized, the light output is increased and a beam having a radiation angle of 5 ° or less is obtained.

  42A to 42D show an example in which optical resonators having, for example, four resonator portions 314 formed in the second embodiment are arranged at four positions on the semiconductor substrate 302. FIG. In FIG. 42A, an electrode 312 having one light exit port 313 at a position facing four resonator portions 314 is formed for each optical resonator. And the short side (B) in the rectangular cross section of the four resonator parts 314 which comprise each optical resonator is each set to the parallel direction. Therefore, the polarization planes of the respective laser beams emitted from the four light exit ports 313 are aligned in a direction parallel to the short side of the columnar portion having a rectangular cross section.

  FIG. 42B shows a state in which the four laser beams from the semiconductor laser having the four optical resonators pass through the polarization filter 340. Since the four laser beams have the same plane of polarization, they can all pass through the polarizing filter 340.

  FIG. 42C shows a case where the direction of the short side of the columnar resonator unit 314 having a rectangular cross section is different between the two optical resonators, and is set to, for example, directions orthogonal to each other. In this case, as shown in FIG. 42D, one laser beam can pass through the polarizing filter 340, but the other laser beam does not pass through the polarizing filter 340. If this technology is used, only laser light having a polarization plane only in a specific direction can be selectively passed, and can be suitably applied to the field of optical communication.

  In the second embodiment described above, four resonator units are arranged, but the arrangement of the resonator units can be arbitrarily set. For example, as shown in FIGS. 43A to 43C, the resonator units can be arranged at equal intervals in rows and / or columns on a two-dimensional plane parallel to the substrate. Thus, a line beam can be obtained by arranging n resonator units in a line.

  In the second embodiment described above, in order to control the direction of the polarization plane of the emitted laser light, the columnar resonator portion constituting the optical resonator has a rectangular cross-sectional shape. The laser light having the polarization plane aligned in the direction of the short side can also be emitted by forming the light emission port 313 formed in the shape of a rectangle into a rectangular shape. In the example shown in FIG. 44A, the cross-sectional shape of the columnar resonator portion 314 is circular, but the opening shape of the light emission port 313 formed in the electrode is a rectangular shape having a long side a and a short side b. It has become. In this case, the direction of the polarization plane of the emitted laser light coincides with the direction of the short side b of the rectangular light emission port 313.

  Making the opening shape of the light exit port rectangular is easier in terms of process than making the cross section of the columnar resonator portion of the optical resonator rectangular. In addition, when forming an optical resonator having a plurality of columnar resonator portions, the section of each columnar resonator portion may not be rectangular due to the arrangement of the columnar resonator portions. It is effective to set the direction of the plane of polarization by making the exit port rectangular. FIG. 44B and FIG. 44C each show an example in which the cross section of the four columnar resonator portions 314 is a circle or a regular polygon, and a rectangular light emission port 313 is formed in a region facing the columnar resonator portion. In FIG. 44D, each cross section of the four columnar resonator portions 314 is also rectangular, and the opening shape of the light emission port 315 formed in the region facing the four columnar resonator portions is also rectangular. The directions of the short side (B) of the columnar resonator portion having a rectangular cross section and the short side (b) of the light exit port are set in parallel directions.

  When the opening shape of the light exit port is rectangular as described above, when the length of the long side of the light exit port is a and the length of the short side is b, preferably b <a <2 × b. More preferably, 1.1 × b ≦ a ≦ 1.5 × b. The reason for this is that if the ratio of b / a is increased, the ratio B / A of each side of the columnar resonator portion of the optical resonator must be increased accordingly. This is because it falls outside the preferred range.

  Furthermore, as shown in FIG. 44E, the resonator section 314 may have a cross-sectional shape that is a rectangle including a long side (A) and a short side (B), and the light emission port 313 may have a circular shape.

  In the second embodiment described above and the modifications thereof, since the polarization plane of the laser light can be aligned in a specific direction, when the laser apparatus is installed in a device such as a laser printer or a communication device, the laser device is provided. It is possible to easily set the direction of the polarization plane of the laser light in a specific direction without necessarily requiring fine position adjustment.

  In the above-described embodiments, the surface emitting semiconductor laser device using the AlGaAs type semiconductor has been described. However, the present invention is not limited to this, and the present invention is applicable to the surface emitting laser device using the AlGaInP type or InGaAsP type semiconductor. it can. The present invention can also be applied to a surface emitting semiconductor laser comprising a semiconductor layer having a polarity opposite to that of the semiconductor layer of the above-described embodiment.

1 is a perspective view schematically showing a cross section of a surface emitting semiconductor laser device according to a first embodiment of the present invention. 47 is a diagram illustrating IL characteristics and IV characteristics of the surface-emitting type semiconductor laser device shown in FIG. 1 and the conventional surface-emitting type semiconductor laser device shown in FIG. It is a top view of the light emission part of the surface emitting semiconductor laser apparatus shown in FIG. It is a figure which shows the relationship between the injection current and optical output of the surface emitting semiconductor laser apparatus shown in FIG. FIG. 5A is a cross-sectional view schematically showing a surface-emitting type semiconductor laser device for comparison, in which an element etched up to an active layer is shown. FIG. 5B is a cross-sectional view schematically showing the surface-emitting type semiconductor laser device shown in FIG. It is a figure which shows the relationship between the reciprocal number of the resonator diameter of the surface emitting semiconductor laser apparatus shown in FIG. 1, and an oscillation threshold current density. FIG. 2 is a diagram illustrating a relationship between an injection current and an optical output of the surface-emitting type semiconductor laser device illustrated in FIG. 1 and illustrating that this relationship depends on a remaining film thickness t of a cladding layer. It is a figure which shows the relationship between the remaining film thickness t of the clad layer of the surface emitting semiconductor laser apparatus shown in FIG. 1, and the value of external differential quantum efficiency (slope efficiency). FIG. 2 is a diagram showing a relationship between a wavelength and an emission spectrum of light emitted when the thickness of a single quantum well (well) is variously changed in the structure of the active layer of the surface-emitting type semiconductor laser device shown in FIG. . In the structure of the active layer of the surface emitting semiconductor laser device shown in FIG. 1, the relationship between the film thickness of the single quantum well (well) and the emission peak wavelength is shown, and the theoretical value (solid line) and the actual measurement value (dot) are shown. FIG. FIG. 2 is a diagram showing a relationship between a film thickness of a single quantum well (well) and a half-value width of light emission intensity, and a theoretical value and an actual measurement value in the structure of the active layer of the surface emitting semiconductor laser device shown in FIG. It is a figure which shows the relationship between the film thickness of the active layer of the surface emitting semiconductor laser apparatus shown in FIG. 1, and a threshold current density, and shows the theoretical value and measured value. FIG. 2 is a diagram showing the Al composition of each crystal layer in the crystal growth of the surface emitting semiconductor laser device shown in FIG. 1. FIG. 2 is a diagram showing a relationship between an injection current and an optical output of elements having different Al compositions in a clad layer in the surface emitting semiconductor laser device shown in FIG. 1. FIG. 2 is a diagram showing the relationship between the Al composition and the value of external differential quantum efficiency (slope efficiency) when the Al composition of the cladding layer is variously changed in the surface emitting semiconductor laser device shown in FIG. 1. In the surface-emitting type semiconductor laser device shown in FIG. 1, it is a diagram showing the relationship between the injection current and the light output when dielectric materials having different light absorption coefficients are used for the dielectric multilayer mirror. FIG. 17A is a diagram schematically showing a cross section, a resonator length, and a flow of injection current of the surface emitting semiconductor laser device shown in FIG. FIG. 17B is a perspective view schematically showing a cross section of the edge-emitting semiconductor laser device formed by using a part of the semiconductor laminated wafer for forming the surface-emitting semiconductor laser device shown in FIG. FIG. 2 is a diagram showing a reflectance spectrum of a DBR mirror and stacked semiconductor layers of the surface emitting semiconductor laser device shown in FIG. 1 and an oscillation spectrum of an edge emitting semiconductor laser device. FIG. 19A is a diagram showing the relationship between the oscillation wavelength and the case temperature of the edge-emitting semiconductor laser device manufactured using the semiconductor laminated wafer for forming the surface-emitting semiconductor laser device shown in FIG. FIG. 19B is a diagram showing the relationship between the oscillation spectrum and the case temperature of the edge-emitting semiconductor laser device manufactured by using the semiconductor stack for forming the surface-emitting semiconductor laser device shown in FIG. 20A is a diagram showing the relationship between the oscillation wavelength and the case temperature of the surface-emitting type semiconductor laser device shown in FIG. 20B is a diagram showing the relationship between the injection current density, the oscillation wavelength, and the junction temperature increase of the surface-emitting type semiconductor laser device shown in FIG. FIG. 2 is a diagram showing a relationship between a gain offset amount Δλ _BS and an oscillation threshold current of the surface emitting semiconductor laser device shown in FIG. 22A to 22C are cross-sectional views schematically showing a manufacturing process of the surface-emitting type semiconductor laser device shown in FIG. 23D to 23F are cross-sectional views schematically showing a manufacturing process of the surface-emitting type semiconductor laser device shown in FIG. 24A is a diagram showing the far-field image intensity of the emitted light when the resonator portion diameter Da is 8 μm and the light emission port diameter is 6 μm in the surface-emitting type semiconductor laser device shown in FIG. 24B is a diagram illustrating the far-field image intensity when Da is 13 μm and Dw is 10 μm. FIG. 25A is a diagram showing an emission near-field image and a light intensity distribution at line aa when the thickness of the p-type cladding layer is 1.0 μm in the surface-emitting type semiconductor laser device shown in FIG. FIG. 25B is a diagram showing a light emission near-field image when the thickness of the p-type cladding layer is 0.3 μm, and a light intensity distribution in the line bb. It is a figure which shows the influence of the film thickness of a p-type cladding layer on the relationship between the injection current and optical output of the surface emitting semiconductor laser apparatus shown in FIG. It is a figure which shows the influence of the film thickness of a p-type cladding layer on the relationship between the injection current and optical output in the surface emitting semiconductor laser apparatus shown in FIG. It is a figure which shows the film thickness distribution of the semiconductor laminated wafer obtained in the process which manufactures the surface emitting semiconductor laser apparatus concerning 1st Example of this invention. It is sectional drawing which shows typically the MOVPE apparatus used when forming the DBR mirror of the surface emitting semiconductor laser apparatus shown in FIG. It is a figure which shows the relationship between the growth time of an epitaxial layer, and a reflectance in the process of forming the DBR mirror of the surface emitting semiconductor laser device shown in FIG. FIG. 2 is a cross-sectional view schematically showing a RIBE apparatus used in the manufacturing process of the surface-emitting type semiconductor laser device shown in FIG. 1. 32A to 32C are diagrams showing changes in the reflection spectrum in the RIBE process. It is sectional drawing which shows typically the RIE apparatus used in the etching process of the surface emitting semiconductor laser apparatus shown in FIG. Is a diagram showing the film thickness of the SiO ₂ layer and the reflectance of the relationship when performing RIE using the apparatus shown in FIG. 33. FIG. 35 is a timing chart showing changes in the flow rates of TMGa, TMAl, and H ₂ Se when a DBR mirror constituting the surface-emitting type semiconductor laser device shown in FIG. 1 is formed. It is a figure which shows the result of having evaluated a part of DBR mirror of the surface emitting semiconductor laser apparatus shown in FIG. 1 by the SIMS method. FIG. 37A shows a band when the concentration of Se is sharply increased near the interface with the n-type Al _0.1 Ga _0.9 As layer in the n-type Al _0.7 Ga _0.3 As layer in the DBR mirror. FIG. FIG. 37B is a diagram showing a band when Se is created at a constant supply amount. FIG. 3 is a timing chart showing changes in the flow rate of TMAl and irradiation with ultraviolet light in a manufacturing process of a DBR mirror constituting the surface-emitting type semiconductor laser device shown in FIG. It is a figure which shows the result of having evaluated a part of DBR mirror obtained by the process of FIG. 1 by the SIMS method. FIG. 40A is a perspective view schematically showing a cross section of the surface emitting semiconductor laser device according to the second embodiment of the present invention. FIG. 40B is a plan view of the apparatus shown in FIG. 40A as viewed from the light emitting side. FIG. 41A shows the shape of the resonator part on the side from which light of the conventional surface emitting semiconductor laser device is emitted, and FIG. 41B shows the intensity distribution of the near-field emission image of the laser device shown in FIG. 41A. FIG. 41C shows the shape of the resonator on the light emitting side in the second embodiment, and FIG. 41D shows the intensity distribution of the light emission near-field image of the laser device shown in FIG. 41C. FIG. 42A shows an example in which the optical resonators of the surface-emitting type semiconductor laser device according to the second embodiment are arranged at a plurality of locations, and FIG. 42B shows that the laser light emitted from the optical resonators is passed through the polarization filter. Indicates the state. FIG. 42C shows a state in which the optical resonators of the surface-emitting type semiconductor laser device according to the second embodiment are arranged in different directions, and FIG. 42D shows the laser light emitted from the optical resonators shown in FIG. The state passed through is shown. FIG. 43A to FIG. 43C are views showing a state in which resonator portions having a rectangular shape with a short side and a long side are arranged in rows and / or columns on a two-dimensional plane parallel to the substrate. 44A to 44D are diagrams illustrating a resonator that controls the direction of the polarization plane of the laser light by forming the light emission port in a rectangular shape. FIG. 44E is a diagram showing a resonator in which the cross-sectional shape of the resonator portion is rectangular and the shape of the light emission port is circular. It is a perspective view which shows an example of the conventional surface emitting semiconductor laser apparatus. It is sectional drawing which shows the prior art example of another surface emitting semiconductor laser apparatus. It is a figure which shows the relationship between injection current when changing the number of layers of an active layer, and optical output. It is a figure which shows typically the relationship between the film thickness of the well layer and barrier layer in an active layer, and Al composition.

Explanation of symbols

100 surface emitting semiconductor laser, 101 metal layer for electrode (lower electrode), 102 n-type GaAs substrate, 103 DBR mirror, 104 first cladding layer, 105 quantum well active layer, 106 second cladding layer, 107 first Insulating layer, 108 Second insulating layer, 109 Contact layer, 110 First direction, 111 Dielectric multilayer mirror, 112 Contact metal layer (upper electrode), 113 Opening, 114 Resonator

Claims (4)

A substrate made of a compound semiconductor of the first conductivity type,
A lower electrode formed on the lower side of the substrate;
A mirror formed on the upper side of the substrate;
A first cladding layer of a first conductivity type formed on the mirror;
A quantum well active layer formed on the first cladding layer;
A second cladding layer of a second conductivity type formed on the quantum well active layer and having one or more columnar parts;
A second conductivity type contact layer formed on the columnar portion of the second cladding layer;
A columnar portion of the second cladding layer and a buried insulating layer buried around the contact layer, and an opening facing a part of the contact layer, both in the contact layer and the buried insulating layer An upper electrode formed across,
Including
The peak wavelength λ _G of the gain spectrum of the quantum well active layer is set to a short wavelength side by a predetermined wavelength difference (gain offset amount) Δλ _{BS with} respect to the intended oscillation wavelength λ _EM , and the gain offset amount Δλ _BS Is a surface emitting semiconductor laser device having a thickness of 5 to 20 nm when measured near a temperature at which the surface emitting semiconductor laser device is used. In claim 1,
The surface-emitting type semiconductor laser device, wherein the buried insulating layer includes a first insulating layer made of a silicon compound covering at least an interface between the second cladding layer and the contact layer. In claim 2,
The buried insulating layer includes the first insulating layer and a second insulating layer formed on the first insulating layer and for planarizing the columnar portion of the second cladding layer and the periphery of the contact layer. Surface emitting semiconductor laser device. A method of manufacturing a surface-emitting type semiconductor laser device including the following steps (a) to (d).
(A) On a substrate made of a first conductive type compound semiconductor, at least a mirror, a first conductive type first cladding layer, a quantum well active layer, a second conductive type second cladding layer, and a second conductive type Forming a semiconductor layer including a contact layer by epitaxial growth;
(B) etching the contact layer and the second cladding layer to form one or more columnar portions;
(C) forming a buried insulating layer around the columnar part; and (d) having an opening facing a part of the contact layer and straddling both the contact layer and the buried insulating layer. Forming an upper electrode;
Including
The semiconductor layer is set such that the peak wavelength λ _G of the gain spectrum of the quantum well active layer is shorter than the intended oscillation wavelength λ _EM by a predetermined wavelength difference (gain offset amount) Δλ _BS , The gain offset amount Δλ _BS is 5 to 20 nm when measured near the temperature at which the surface emitting semiconductor laser device is used.

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