WO2004027950A1 - 半導体レーザ - Google Patents
半導体レーザ Download PDFInfo
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- WO2004027950A1 WO2004027950A1 PCT/JP2003/011488 JP0311488W WO2004027950A1 WO 2004027950 A1 WO2004027950 A1 WO 2004027950A1 JP 0311488 W JP0311488 W JP 0311488W WO 2004027950 A1 WO2004027950 A1 WO 2004027950A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S2301/00—Functional characteristics
- H01S2301/18—Semiconductor lasers with special structural design for influencing the near- or far-field
Definitions
- the present invention relates to a semiconductor laser.
- the semiconductor laser of the present invention is applicable to all kinds of semiconductor lasers whose oscillation wavelength changes depending on current Z, optical output Z, temperature, and the like. Background art
- optical information processing technology and optical communication technology has been remarkable. For example, to realize two-way communication over an optical fiber network at high speed and with a large amount of information such as image information, a large-capacity optical fiber transmission line and a signal with flexibility for the transmission method An amplifier for amplification is indispensable.
- EDFAs optical fiber amplifiers
- Er 3+ rare earths
- the wavelength of semiconductor lasers is becoming shorter for high-density recording. Remarkable especially recent developments of the blue laser, grown on a substrate, such as A 10 x The reliability of the selected GaN-based materials has also increased, and further research is ongoing. Furthermore, semiconductor lasers have been applied to the medical field, precision processing field, and the like, and the range of application has been expanding.
- semiconductor lasers have advantages in many applications in that they are smaller and lighter than solid state lasers and gas lasers.
- its wavelength stability is not always superior to other laser light sources.
- the oscillation wavelength generally becomes longer as the element temperature rises. This is because the band gap of the material constituting the semiconductor laser is reduced at high temperatures, and it can be said that it is basically a characteristic inherent to the constituent material.
- the semiconductor laser in a 980 nm band semiconductor laser, is formed on a substrate that is transparent to the oscillation wavelength, and When the refractive index is relatively larger than that of the cladding layer, that is, under the intentionally formed semiconductor laser waveguide, there is a substrate exhibiting a waveguide function, and the laser waveguide and the substrate waveguide are provided.
- the waveguides are coupled, (1) the intensity independent of the Fabry-Low mode spacing determined by the resonator length of the element is shown in the oscillation spectrum of the element depending on the thickness of the substrate. If modulation is observed (Fig. 4 in the literature), and (2) the thickness of the normal substrate (about 120 ⁇ ), the intensity modulation period will be about 2.5 nm.
- the document also discusses this wavelength stabilizing mechanism.
- a gain spectrum generated by injecting a current into a waveguide formed as a semiconductor laser moves to a longer wavelength side when an injection current / optical output / temperature is increased. This is the reason for the wavelength change in ordinary semiconductor lasers.
- the semiconductor laser is formed on a substrate that is transparent to the oscillation wavelength and the refractive index of the substrate is relatively larger than that of the cladding layer, the wavelength change will occur.
- the mechanism that suppresses the occurrence is caused in the substrate. Since stimulated emission does not occur on the substrate that functions as a waveguide, the injected carriers are accumulated.
- the refractive index of a semiconductor material decreases as the carrier density increases. This phenomenon is known as the plasma effect.
- the intensity modulation in the oscillation spectrum generated as a result of the coupling between the laser waveguide and the substrate waveguide, and the longitudinal mode selected as a result have a mechanism for shortening the wavelength by current injection. It will be. That is, the wavelength stabilization region shown in FIG. 7 of the IEEE Journal is shortened by the effect of the gain spectrum attached to the laser waveguide, which has a longer wavelength as a result of current injection, and the plasma effect. It can be understood that this is the result realized by the “balance” of the effects derived from the substrate waveguide.
- the region where the wavelength is stabilized with respect to the current change is narrow, and the very large wavelength change before and after the stabilized region.
- There are problems such as the occurrence of a dangling.
- An object of the present invention is to solve the above-mentioned problems of the prior art. Specifically, the present invention reduces the current dependency, light output dependency, or temperature dependency of the oscillation wavelength of a semiconductor laser in a relatively wide current / light output range or temperature range by a simple method. The aim was to provide a method.
- the present inventors have carried out intensive investigations and found that the means for solving such problems, at least, a substrate, a first conductivity type cladding layer average refractive index of N Lcld, the average refractive index of N A active layer structure, the average refractive A semiconductor laser having an oscillation wavelength X (nm) having a second conductivity type cladding layer having an N 2cld ratio, wherein the first conductivity type is provided between the substrate and the first conductivity type cladding layer.
- Has an average refractive index of secondary waveguide layer is N Lsff6, Kakatsu, between the sub waveguide layer and the substrate, the low refractive index layer having an average refractive index indicates the first conductivity type is a New 1Iotaramuda It has been found that the problem can be solved by the present invention relating to a semiconductor laser characterized by having a refractive index satisfying all of the following expressions.
- Preferred embodiments of the present invention include the following. First, it is preferable that the refractive index satisfies all of the following expressions.
- the thickness T Lcld of the first conductivity type cladding layer of the semiconductor laser of the present invention (nm) and the thickness T of the second-conductivity-type cladding layer 2Cld (nm) satisfies the following formula are preferred.
- the thickness T lsre (nm) of the first conductivity type sub-waveguide layer of the semiconductor laser of the present invention preferably satisfies the following expression.
- the thickness T 1UL (nm) of the first conductivity type low refractive index layer of the semiconductor laser of the present invention preferably satisfies the following expression.
- the substrate thickness T sub (nm) of the semiconductor laser of the present invention satisfies the following expression.
- the substrate has an oscillation wavelength l (nm). In this case, it is desirable that the substrate satisfy the following expression when the refractive index of the substrate is N sub . In another preferred embodiment of the present invention, the substrate absorbs an oscillation wavelength (nm).
- a preferred embodiment of the semiconductor laser of the present invention is an edge-emitting device having an edge-reflection type resonator structure.
- a first light guide having a refractive index of NG is provided between the first conductivity type cladding layer and the active layer structure, and the first and second active layer structures have the same structure as the active layer structure.
- the refractive index of the substrate at the oscillation wavelength ⁇ (nm) of the laser is NS (B )
- a substrate satisfying at least one of the following expressions is particularly preferable.
- the conductive type clad layer is divided into two layers, the second conductive type upper clad layer and the second conductive type lower clad layer, and a current injection region is formed by the second conductive type upper clad layer and the current blocking layer.
- Examples include a contact layer.
- the above-described semiconductor laser of the present invention preferably operates in a single transverse mode. Further, in the semiconductor laser of the present invention, it is preferable that the first conductivity type is n-type and the second conductivity type is p-type.
- FIG. 1 shows an example of the basic layer structure of the semiconductor laser of the present invention in the center of FIG. 1, an example of the refractive index distribution according to the present invention on the left of FIG. 1, and the light intensity expected in the present invention on the right of FIG.
- FIG. 1 shows an example of the distribution, and the directions of the words vertical, horizontal, and Z resonator directions used in this specification are shown in FIG.
- FIG. 2 is a schematic sectional view of an example of the semiconductor laser of the present invention.
- FIG. 3 is an oscillation spectrum of the semiconductor laser of the embodiment.
- FIG. 4 is a diagram showing the current dependence of the wavelength of the longitudinal mode showing the maximum intensity in the oscillation spectrum of the semiconductor laser of the example.
- FIG. 5 is an oscillation spectrum of the semiconductor laser of Comparative Example 1.
- FIG. 6 is a diagram showing the current dependence of the wavelength of the longitudinal mode showing the maximum intensity in the oscillation spectrum of the semiconductor laser of Comparative Example 1.
- FIG. 7 is an oscillation spectrum of the semiconductor laser of Comparative Example 2.
- FIG. 8 is a diagram showing the current dependence of the wavelength of the longitudinal mode showing the maximum intensity in the oscillation spectrum of the semiconductor laser of Comparative Example 2.
- 1 is a substrate
- 2 is a first conductivity type low refractive index layer
- 3 is a first conductivity type sub-waveguide layer
- 4 is a first conductivity type cladding layer
- 5 is an active layer structure
- 6 is a second conductivity type.
- Clad layer, 7 is the second conductivity type contact layer
- 11 is the first conductivity type substrate
- 12 is the first conductivity type buffer layer
- 13 is the first conductivity type low refractive index layer
- 14 is the first conductivity type Sub waveguide layer
- 15 is a first conductivity type cladding layer
- 16 is a first light guide layer
- 17 is an active layer structure
- 18 is a second light guide layer
- 19 is a lower conductive layer of the second conductive type
- 20 is a current block layer of the first conductive type
- 21 is a cap layer
- 22 is an upper clad layer of the second conductive type
- 23 is a contact layer of the second conductive type.
- 101 is a strained quantum well layer
- 102 is a barrier layer
- 103 is a strained quantum well layer
- 201 is a substrate side (first conductivity type side) electrode
- 202 is an epitaxy layer side ( (Second conductivity type side) electrode.
- the semiconductor laser of the present invention is not particularly limited in its structural details and manufacturing method as long as it satisfies the conditions of claim 1.
- a range including A and B indicates a range including A and B.
- FIG. 1 shows an example of the refractive index distribution according to the present invention. In general, high refractive index semiconductor materials tend to have a narrow band gap, and the same picture also shows the band gap axis. Further, on the right side of FIG. 1, an example of the light intensity distribution expected in the present invention is shown. In addition,
- laser waveguide a portion having the function of a normal semiconductor laser composed of the first conductivity type clad layer Z active layer structure Z second conductivity type clad layer is referred to as “laser waveguide”. It shall be.
- the laser waveguide portion according to the present invention is basically the same as the conventional device.
- the first conductivity type sub-waveguide layer is intentionally arranged on the first conductivity type substrate side of the first conductivity type clad layer. Since the first conductive type sub-waveguide layer is sandwiched between the first conductive type clad layer having a relatively low refractive index and the first conductive type low refractive index layer, it becomes a layer having a waveguide function. . Furthermore, since the first conductivity type low refractive index layer / first conductivity type sub-waveguide layer / first conductivity type cladding layer are all of the same conductivity type, the sub-waveguide layer is a waveguide having gain like an active layer. Instead, it becomes a waveguide having a passive function.
- the first conductive type low refractive index layer Z The first conductive type sub-waveguide layer Z
- the passive waveguide part composed of the first conductive type clad layer is described as ⁇ sub-waveguide '' I decided to.
- This sub-waveguide is such that the function as a waveguide of the substrate disclosed by the present inventor in the IEEE Journal is independently controlled as a layer structure that is intentionally grown epitaxially so as to be controllable. It is possible to understand. Therefore, the wavelength stability of the semiconductor laser according to the present invention is that the increase in the wavelength of the gain spectrum due to current injection is suppressed by the plasma effect in which the refractive index of the first conductive type sub-waveguide layer is reduced. It is. Regarding the temperature dependence, the oscillation wavelength caused by the thermally increased refractive index of the first conductivity type sub-waveguide layer is more than the longer oscillation wavelength caused by the reduction of the bandgap of the active layer due to the temperature rise.
- the present invention Since the effect of increasing the wavelength is smaller, it is possible to suppress the increase in the wavelength of the gain spectrum generated in the laser waveguide. Furthermore, in the present invention, by changing the thickness of the first conductive type sub-waveguide layer that is epitaxially grown, the width of the current injection region where the wavelength is stable as shown in FIG. It is possible to change. As for the temperature dependence, it is possible to enlarge the relatively small temperature dependence area shown in Fig. 11 in the IEEE Journal. Specifically, since there is an inverse relationship between the thickness of the sub-waveguide layer and the period of the intensity modulation observed in the oscillation spectrum of the element, for example, the present invention is applied to the first conductivity type sub-waveguide.
- the intensity modulation period can be expected to be about 15 nm.
- the longitudinal mode showing the maximum intensity is, for example, Even if the gain spectrum of the semiconductor laser shifts to the longer wavelength side with the injection current, it does not easily shift to the adjacent longitudinal mode. For this reason, the oscillation wavelength of the element can be expected to be stabilized over a wider current width than when the oscillation wavelength is stabilized by the effect of a thick substrate waveguide of, for example, about 120 ⁇ .
- the thickness of the first conductivity type sub-waveguide layer it is possible to set the substantial intensity modulation period to be wider than the spread of the gain spectrum of the semiconductor laser. In this case, only one longitudinal mode selected as a result of the intensity modulation appears in the oscillation spectrum of the element, and the intensity modulation period is not apparently observed. This means that a semiconductor laser with extremely excellent monochromaticity can be manufactured.
- a feature of the present invention is that the passive waveguide function is independent of the substrate, and the wavelength stabilization as shown in FIG. 7 of the IEEE Journal is performed without depending on the relative relationship between the substrate and the oscillation wavelength.
- This makes it possible to form the active region with a wide-area current injection region.
- it is important to sufficiently suppress the amount of light propagating in the sub-waveguide layer leaking into the first conductivity type substrate, and as shown in FIG.
- the first-conductivity-type low-refractive-index layer disposed between the substrate and the first-conductivity-type sub-waveguide layer prevents the laser waveguide and the sub-waveguide coupled to each other from being optically coupled to the substrate. It has an important role to play.
- the characteristics as shown in FIG. 7 or FIG. 11 in the IEEE Journal indicate that the substrate is transparent to the oscillation wavelength and the refractive index of the substrate is clad.
- a layer higher than that of the layer that is, under the intentionally formed semiconductor laser waveguide, there is a substrate exhibiting a waveguide function, and the laser waveguide and the substrate waveguide are provided. It does not appear unless there is a specific situation such as the coupling of the wave paths.
- An example is a 980 nm band semiconductor laser formed on a GaAs substrate and having a relatively thin cladding layer and an InGaAs active layer.
- an AlGaAs active layer formed on a GaAs substrate in which the band gap of the substrate is smaller than the oscillation wavelength of the element and the substrate is an absorber for the oscillation wavelength is provided.
- the degree of coupling between the laser waveguide and the sub-waveguide can be adjusted by the thickness of the cladding layer of the first conductivity type and the relative refractive index between the laser waveguide and the sub-waveguide.
- a second conductivity type cladding layer having a refractive index waveguide structure and having a conductivity type different from that of the substrate is used.
- the upper cladding layer and the lower cladding layer of the second conductivity type are divided into two layers, and the upper cladding layer of the second conductivity type and the current blocking layer form a current injection region.
- the present invention will be described in detail using an element having a single contact mode and capable of operating in a single transverse mode.
- the first conductivity type is described as n-type
- the second conductivity type is described as p-type.
- each layer is not limited to the present invention, and a part of each layer may be undoped and a part may be of the first conductivity type or the second conductivity type.
- the refractive index of each layer is the refractive index in the oscillation oscillation of the element, and that the layer exhibiting a certain function is composed of a plurality of layers.
- the refractive index of the layer shall be given as the average obtained by dividing the sum of the products of the refractive index and the thickness of each layer constituting the layer by the sum of the thicknesses.
- the present invention is particularly effective in a semiconductor laser operating in a single transverse mode. This is, This is because the monochromaticity of the oscillation spectrum of a device operating in a single transverse mode is much better than that of a device without a transverse mode control function.
- the substrate of the first conductivity type (11) has a desired oscillation wavelength, lattice matching, distortion intentionally introduced into the active layer, etc., and distortion compensation of the active layer used for the guide layer, etc.
- a GaAs, InP, GaN single crystal substrate or the like is used.
- a substrate not only a just substrate, but also a so-called off-substrate (miss-oriented substrate) can be used from the viewpoint of improving crystallinity during epitaxial growth.
- the off-substrate has the effect of promoting crystal growth in a step-to-step mode, and is widely used.
- the off-substrate having an inclination of about 0.5 to 2 degrees is widely used, but the inclination may be about 10 degrees depending on the material system constituting the quantum well structure.
- the substrate may be subjected to chemical etching or heat treatment in advance in order to manufacture a semiconductor laser using a crystal growth technique such as MBE or MOCVD.
- the present invention can be arbitrarily applied whether the substrate absorbs light having the oscillation wavelength defined by the active layer structure or the substrate is transparent. This is because it is not necessary to consider the optical characteristics of the substrate by the first conductivity type low refractive index layer described later. For this reason, the final thickness of the substrate can be set within a range that ensures sufficient mechanical strength when manufacturing a semiconductor laser structure and that does not impair cleavage or the like. 135 m, preferably 95 to 125 / im.
- the buffer layer (1 2) also preferably exhibits the first conductivity type.
- the buffer layer (12) can reduce the imperfections of the Balta crystal and have the same crystal axis. Preferably, it is provided to facilitate the formation of a thin film.
- the first conductivity type buffer layer is preferably composed of the same compound as the first conductivity type substrate. In the case of a As, Ga As is usually used. In this case, the buffer layer can be treated optically in the same way as the substrate. However, the use of a superlattice layer for a buffer layer is widely practiced, and may not be formed of the same compound. You. In some cases, a material different from that of the substrate is selected for the buffer layer depending on the desired emission wavelength and the structure of the entire device.
- the function of the first conductivity type low refractive index layer can be realized by a buffer layer made of a structure or a material different from such a substrate.
- the refractive index N BUI of the buffer layer with respect to the oscillation wavelength may be treated equivalently to the refractive index N of the first conductivity type low refractive index layer.
- the first-conductivity-type low-refractive-index layer (13) is disposed between the substrate and the first-conductivity-type sub-waveguide layer, realizes confinement of light in the sub-waveguide layer, and optically interacts with each other.
- the sub-waveguide (consisting of the first conductive type low refractive index layer / first conductive type sub-waveguide layer / first conductive type clad layer) is not optically coupled to the first conductive type substrate. It has an important role to play.
- the refractive index N I for the oscillation wavelength of the first conductivity type low refractive index layer is different from the refractive index N 1S of the sub-waveguide.
- the refractive index of the first conductivity type cladding layer is NLCLD and the refractive index of the second conductivity type cladding layer is N2CLD ,
- the refractive index N2CLD of the second conductivity type cladding layer is the same as the refractive index of each layer. It is given as the average of the sum of the products of the thicknesses divided by the sum of the thicknesses. Further, when the substrate of the first conductivity type is transparent to the oscillation wavelength and the refractive index thereof is NSUB , it is preferable that the following condition is satisfied.
- the thickness of the first-conductivity-type low-refractive-index layer realizes confinement of light in the sub-waveguide layer, and allows the laser waveguide and the sub-waveguide optically coupled to each other to be connected to the first-conductivity-type substrate. It can be appropriately selected so as not to be optically coupled.
- the thickness T i (nm) is 500 (nm) ⁇ T 1 LIL ⁇ 200 000 (nm)
- the first conductivity type low refractive index layer may have a single layer low refractive index layer, but may have a superlattice structure in which a layer structure sufficiently thinner than the oscillation wavelength is laminated.
- the first-conductivity-type sub-waveguide layer (14) is located between the first-conductivity-type low-refractive-index layer and the first-conductivity-type cladding layer, and the light that has appropriately leaked from the first-conductivity-type cladding layer. It has the function of guiding light. To realize this function, the refractive index of the first conductivity type sub-waveguide layer
- N LSWE is the refractive index of the first conductivity type low refractive index layer N 1 UL and the refractive index of the first conductivity type cladding layer N LCLD.
- the refractive index of the second conductivity type cladding layer constituting the laser waveguide is different from that of N2CLD.
- the thickness of the first conductivity type sub-waveguide layer depends on the width of the region where the oscillation wavelength is desired to be stabilized against the current change of the element, the oscillation wavelength of the element, the material of the first conductivity type sub-waveguide layer itself, and the like. Thus, it can be appropriately selected. Generally, as a result of the coupling between the laser waveguide and the sub-waveguide, the period of intensity modulation seen in the oscillation spectrum is inversely proportional to the thickness of the first conductivity type sub-waveguide layer. In a semiconductor laser having a cavity, the thickness T 1SffG (nm) of the sub-waveguide layer of the first conductivity type is
- the mode to be performed is often a higher-order mode having a relatively high order, considering the oscillation wavelength of the element.
- the whole or a part thereof can be composed of a superlattice or the like. Further, it is possible in principle to partially or entirely make the first conductive type sub-waveguide layer undoped.
- the first-conductivity-type cladding layer (15) is a component that constitutes the laser waveguide and the sub-waveguide, and also has a role of adjusting the coupling between these two waveguides.
- the refractive index N lcld of the first conductivity type cladding layer must be different from the average refractive index N A of the active layer structure.
- the refractive index N lsffe of the first conductivity type sub-waveguide layer is
- the thickness T lcld (nm) of the first conductivity type cladding layer can be appropriately selected so that the two waveguides are coupled in the relative relationship between the laser waveguide and the sub-waveguide. In order to realize the weak coupling, it is necessary to increase the thickness. From this point of view, the thickness specified at the oscillation wavelength ⁇ (nm)
- the first conductivity type cladding layer can be partially undoped, and the doping level can be changed within the layer.
- the first-conductivity-type cladding layer and the second-conductivity-type cladding layer need not be composed of a single layer in order to realize various optical confinements in the laser waveguide, but are composed of a plurality of layers. No problem. Further, the first conductivity type cladding layer may have a part having a super lattice structure or the like.
- the active layer structure in the present invention refers to a single Balta active layer, a single quantum well active layer, or a double quantum well structure in which two quantum well active layers are separated by a barrier layer.
- a multiple quantum well structure or the like in which one or more quantum well active layers are separated by barrier layers.
- a light guide layer is used for an active layer structure having a quantum well layer.
- the light guide layer is not included in the concept of the active layer structure.
- Active layer structure (17) is first conductivity type cladding layer, it is necessary to configure the laser waveguide with the second-conductivity-type cladding layer, an average refractive index N A of the active layer structure of a first conductivity type cladding layer refractive index N leld, must satisfy the relation below with the refractive index 2cld of the second conductivity type cladding layer.
- the active layer structure preferably includes a quantum well active layer rather than a Balta active layer, because it is more suitable for increasing the output of the device and the like.
- the substrate is GaAs, the A1GaAs quantum well layer, the InGaP quantum well layer, the InGaAs strained quantum well layer, and the InA1GaAs strained quantum well layer
- the structure has layers.
- a strained quantum well layer active layer in which a compressive stress such as InGaAs or InAlGaAs is embedded a decrease in the threshold current of the device can be expected, which is very desirable.
- the substrate is InP
- the substrate has a structure having an InGaAsP quantum well layer and an InAlGaAs quantum well layer.
- the conductivity type of the active layer structure can be set arbitrarily.
- the quantum well layer is undoped and the barrier layer contains a portion containing Si having the first conductivity type. If you want to, In such a case, electrons are supplied from the Si doped in the barrier layer to the quantum well layer, and the gain spectrum of the device is broadened.
- the configuration of the active layer structure and the thickness of each layer constituting the active layer structure can be arbitrarily set.
- the first light guide layer and the second light guide layer constitute a laser waveguide together with the first conductive type clad layer / active layer structure Z and the second conductive type clad layer. If the refractive index of the first light guide layer is N lffle and the refractive index of the second light guide layer is N 2WG
- the refractive index of the first light guide layer and the second light guide layer is different from the refractive index of the first conductivity type sub-waveguide layer.
- the first light guide layer and the second light guide layer have the same refractive index because of the symmetry of the waveguide, and the respective refractive indexes are the same in relation to the first conductivity type sub-waveguide layer. It is desirable.
- the first optical guide layer and the second optical guide layer are both composed of GaAs. Is desirable. The power of these things
- the device can be easily manufactured.
- the thicknesses of the first light guide layer and the second light guide layer can be arbitrarily set, and are appropriately determined in consideration of the state of light confinement in the laser waveguide.
- These light guide layers are not limited to a single layer but may have a structure such as a superlattice or the like and may be composed of a plurality of layers.
- the refractive index of the optical guide layer may be changed within the layer within an appropriate range.
- the conductivity type of the optical guide layer can be set arbitrarily, but it is desirable that there is a portion containing Si that indicates the first conductivity type.
- the second conductivity type cladding layer is used. It is desirable to form a current injection region by using a lower cladding layer and an upper cladding layer in a two-layer structure, and to form a current injection region by the upper cladding layer and the current blocking layer.
- the method of the present invention for stabilizing the oscillation wavelength with respect to current and temperature is particularly effective for an element having a Fabry-Perot resonator and oscillating in a single transverse mode.
- the lower cladding layer of the second conductivity type (19) and the upper cladding layer of the second conductivity type (22) are composed of a first conductivity type cladding layer, a first light guide layer / active layer structure, and a second light guide layer. Construct a waveguide. For this reason, the refractive index N 2cld of the second conductivity type cladding layer is different from the average refractive index N A of the active layer structure.
- the refractive index N 2cld of the second conductivity type cladding layer is different from the refractive index of each layer. It is given as the average of the sum of the thickness products divided by the sum of the thicknesses. Further, the thickness of the second conductivity type cladding layer, that is, the sum T 2cld (nm) of the thicknesses of the lower cladding layer and the upper cladding layer can be appropriately selected. Since it is desired to minimize the exudation of light to the contact layer and the like formed thereon, the thickness T lcld (nm) of the first conductivity type cladding layer is
- the refractive index of the first conductivity type cladding layer Nold and the refractive index of the second conductivity type cladding layer N2cld are the refractive index of the first conductivity type cladding layer Nold and the refractive index of the second conductivity type cladding layer N2cld.
- a part of the second conductivity type cladding layer can be undoped, and the doping level can be changed in the layer.
- the first-conductivity-type clad layer / second-conductivity-type clad layer does not need to be composed of a single layer in order to realize various optical confinements in the laser waveguide, and may be composed of multiple layers. Absent.
- the second conductivity type cladding layer may have a superlattice structure or the like.
- the first conductivity type current block layer (20) literally blocks the current and substantially limits the current injection region, and appropriately adjusts the relative refractive index and the like of the second conductivity type cladding layer. By setting, it has two functions of realizing light confinement in the horizontal direction. -For the former purpose, it is preferable that the conductivity type be the same as that of the first conductivity type cladding layer or be undoped.
- one way to achieve single transverse mode operation with an element structure as shown in Fig. 2 is to make the refractive index of the current block layer smaller than that of the upper cladding layer of the second conductivity type. That is, a waveguide structure in the lateral direction is set in the device.
- the second conductivity type upper cladding layer is composed of Al x Gai — and the current block layer is In the case of, it is possible to realize lateral light confinement by setting X to Z. In this case, it is mainly due to the refractive index difference between the current blocking layer and the second conductivity type upper cladding layer.
- the effective refractive index difference in the lateral direction defined Te is desirably on the order of 10- 3.
- the current block layer may be made of a material that absorbs the oscillation wavelength of the device, and a loss guide type device may be used.
- the width of W in Fig. 2 corresponds to the width of the current injection region.
- the width of W is desirably about 1.5 ⁇ to about 3.5 ⁇ .
- cap layer (21) on the current blocking layer.
- the material for the cap layer is selected so as to protect the current blocking layer in device fabrication and to facilitate the growth of the second conductive type upper cladding layer contact layer.
- the conductivity type of the cap layer may be basically the first conductivity type or the second conductivity type.
- the contact layer is usually made of a GaAs material. This layer usually has a higher carrier concentration than the other layers in order to lower the contact resistivity with the electrode. The thickness of the contact layer is appropriately selected.
- each layer constituting the semiconductor laser is appropriately selected within a range in which the function of each layer is effectively performed.
- an appropriate crystal growth method can be selected according to the thickness.
- the entire device can be manufactured by the MBE or M0CVD method.However, especially when the appropriate thickness exceeds 1 ⁇ when manufacturing a sub-waveguide layer, such a layer can be selectively used. Can be produced by the LPE method or the like.
- an epitaxial layer side electrode (202) is further formed. This can be formed by sequentially depositing, for example, Ti / Pt / Au on the surface of the second conductivity type contact layer and then performing an alloying treatment. Generally, in the steps described so far, a semiconductor laser fabrication process can be performed using a substrate having a thick film of about 350 ⁇ . Before forming the substrate-side electrode, the semiconductor laser is applied to the first conductive type substrate. The surface which has not been manufactured is removed by an appropriate thickness by polishing or the like. In the present invention, the thickness of the entire element can be set to such a degree that the mechanical strength is sufficiently ensured and the cleavability and the like are not impaired.
- a substrate-side electrode (201) is formed. This is formed on the surface of the first conductive type substrate, and in the case of an ⁇ -type electrode, for example, AuGe / Ni / Au is sequentially deposited on the substrate surface and then formed by alloying. Is done.
- an end surface which is a light emission surface is formed on the manufactured semiconductor wafer.
- the light emission is not limited to the edge emission, but is preferably used for an edge emission type device.
- the end face becomes a mirror constituting a resonator.
- the end face is preferably formed by cleavage. Cleavage is a widely used method, and the end face formed by cleavage varies depending on the orientation of the substrate used. For example, when an element such as an edge-emitting laser is formed using a substrate having a plane which is crystallographically equivalent to the nominally (100) which is preferably used, (110) or The plane crystallographically equivalent to this is the plane that forms the resonator.
- the end face may not be 90 degrees with the resonator direction depending on the relationship between the inclined direction and the resonator direction.
- the end face when a substrate whose angle is tilted by 2 degrees from the (100) substrate toward the (1-100) direction is used, the end face also tilts by 2 degrees.
- a coating layer made of a dielectric or a combination of a dielectric and a semiconductor on the exposed semiconductor end face.
- the coating layer is formed mainly for the purpose of increasing the light extraction efficiency from the semiconductor laser and for the purpose of protecting the end face.
- a coating layer with low reflectance (reflectance of 10% or less) for the oscillation wavelength is applied to the front end face, and high reflectance (for example, 80% or more) for the oscillation wavelength is applied. It is desirable to carry out asymmetric coating in which the coating layer is applied to the rear end face.
- O x, T i O x, S i O x, S i N x was one or selected from the group consisting of S i and Z n S Shi preferable to use two or more combinations Rere.
- a 1 O x , T i O x , S i O x, etc. are used as low-reflection coating layers, and A 1 O x / S i multilayer films, T i O x are used as high-reflection coating layers.
- a / S i O x multilayer film or the like is used. The desired reflectance can be achieved by adjusting the thickness of each film.
- the film thickness of A 1 O x , T i O x , S i O x, etc. to be used as a coating layer with low reflectance is around 4 ⁇ , where ⁇ is the real part of the refractive index at that wavelength ⁇ . It is common to adjust so that Also, in the case of a highly reflective multilayer film, it is general to adjust each material constituting the film so as to be in the vicinity of ⁇ / 4 ⁇ .
- the semiconductor laser shown in FIG. 2 was manufactured according to the following procedure.
- Si-doped n-type Ga As substrate carrier concentration 1 X 10 18 cn 3 (11 ) (the 350 m thick with a refractive index 3.5252 at 980 nm), as a first conductivity type buffer layer (12) Si-doped n-type GaAs layer with 0.5 / zm thickness and carrier concentration of 1 ⁇ 10 18 cm- 3 (refractive index 3.5252 at 980 nm); thickness as first conductivity type low refractive index layer (13) in Si-doped n-type a 1 0 carrier concentration 1 X 10 18 cm- 3. 5 G a. .
- a s layer (refractive index 3-2512 in 980 nm); as part of the first conductivity type secondary waveguide layer (14), the carrier concentration of 1 X 10 18 cm- 3 in the thickness 3.0 / im Si-doped n Type GaAs layers (refractive index 3.5252 at 980 nm) were epitaxially grown by MBE.
- n-type GaAs layer (refractive index 3.5252 at 980 nm) was grown.
- the surface grown by LPE was removed by mechano-chemical polishing, and the surface grown by MBE was removed.
- the sum of the thicknesses of the one-conductivity-type sub-waveguide layer and the first-conductivity-type sub-waveguide layer grown by the LPE method was set to be 29 ⁇ .
- the following layers were further epitaxially grown on this surface by the following method.
- the first conductivity type sub-waveguide layer As a part of the first conductivity type sub-waveguide layer, it also serves as a buffer for crystal growth, and has a thickness of 1.0 ⁇ and a carrier concentration of IX 10 18 cm- 3 Si-doped: ⁇ -type GaAs layer (at 980 nm)
- the refractive index of the first conductive type sub-waveguide layer was set to 30. ⁇ ⁇ .
- a Si-doped n-type A 1 with a thickness of 1.35 ⁇ and a carrier concentration of 1 X 10 18 cm- 3 as a first conductivity type cladding layer (15).
- Si-doped n-type GaAs having a thickness of 35 nm and a carrier concentration of 8 ⁇ 10 17 cm 3 as a second light guide layer (18);
- Zn-doped p-type Al with a carrier concentration of 1 ⁇ 10 18 cnT 3 was used as the second conductivity type upper cladding layer (22) by MOCVD. 35 G a.
- a 65 A s layer (refractive index at 980 nm: 3.3346) is grown so that the thickness of the buried portion (current injection region) is 2.5 ⁇ , and a second conductive layer for maintaining contact with the electrode is formed.
- As the type contact layer (23) a ⁇ -doped ⁇ -type GaAs layer (refractive index 3.5252 at 980 nm) with a carrier concentration of 6 ⁇ 10 18 cm ⁇ 3 was grown to a thickness of 3.5 ⁇ .
- the width W of the current injection region (the width of the upper cladding layer of the second conductivity type at the interface with the lower cladding layer of the second conductivity type) was 2.2 ⁇ m.
- the difference between the refractive indices of the current blocking layer (20) of the first conductivity type and the upper cladding layer (22) of the second conductivity type and the width were designed so that the waveguide mode was only the fundamental mode.
- TiZPt / Au was deposited as a p-side electrode, which is an epitaxy layer side electrode (202), and alloying was performed at 400 ° C for 5 minutes to complete the electrode structure.
- the thickness of the substrate is approximately 120 ⁇ m (excluding the extremely thin layers such as the first optical guide layer / active layer structure / second optical guide layer and the Z cap layer).
- the surface without the epitaxial layer of the first conductivity type substrate was polished so as to have a thickness of 80 ⁇ ).
- AuGeNiZAu was vapor-deposited as an n-side electrode serving as the substrate-side electrode (201), and alloying was performed at 400 ° C. for 5 minutes to complete a semiconductor wafer.
- the substrate was cleaved in the atmosphere into a laser bar with a resonance of 700 m, exposing the (110) plane.
- the A 1 Ox film was placed on the front end face at an oscillation wavelength of 980 nm.
- a 165 nm film was formed in a vacuum so that the reflectivity of the film became 2.5% to form a coating layer.
- the laser bar was once taken out of the vacuum layer.
- a 10-layer A10 layer with a thickness of 170 nm, an amorphous Si layer with a thickness of 60 nm, an A1 layer with a thickness of 170 nm, and a 4-layer coating layer of an amorphous Si layer with a thickness of 60 nm was formed, and a rear end face having a reflectance of 92% was formed.
- FIG. 3 shows the oscillation spectrum of the device when a current of 221.2 mA was injected, and very stable longitudinal mode oscillation was confirmed. This is due to the coupling between the laser waveguide and the sub-waveguide with a thickness of 30 m.
- the relationship between the intensity modulation period which is estimated to be approximately 10 nm in calculation and the gain spectrum of the laser, can be selectively set to one vertical position. It is considered that the mode was observed.
- the first conductive type low-refractive index layer (13) fabricated by MBE and the first conductive type sub-waveguide layer (14) fabricated by MBE and LPE methods are not embedded in the substrate.
- Example 1 was repeated except that the cap layer (21) was continuously grown by using the method and the first conductive type clad layer (15) and the second conductive type clad layer (22) were 1.5 ⁇ m. Similarly, a semiconductor laser was manufactured.
- FIG. 5 shows the oscillation spectrum of the device when a current of 195 mA was injected, and the effect of intensity modulation superimposed on the oscillation spectrum at approximately 2.9 nm intervals was confirmed. It consists of a laser waveguide and a waveguide. This is considered to be the result of the bonding of the substrate having a thickness of about 112 ⁇ that exhibits the wave function.
- FIG. 6 plots the current dependence of the wavelength of the longitudinal mode showing the maximum intensity in the oscillation spectrum in the above current range. The white triangle in the figure is the experimental result.
- the MBE Example 1 was repeated except that the cap layer (21) was continuously grown by using the method and the first conductivity type cladding layer (15) and the second conductivity type cladding layer (22) were set to 2.5 / Zm. Similarly, a semiconductor laser was manufactured.
- FIG. 8 is a plot of the current dependence of the wavelength of the longitudinal mode showing the maximum intensity in the oscillation spectrum in the above current range. The white circles in the figure are the experimental results.
- a semiconductor laser which can be manufactured by a simple method and has a stable oscillation wavelength with respect to changes in current / optical output / temperature and the like can be realized.
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- General Physics & Mathematics (AREA)
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- Semiconductor Lasers (AREA)
Abstract
Description
Claims
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AU2003262016A AU2003262016A1 (en) | 2002-09-20 | 2003-09-09 | Semiconductor laser |
JP2004537546A JP4345673B2 (ja) | 2002-09-20 | 2003-09-09 | 半導体レーザ |
US11/082,906 US7792170B2 (en) | 2002-09-20 | 2005-03-18 | Semiconductor laser |
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US11/082,906 Continuation US7792170B2 (en) | 2002-09-20 | 2005-03-18 | Semiconductor laser |
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JP (1) | JP4345673B2 (ja) |
CN (1) | CN100359772C (ja) |
AU (1) | AU2003262016A1 (ja) |
WO (1) | WO2004027950A1 (ja) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7957442B2 (en) | 2008-07-11 | 2011-06-07 | Sumitomo Electric Industries, Ltd. | Semiconductor optical device |
JP2011114214A (ja) * | 2009-11-27 | 2011-06-09 | Mitsubishi Electric Corp | 半導体レーザ装置 |
US8073029B2 (en) | 2008-01-30 | 2011-12-06 | Sumitomo Electric Industries, Ltd. | Semiconductor optical device |
Families Citing this family (3)
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CN104515740B (zh) * | 2013-09-17 | 2017-07-07 | 中央研究院 | 非标定型检测系统及其检测的方法 |
JP6496906B2 (ja) * | 2013-10-10 | 2019-04-10 | パナソニックIpマネジメント株式会社 | 半導体発光装置 |
CN109672088A (zh) * | 2018-12-29 | 2019-04-23 | 江西德瑞光电技术有限责任公司 | 一种半导体激光芯片制造方法 |
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JPS61156788A (ja) * | 1984-12-27 | 1986-07-16 | Sony Corp | 半導体レ−ザ− |
JPS63208290A (ja) * | 1987-02-25 | 1988-08-29 | Hitachi Ltd | 半導体レ−ザ装置 |
JPH07249795A (ja) * | 1994-03-09 | 1995-09-26 | Toshiba Corp | 半導体素子 |
JPH09232692A (ja) * | 1996-02-16 | 1997-09-05 | Lucent Technol Inc | 半導体レーザ装置 |
JP2001210910A (ja) * | 1999-11-17 | 2001-08-03 | Mitsubishi Electric Corp | 半導体レーザ |
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US5656832A (en) * | 1994-03-09 | 1997-08-12 | Kabushiki Kaisha Toshiba | Semiconductor heterojunction device with ALN buffer layer of 3nm-10nm average film thickness |
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2003
- 2003-09-09 JP JP2004537546A patent/JP4345673B2/ja not_active Expired - Fee Related
- 2003-09-09 AU AU2003262016A patent/AU2003262016A1/en not_active Abandoned
- 2003-09-09 CN CNB038253046A patent/CN100359772C/zh not_active Expired - Fee Related
- 2003-09-09 WO PCT/JP2003/011488 patent/WO2004027950A1/ja active Application Filing
Patent Citations (5)
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JPS61156788A (ja) * | 1984-12-27 | 1986-07-16 | Sony Corp | 半導体レ−ザ− |
JPS63208290A (ja) * | 1987-02-25 | 1988-08-29 | Hitachi Ltd | 半導体レ−ザ装置 |
JPH07249795A (ja) * | 1994-03-09 | 1995-09-26 | Toshiba Corp | 半導体素子 |
JPH09232692A (ja) * | 1996-02-16 | 1997-09-05 | Lucent Technol Inc | 半導体レーザ装置 |
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Title |
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HORIE, H ET AL: "Longitudinal-Mode Characteristics of Weakly Index-Guided Buried-Stripe Type 980-nm Laser Diodes with and without Substrate-Mode-Induced Phenomena.", IEE JOURNAL OF QUANTUM ELECTRONICS, vol. 36, no. 12, December 2000 (2000-12-01), pages 1454 - 1461, XP000977903 * |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8073029B2 (en) | 2008-01-30 | 2011-12-06 | Sumitomo Electric Industries, Ltd. | Semiconductor optical device |
US7957442B2 (en) | 2008-07-11 | 2011-06-07 | Sumitomo Electric Industries, Ltd. | Semiconductor optical device |
JP2011114214A (ja) * | 2009-11-27 | 2011-06-09 | Mitsubishi Electric Corp | 半導体レーザ装置 |
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Publication number | Publication date |
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AU2003262016A1 (en) | 2004-04-08 |
JPWO2004027950A1 (ja) | 2006-01-19 |
CN1701480A (zh) | 2005-11-23 |
CN100359772C (zh) | 2008-01-02 |
JP4345673B2 (ja) | 2009-10-14 |
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