JP2005311175A - Surface emitting laser and light transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface emitting laser wherein a current constriction structure can be formed with superior yield and sufficient controllability, stable laser property is installed, a planarize process is unnecessary, and mechanical strength is high. <P>SOLUTION: A lower semiconductor multilayer reflector (lower semiconductor DBR), a lower spacer layer, an activity layer, an upper spacer layer, a first upper semiconductor multilayer reflector (first upper semiconductr DBR), and a second upper multilayer reflector (second upper DBR), are arranged in order on a semiconductor substrate. In at least a part of layer of the first upper semiconductor multilayer reflector, a plurality of holes for high resistor region formation are arranged, oxidation is performed from a plurality of the holes, and high resistor regions are formed around the holes, so that a current constriction layer is formed which consists of a conductive region and the high resistor regions formed around the holes. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface emitting laser and an optical transmission system.

  A surface emitting laser (VCSEL) is a laser that forms a laser resonator in a direction perpendicular to a semiconductor substrate, injects current from a pair of electrodes, and emits oscillation light perpendicular to the substrate, and has the following advantages. .

  That is, since the active layer volume can be reduced, it can be driven with a low threshold current and low power consumption. Further, since the mode volume of the resonator is small, modulation of several tens of GHz is possible, which is suitable for high-speed transmission. Further, the spread angle of the emitted light is small, and the coupling to the optical fiber is easy. In addition, since the surface emitting laser does not require cleavage for production and has a small element area, it is easy to parallelize and form a two-dimensional high-density array.

  For this reason, the VCSEL is expected to be applied not only to an optical transmission light source such as a LAN but also to an optical transmission light source between boards, within a board, between LSI chips, and within a chip.

  The VCSEL has the following configuration. That is, a pair of high-reflectivity mirrors are provided on the substrate side and the surface side, an active layer is provided between these mirrors, and two upper and lower spacer layers are provided between the active layer and the two reflectors. Is provided.

  Furthermore, in order to reduce the threshold current, a current confinement structure for confining current in the vicinity of the active layer is provided. In this current confinement structure, in many cases, a method of forming a high resistance region in a region other than the vicinity of the light emitting portion is taken, and representative examples include a proton ion implantation method and a selective oxidation method.

  Here, the proton ion implantation method is, for example, a method of forming a high resistance region by implanting proton ions from the surface of the element constituent film as shown in Non-Patent Document 1.

  In addition, as shown in Non-Patent Document 2, for example, the selective oxidation method processes an upper part of an element configuration film including an Al (Ga) As film into a mesa shape by etching, and then forms an Al (Ga) As film. Is heat-treated in water vapor and oxidized from the mesa side wall to form a high resistance region.

  Of these two methods, the selective oxidation method, in addition to current confinement, has a large difference in refractive index between the conductive non-oxidized portion and the high-resistance oxidized region, so that light confinement is possible and single mode is achieved. In recent years, it has been adopted in many VCSELs for reasons such as easy oscillation.

However, in the selective oxidation method, in order to improve the heat dissipation of the heat generated in the light emitting part, to give mechanical strength, and to reduce the amount of carrier recombination on the side wall, the dimension of the mesa film surface direction is 30 × 30 μm ² or more is required, but the constriction size is about 5 × 5 μm ² , so the oxidation distance is 12 μm or more. In many cases, it is difficult to obtain this oxidation distance with good reproducibility. There's a problem.

  Further, since it is necessary to expose and oxidize at least the side surface of the selective oxidation layer close to the active layer, the height of the mesa becomes 3.5 to 9 μm, and the unevenness of the element surface becomes large. For this reason, it is necessary to perform a flattening process such as forming an upper electrode or forming a thick protective film at the time of mounting, and to set a process in which no load is applied to the mesa in order to prevent the mesa from being damaged.

  In order to solve the problem of the current confinement process by the selective oxidation method, for example, in Patent Document 1 and Patent Document 2, an element configuration film including an Al (Ga) As selective oxidation layer is formed and then covered from the surface. A method is shown in which a plurality of holes reaching the selective oxidation layer are formed by etching, water vapor is introduced through these holes, and heat treatment is performed to form a current confinement structure.

  According to this method, the current confinement structure can be formed with a short oxidation distance, and the element surface can be flattened.

  However, the depth of the Al (Ga) As selectively oxidized layer from the surface of the semiconductor element constituting film is in the position of 3 to 6.5 μm, and these holes need to reach this selectively oxidized layer, and the carrier In order to prevent non-radiative recombination, it is necessary not to reach the upper spacer layer. For this reason, the accuracy of the hole depth needs to be within ± 0.2 μm.

Normally, these holes are formed by a dry etching method, but even if an etching monitoring method such as emission spectroscopy is used, the controllability of the etching depth is about ± 5%. It is difficult to obtain this necessary accuracy.
B. Tell et al. , Appl. Phys. Lett. , 57 (1990) 1855 K. D. Choquette et al. IEEE Photonics Technology Letters. 7 (1995) 1237 Japanese Patent No. 3162333 JP-A-11-103129

  The present invention is capable of forming a current confinement structure with good yield and controllability, has a stable laser characteristic, does not require a flattening process, and has a high mechanical strength and a surface emitting laser (VCSEL) and an optical transmission system The purpose is to provide.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a lower semiconductor multilayer mirror (lower semiconductor DBR), a lower spacer layer, an active layer, an upper spacer layer, and a first upper semiconductor multilayer on a semiconductor substrate. A film reflecting mirror (first upper semiconductor DBR) and a second upper multilayer reflecting mirror (second upper DBR) are sequentially provided on at least a part of the first upper semiconductor multilayer reflecting mirror. Is provided with a plurality of holes for forming a high resistance region, and by oxidizing the plurality of holes for forming a high resistance region to form a high resistance region around the hole for forming a high resistance region, A current confinement layer comprising a high resistance region formed around the high resistance region forming hole is formed.

  According to a second aspect of the present invention, in the surface emitting laser according to the first aspect, the conductive region of the current confinement layer is an Al (Ga) As layer, and the high resistance region is the Al (Ga) layer. The As layer is composed of a layer oxidized by an oxidizing species supplied through the high resistance region forming hole.

  According to a third aspect of the present invention, in the surface emitting laser according to the first or second aspect of the present invention, at least part of the second upper multilayer mirror (second upper DBR) is a dielectric multilayer film. It is characterized by comprising.

  According to a fourth aspect of the present invention, in the surface emitting laser according to any one of the first to third aspects, at least the inner surface of the hole for forming the high resistance region is refracted lower than the element constituent film. It is characterized in that it is coated or filled with a rate of material.

  The invention according to claim 5 is the surface emitting laser according to any one of claims 1 to 4, wherein the active layer contains a GaInNAs-based material.

  According to a sixth aspect of the present invention, there is provided an optical transmission system in which the surface emitting laser according to any one of the first to fifth aspects is used as a light emitting device.

  According to the first aspect of the present invention, the upper DBR is divided into two, and the high resistance region forming hole is provided from the surface of the lower upper DBR (first upper semiconductor DBR). The hole for forming the high resistance region can be formed with high accuracy and reproducibility. By using such a hole for forming the high resistance region, the current confinement structure can be formed with good controllability, and stable laser characteristics can be obtained. It is possible to provide a surface emitting laser (VCSEL) that has a high mechanical strength and does not require a planarization step.

  More specifically, a surface emitting laser (VCSEL) having the following advantages can be obtained with a high yield. That is, in the surface emitting laser according to the first aspect of the present invention, the current confinement structure can be formed with a short oxidation distance, so that the yield in the current confinement structure forming process is improved. Further, it is not necessary to adopt a mesa structure that is inferior in heat dissipation, and the temperature of the element is hardly increased, so that stable laser characteristics can be obtained. In addition, since it is not necessary to have an uneven mesa structure, a flattening process is unnecessary and resistance to mechanical breakage is increased.

  According to a second aspect of the present invention, in the surface emitting laser according to the first aspect, the conductive region of the current confinement layer is made of an Al (Ga) As layer, and the high resistance region is made of the Al ( The Ga) As layer is composed of a layer oxidized by the oxidizing species supplied through the hole for forming the high resistance region, and the Al (Ga) As layer can be adjusted to a suitable resistance by changing the reaction conditions. Since it is used as a possible layer, the controllability of forming the current confinement structure can be further enhanced.

  According to the invention described in claim 3, since the dielectric DBR having high adaptability to the DBR is used as the second upper DBR, the function and effect of claim 1 can be obtained more easily.

  According to the invention of claim 4, since at least the inner surface of the high resistance portion forming hole is covered or filled with a refractive index material lower than that of the element constituent film, the light confinement becomes good and low. A surface emitting laser with a high threshold current, a high luminous efficiency, and a limited mode of output light can be obtained. Further, since defects on the inner surface of the hole for forming the high resistance portion are reduced, non-radiative recombination of carriers is reduced, whereby a surface emitting laser having a low threshold current and a high emission efficiency can be obtained.

  According to the invention described in claim 5, in the surface emitting laser according to any one of claims 1 to 4, the active layer includes a GaInNAs-based material, so that the yield is high and controllability is improved. A GaInNAs surface emitting laser capable of forming a current confinement structure can be obtained. Accordingly, it is possible to provide a surface emitting laser having higher performance laser characteristics, lower manufacturing cost, and high applicability to optical transmission.

Further, according to the invention described in claim 6, since the surface emitting laser according to any one of claims 1 to 5 is used as a light emitting device, the optical transmission system is further improved. A data transmission system with lower performance can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described.

(First form)
According to a first aspect of the present invention, a lower semiconductor multilayer reflector (lower semiconductor DBR), a lower spacer layer, an active layer, an upper spacer layer, a first upper semiconductor multilayer reflector (first mirror) are formed on a semiconductor substrate. An upper semiconductor DBR) and a second upper multilayer reflector (second upper DBR) are sequentially provided, and at least a part of the first upper semiconductor multilayer reflector includes a plurality of high resistance regions. Forming holes, and oxidizing the plurality of high resistance region forming holes to form high resistance regions around the high resistance region forming holes, thereby forming the conductive regions and the high resistance region forming holes. A surface emitting laser (VCSEL) characterized in that a current confinement layer comprising a high resistance region formed in the periphery is formed.

  Here, an upper electrode is provided in connection with at least a part of the first upper semiconductor multilayer film reflecting mirror, and at least a part of any layer between the lower spacer layer and the substrate is provided. A lower electrode is provided in connection with the region.

  In the surface emitting laser of the present invention, the conductive region of the current confinement layer is an Al (Ga) As layer, and the high resistance region is formed by the Al (Ga) As layer for forming the high resistance region. It consists of a layer oxidized by oxidizing species supplied through the holes.

  In the surface emitting laser, at least a part of the second upper multilayer reflector (second upper DBR) is made of a dielectric multilayer film.

  1 and 2 are views showing an example of the basic configuration of the surface emitting laser of the present invention described above. 1 is a plan view (a cross-sectional view of a high-resistance layer described later), and FIG. 2 is a cross-sectional view taken along the line AA of FIG.

  Referring to FIGS. 1 and 2, on a semiconductor substrate such as GaAs, InP, GaP, GaNAs, Si, Ge, etc., a lower semiconductor multilayer reflector (lower semiconductor DBR), a lower spacer layer, an active layer, an upper spacer layer, A first upper semiconductor multilayer reflector (first upper semiconductor DBR), an upper electrode, and a second upper multilayer reflector (second upper DBR) are sequentially formed.

  The lower semiconductor DBR is composed of a multilayer film such as AlAs / GaAs, AlGaAs / GaAs, GaInP / GaAs, AlGaN / GaN, GaInAsP / InP, AlGaInAs / InP as a combination with the substrate (lower semiconductor DBR / substrate). . In these substrates and the lower semiconductor DBR, the portion that becomes the path of the drive current is doped with impurities to have conductivity.

  The active layer is selected according to the oscillation wavelength, and combinations with the substrate (active layer / substrate) include GaInAsP / InP [1.3 μm band, 1.55 μm band], GaInNAs / GaAs [1.3 μm band, 1 .55 μm band], GaInAs / GaAs [0.98 μm band], GaAlAs / GaAs [0.85 μm band], AlGaInP / GaAs [0.65 μm band], and the like.

  Further, the upper spacer layer and the lower spacer layer have a function of adjusting the resonator length, transporting carriers to the active layer, and being transparent to the emitted light. Specifically, the upper spacer layer and the lower spacer layer are selected from GaAs, InP, GaInAsP, GaAlAs, AlGaInP, GaInP, and the like depending on the active layer material.

  The first upper semiconductor multilayer mirror (first upper semiconductor DBR) is composed of a multilayer film such as AlAs / GaAs, AlGaAs / GaAs, GaInP / GaAs, AlGaN / GaN, GaInAsP / InP, and AlGaInAs / InP. Then, the impurity is doped to have a conductivity opposite to that of the lower semiconductor DBR. Specifically, the number of layers of the first upper semiconductor DBR is 10 pairs or less, and the controllability of the etching depth required in an etching process for forming a high resistance region forming hole described later is ± 5. It is preferable because it is within a percentage.

In addition, the high resistance layer made of a material that can be increased in resistance by processing through a hole for forming a high resistance region, which will be described later, is made of Al _x Ga _1-x As (0 <x ≦ 1) [below Al (Ga) As] is desirable because the difference in refractive index between the oxidized region and the non-oxidized region is large and the effect of confining light is great. If the value of x is 0.95 or more, it is desirable because the oxidation rate becomes so large that it can be controlled.

  The high resistance layer may be provided in the upper spacer layer, but is preferably included in the first upper semiconductor DBR as a low refractive index layer.

  As a growth method of the semiconductor film (lower semiconductor DBR, lower spacer layer, active layer, upper spacer layer, first upper semiconductor multilayer mirror (first upper semiconductor DBR)), MOCVD (metal organic chemical deposition) is used. ), MOMBE method (metalorganic molecular epitaxy), CBE method (chemical beam epitaxy), or the like can be used.

  Then, the high resistance region forming hole can be formed by etching from the surface of the first upper semiconductor DBR.

  The cross-sectional shape of the high resistance region forming hole may be a closed shape, and may take any shape such as a circle, a rectangle, a polygon, and an ellipse. Further, the number, size, arrangement and the like of the high resistance region forming holes are not limited.

  Further, it is desirable that the bottom of the hole for forming the high resistance region is provided at a position that penetrates the high resistance layer and does not reach the upper spacer layer.

  As an etching method for forming the hole for forming the high resistance region, dry etching or wet etching can be used. However, dry etching is preferable because the etching rate in the direction perpendicular to the side etching rate is large. Further, as a dry etching method, a method using a high-density plasma source such as an ICP (Inductively Coupled Plasma) etching method or an ECR (Electron Cyclotron Resonance) etching method which can increase etching anisotropy is preferable.

Using this high resistance region forming hole, a current confinement structure can be formed as follows. That is, H ₂ O, O ₂ , H element and O element are introduced into the semiconductor in the vicinity of the active layer through this high resistance region forming hole by gas flow, ion implantation, thermal diffusion, etc. to form a high resistance region. The current confinement structure can be formed by changing the high-resistance layer around the hole to a high-resistance region and leaving only the vicinity of the light-emitting region of the active layer conductive. In particular, when an Al (Ga) As layer is used for the high resistance layer, a current confinement structure can be formed by introducing water vapor or O ₂ gas and performing heat treatment at about 400 ° C.

Further, the upper electrode is formed of a metal mainly composed of Au or the like, and when the light output is in the direction of the element surface, the upper electrode is formed by a lift-off method or the like in a shape having no electrode in the light output portion. In order to form a current confinement structure when forming the upper electrode, it is desirable that the upper electrode material does not enter the bottom of the high resistance region forming hole. This configuration can be realized by an oblique deposition method of an electrode material or a method of forming an electrode film after covering the entrance of the high resistance region forming hole with SiO ₂ , SiN, an organic material, or the like.

  The second upper DBR is formed on the sample surface. The second upper DBR may be a semiconductor DBR, but since there are many high resistance region forming holes and electrodes on the surface of the sample at the time of forming the second upper DBR, Epitaxial growth is difficult. Accordingly, the second upper DBR is easy to manufacture and can have a large difference in refractive index (that is, a high reflectance can be obtained with a small number of layers). DBR) is preferred.

Examples of the dielectric DBR include multilayer films such as ZrO ₂ / SiO ₂ , MgO / SiO ₂ , MgO / Si, and Al ₂ O ₃ / MgF _{2. Since} the dielectric DBR is an insulator, the pad of the upper electrode is used. It can be formed not only on the entire surface of the element but also on the entire surface of the array.

  As a growth method of the dielectric film and the electrode film, for example, an electron beam vapor deposition method, a sputtering method, a resistance heating method, or a CVD method (chemical vapor deposition) can be used.

  The isolation region of the element can be formed by providing a narrow trench structure or ion implantation of protons or oxygen ions.

FIG. 3 is a diagram showing a first configuration example of the surface emitting laser according to the present invention. Referring to FIG. 3, the surface emitting laser of the first configuration example includes a lower n-type semiconductor DBR, a lower non-doped spacer layer, an active layer, an upper non-doped spacer layer, and a first upper p-type semiconductor DBR on an n-type substrate. Are sequentially epitaxially grown, and a p-type Al (Ga) As high resistance layer is provided in the third pair of low refractive index layers from the bottom of the first upper p-type semiconductor DBR. Then, a number of holes for forming a high resistance region are formed around the resonator region of the first upper p-type semiconductor DBR by ECR etching using the SiO ₂ film as a mask. Note that the bottoms of the holes are in two pairs of lower layers of the first upper p-type semiconductor DBR. Then, a current confinement structure can be formed by introducing molecules or elements that increase the resistance into the high resistance region forming hole. Then, after removing the SiO ₂ film, an upper p-ohmic electrode is formed on the first upper p-type semiconductor DBR. This upper p-ohmic electrode is open in the light output region.

A second upper dielectric (ZrO ₂ / SiO ₂ ) DBR is formed on the surface excluding the electrode pad portion that is the wiring connection portion of the upper p-ohmic electrode.

  An n-ohmic electrode is formed on the back surface of the substrate.

  In the surface emitting laser having such a configuration, positive and negative carriers can be injected from the p-side electrode and the n-side electrode, respectively, to emit light in the active layer, and laser oscillation can be performed in a direction perpendicular to the substrate. The light output is taken out from the element surface side.

  The surface emitting laser according to the present invention described above has a structure in which the upper DBR is divided into two, and a hole for forming a high resistance region is provided from the surface of the lower upper DBR (first upper DBR). The hole for forming the high resistance region can be formed with high reproducibility, and the current confinement structure can be formed with good controllability by using such a hole for forming the high resistance region, and has stable laser characteristics. A surface-emitting laser (VCSEL) with high mechanical strength that does not require a planarization step can be provided.

  More specifically, a surface emitting laser (VCSEL) having the following advantages can be obtained with a high yield. That is, in the surface emitting laser according to the present invention, since the current confinement structure can be formed with a short oxidation distance, the yield in the current confinement structure forming process is improved. Further, it is not necessary to adopt a mesa structure that is inferior in heat dissipation, and the temperature of the element is hardly increased, so that stable laser characteristics can be obtained. In addition, since it is not necessary to have an uneven mesa structure, a flattening process is unnecessary and resistance to mechanical breakage is increased.

  In addition, since an Al (Ga) As layer whose oxidation rate can be appropriately adjusted by changing the reaction conditions is used as the high resistance layer, the controllability of the current confinement structure formation can be further enhanced.

  Further, by using a dielectric DBR having high adaptability to the DBR as the second upper DBR, the above-described operational effects of the present invention can be obtained more easily.

  In the surface emitting laser of the present invention described above, as a second configuration example, as shown in FIG. 4, at least the inner surface of the high resistance region forming hole is covered with a material having a refractive index lower than that of the element constituent film. Or the structure filled can be taken.

  Here, the high resistance region forming hole is often provided so that at least a part thereof has a periodic structure.

In addition, an organic polymer such as polyimide, an inorganic material such as SiO ₂ , SiON, and Al ₂ O ₃ can be used for the coating or filling, and these include a coating method, a vapor deposition method, a sputtering method, a CVD method, and the like. Formed with.

  For surface emitting lasers, optical confinement in the resonator is an important issue in order to increase the output efficiency by lowering the threshold current and to limit the resonance mode.

  In the second configuration example, the inner surface of the hole for forming the high resistance region is covered or filled with a material having a low refractive index instead of a metal, so that the loss of light is low.

  The “low-loss periodic dielectric medium” is a photonic crystal structure (written by John D. Joannnopoulos et al., Translated by Fujii et al., “Photonic Crystal” published by Corona). Therefore, in the second configuration example, a two-dimensional photonic crystal structure is often automatically formed.

  By taking this two-dimensional photonic crystal structure, the propagation of light in the horizontal direction is reduced by confining the light in the horizontal direction by light diffraction and by effectively reducing the refractive index at the periphery of the light emitting region. Sometimes it works. The former is a case where a photonic band gap is used, and the latter is a case where the photonic band gap is not used.

  That is, the second configuration example includes the case where the high resistance region forming hole has a photonic crystal structure.

  As described above, in the second configuration example, at least the inner surface of the high resistance portion forming hole is covered or filled with the refractive index material lower than that of the element constituent film, so that the light confinement is improved and the low threshold is set. A surface emitting laser with high current efficiency, high luminous efficiency, and limited output light mode can be obtained. In addition, since defects on the inner surface of the hole for forming the high resistance portion are reduced, non-radiative recombination of carriers is reduced, whereby a surface emitting laser having a low threshold current and a high emission efficiency can be obtained.

  The surface-emitting laser of the second configuration example can also inject positive carriers and negative carriers from the p-side electrode and the n-side electrode to emit light in the active layer and cause laser oscillation in a direction perpendicular to the substrate. it can.

  In the surface emitting laser of the present invention (including the first and second configuration examples) described above, a GaInNAs-based material can be included in the active layer as in the example shown in FIG.

  The GaInNAs-based material is composed of a III-V group mixed crystal semiconductor containing N and As, specifically, composed of GaNAs, GaInNAs, GaInAsSb, GaInNP, GaNP, GaNAsSb, GaInNAsSb, InNAs, InNPAs, and the like. .

  A long-wavelength surface emitting laser with an oscillation wavelength of about 1.1 to 1.6 μm propagates the oscillation light through the silica-based fiber with little loss, and transmits through the Si substrate with little absorption. Since it has features, it is particularly applicable as a light transmission light source between chips, between chips, between boards, within boards, and within LANs.

  Conventionally, this long wavelength band VCSEL has been attempted with a GaInAsP active layer formed on an InP substrate that has a proven track record as an edge emitting laser. However, the GaInAsP-based VCSEL on the InP substrate has low temperature characteristics in the material structure around the active layer that can be taken, as in the case of the edge emitting laser. In addition, for the semiconductor DBR on the InP substrate, GaInAsP / InP having a small refractive index difference must be selected, so that it is difficult to increase the reflectance. For this reason, a cooling device is required, and there are many other problems in practical use.

  On the other hand, a GaInNAs long wavelength band VCSEL fabricated on a GaAs substrate has high temperature characteristics, and can use a DBR of AlGaAs / GaAs or AlAs / GaAs that can increase the reflectivity because the difference in refractive index can be increased. Since the oscillation wavelength is long, it is advantageous to use AlAs / GaAs DBR which is a combination of materials having particularly high thermal conductivity. In this regard, GaInAs and GaAsSb have the same effect. Furthermore, it oscillates at room temperature and has a small threshold current.

  Because of these advantages, GaInNAs long wavelength band VCSELs have been actively researched and developed in recent years.

  Thus, according to the configuration of the present invention, it is possible to obtain a GaInNAs surface emitting laser capable of forming a current confinement structure with good yield and good controllability. Accordingly, it is possible to provide a surface emitting laser having higher performance laser characteristics, lower manufacturing cost, and high applicability to optical transmission.

(Second form)
According to a second aspect of the present invention, there is provided an optical transmission system in which the above-described surface emitting laser according to the present invention is used as a light emitting device.

  5 and 6 are diagrams showing a configuration example of the optical transmission system of the present invention.

  The optical transmission system in the example of FIG. 5 is a parallel optical transmission system between boards equipped with the surface emitting laser (VCSEL) of the present invention, and is configured to simultaneously transmit signals from the VCSEL using a plurality of fibers. Has been.

  The optical transmission system in the example of FIG. 6 is a parallel space optical transmission system between chips between boards equipped with the GaInNAs surface emitting laser (VCSEL) of the present invention. In this example, the signal from the VCSEL Is transmitted through the Si substrate and transmitted simultaneously.

  As described above, in the second mode, since the surface-emitting laser of the first mode described above is used as a light-emitting device, a higher-performance and lower-cost data transmission system is provided. Can be provided.

  7 and 8 show the surface emitting laser of Example 1. FIG. 7 is a plan view (a cross-sectional view taken on the surface of an AlAs film to be described later), and FIG. 8 is a cross-sectional view taken along the line AA in FIG.

  The surface emitting laser of Example 1 is manufactured as follows.

  That is, first, by MOCVD, on a n-GaAs single crystal (100) substrate, a lower semiconductor DBR composed of 35.5 pairs of n-AlGaAs / n-GaAs, a lower GaAs spacer layer, a GaInNAs / GaAs TQW active layer, A laminated film of a first upper semiconductor DBR composed of a GaAs spacer layer and 6 pairs of p-AlGaAs / p-GaAs is produced.

  Here, the second pair of low refractive index layers from the bottom of the first upper semiconductor DBR is a p-AlAs high resistance layer.

  Next, a resist is applied to the surface of the laminated film. Corresponding to the position where the resonator is provided in the basic pattern in which the unit shape in which the resist is removed in a circular shape having a diameter of 2.5 μm and four apexes of a square having a side length of 5 μm from this coating film is cyclically repeated. At the place, a resist pattern in which one circular resist is not removed is formed.

Next, a high resistance region forming hole is formed by an ICP etching method in which Cl ₂ gas is introduced. The depth of the high resistance region forming hole is set so that the bottom surface of the hole reaches the first pair of the lower layer of the first upper semiconductor DBR.

After removing the resist, water vapor is introduced from the end face of the p-AlAs high resistance layer exposed on the inner wall of the hole for forming the high resistance region, and the AlAs layer is oxidized in the in-plane direction to form an AlxOy high resistance layer. AlxOy high resistance layers grown from adjacent high resistance region forming holes are connected to form a high resistance region. At this time, the current confinement structure is formed by controlling the oxidation time so that the AlAs film having a cross section of about 16 μm ² remains unoxidized at the position corresponding to the position where the resonator is provided.

  Next, a p-electrode film is formed. Next, the p-electrode film in the light output region is removed by a lift-off method, and at the same time, an upper p-electrode pattern (p-upper electrode) is formed.

Next, a second upper dielectric DBR composed of a ZrO ₂ / SiO ₂ 6 pair is formed by EB vapor deposition. Next, the wiring connection pad of the upper p-electrode pattern is exposed by a lift-off method.

  Finally, an n-electrode is formed on the back surface of the substrate to produce a 1.3 μm band surface emitting laser.

  In the surface emitting laser of Example 1 of FIGS. 7 and 8, when positive carriers and negative carriers are injected from the p-side electrode and the n-side electrode, respectively, laser light is output perpendicularly to the substrate from the element surface.

  In the surface emitting laser of Example 1, the required depth of the hole for forming the high resistance region is shallow, so that the hole can be formed with better controllability. Therefore, it is possible to provide a surface emitting laser having a stable characteristic because it has a current confinement structure with high yield, high dimensional uniformity, good flatness, high mechanical strength, and good heat dissipation. In addition, a GaInNAs surface emitting laser having high-performance laser characteristics, lower manufacturing cost, and high applicability to optical transmission can be obtained.

  9 and 10 are diagrams showing a surface emitting laser according to Example 2. FIG. FIG. 9 is a plan view (a cross-sectional view taken along an Al (Ga) As film surface described later), and FIG. 10 is a cross-sectional view taken along the line AA in FIG.

Referring to FIGS. 9 and 10, the surface emitting laser of Example 2 is the 1.3 μm band VCSEL with the same configuration and process as in Example 1 except that the high resistance region forming hole is covered with a SiO ₂ film. Is made.

The process of covering with this SiO ₂ film will be described.

First, after a current confinement structure is formed by oxidation, a SiO ₂ film is formed on the surface of the sample including the inner surface of the high resistance region forming hole by plasma CVD.

After covering the high resistance region forming hole with a resist, the SiO ₂ film on the surface of the first upper semiconductor DBR is removed by BHF. Next, this resist is removed. Next, after the step of forming the p-electrode film, the same process as in Example 1 is performed.

  In the surface emitting laser of Example 2 in FIGS. 9 and 10, when positive carriers and negative carriers are injected from the p-side electrode and the n-side electrode, respectively, laser light is output perpendicularly to the substrate from the element surface. The threshold current density is smaller than that in the first embodiment.

  Thus, in the surface emitting laser of Example 2, the following effect is further added to the function and effect of Example 1. That is, in the surface emitting laser of Example 2, since the inner surface of the high resistance portion forming hole is coated with a low refractive index material, light confinement is improved, current leakage is reduced, and a low threshold current is obtained. A surface emitting laser with a single mode output light having high density and high luminous efficiency can be obtained.

  FIG. 11 is a cross-sectional view of the surface emitting laser according to the third embodiment. The plan view of the surface emitting laser of Example 3 (transverse sectional view of the Al (Ga) As film surface described later) is the same as FIG. 9, and FIG. 11 is taken along the line AA in FIG. 10 is a cross-sectional view of Example 3. FIG.

  The surface emitting laser of Example 3 is manufactured as follows. That is, first, by MOCVD, on a n-GaAs single crystal (100) substrate, a lower semiconductor DBR composed of 27.5 pairs of n-AlGaAs / n-GaAs, a lower GaAs spacer layer, a GaInAs / GaAs TQW active layer, A laminated film of a first upper semiconductor DBR composed of a GaAs spacer layer and 10 pairs of p-AlGaAs / p-GaAs is produced.

Here, the third pair of low refractive index layers from the bottom of the first upper semiconductor DBR is a p-Al _0.95 Ga _0.05 As high resistance layer.

  Next, a resist is applied to the surface of the laminated film. Corresponding to the position where the resonator is provided in the basic pattern in which the unit shape in which the resist is removed in a circular shape having a diameter of 2.5 μm and four apexes of a square having a side length of 5 μm from this coating film is cyclically repeated. At the place, a resist pattern in which one circular resist is not removed is formed.

Next, a high resistance region forming hole is formed by an ECR etching method in which Cl ₂ gas is introduced. The depth of the hole for forming the high resistance region is set so that the bottom surface of the hole is in one to two pairs of the lower layer of the first upper semiconductor DBR.

After removing the resist, water vapor is introduced from the end face of the p-Al _0.95 Ga _0.05 As high resistance layer exposed on the inner wall of the hole for forming the high resistance region, and the AlGaAs layer is oxidized in the in-plane direction to form AlxOy. A high resistance layer is formed. The oxide high resistance layer grown from the adjacent hole for forming the high resistance region is connected to form a high resistance region. At this time, the current confinement structure is formed by controlling the oxidation time so that the AlGaAs layer having a cross section of about 16 μm ² remains unoxidized at the position corresponding to the position where the resonator is provided.

Next, a SiO ₂ film is formed on the surface of the sample including the inner surface of the high resistance region forming hole by plasma CVD.

After removing the SiO ₂ film in a part of the surface of the first upper semiconductor DBR, a p-electrode film is formed. Next, an upper p-electrode pattern (p-upper electrode) is formed.

Next, a second dielectric DBR composed of 10 pairs of MgO / SiO ₂ is formed by EB vapor deposition. Next, the wiring connection pad of the upper p-electrode pattern is exposed by a lift-off method.

  Lastly, a 0.98 μm band surface emitting laser can be manufactured by forming an n-electrode having a light exit portion on the back surface of the substrate using a metal mask.

  In the surface emitting laser of Example 3 in FIG. 11, when positive carriers and negative carriers are injected from the p-side electrode and the n-side electrode, respectively, laser light is output perpendicularly to the substrate from the back surface of the substrate.

  In the surface emitting laser of Example 3, the required depth of the high resistance region forming hole is shallow, so that the hole can be formed with better controllability. Therefore, it is possible to provide a surface emitting laser having a stable characteristic because it has a current confinement structure with high yield, high dimensional uniformity, good flatness, high mechanical strength, and good heat dissipation. In addition, since the inner surface of the hole for forming the high resistance portion is coated with a low refractive index material, light confinement is improved, current leakage is reduced, a low threshold current density, a high luminous efficiency, and a single light emitting diode are provided. A surface emitting laser with one-mode output light is obtained.

  12 and 13 are diagrams showing a surface emitting laser according to Example 4. FIG. 12 is a plan view (transverse cross-sectional view at the upper DBR film surface), and FIG. 13 is a cross-sectional view taken along line BB in FIG.

  12 and 13, the surface emitting laser of Example 4 has the same configuration as that of Example 2 except that the pattern of the holes for forming the high resistance region is a triangular lattice pattern. Fabricated as a 1.3 μm band VCSEL in the process.

  The process of forming the triangular lattice pattern is as follows. That is, on the surface of the laminated film, the resonator is formed in a pattern in which a unit shape in which a circle having a diameter of 2.5 μm is removed from three apexes of a regular triangle having a side length of 5 μm from the resist coating film is periodically repeated. A resist pattern in which one circular resist is not removed is formed at a location corresponding to the position to be provided.

The surface emitting laser of the fourth embodiment can also obtain the same effects as the second embodiment.

It is a figure which shows the basic structural example of the surface emitting laser of this invention. It is a figure which shows the basic structural example of the surface emitting laser of this invention. It is a figure which shows the 1st structural example of the surface emitting laser of this invention. It is a figure which shows the 2nd structural example of the surface emitting laser of this invention. It is a figure which shows the structural example of the optical transmission system of this invention. It is a figure which shows the structural example of the optical transmission system of this invention. 1 is a diagram showing a surface emitting laser of Example 1. FIG. 1 is a diagram showing a surface emitting laser of Example 1. FIG. It is a figure which shows the surface emitting laser of Example 2. FIG. It is a figure which shows the surface emitting laser of Example 2. FIG. 6 is a sectional view of a surface emitting laser according to Example 3. FIG. 6 is a view showing a surface emitting laser according to Example 4. FIG. 6 is a view showing a surface emitting laser according to Example 4. FIG.

Claims (6)

On a semiconductor substrate, a lower semiconductor multilayer reflector (lower semiconductor DBR), a lower spacer layer, an active layer, an upper spacer layer, a first upper semiconductor multilayer reflector (first upper semiconductor DBR), and a second upper portion A multilayer reflector (second upper DBR) is sequentially provided, and at least a part of the first upper semiconductor multilayer reflector is provided with a plurality of holes for forming a high resistance region. By oxidizing the high resistance region forming hole to form a high resistance region around the high resistance region forming hole, a conductive region and a high resistance region formed around the high resistance region forming hole, A surface-emitting laser characterized in that a current confinement layer made of is formed. 2. The surface emitting laser according to claim 1, wherein the conductive region of the current confinement layer is an Al (Ga) As layer, and the high resistance region is formed by the Al (Ga) As layer being the hole for forming the high resistance region. A surface emitting laser comprising a layer oxidized by an oxidizing species supplied through the surface emitting laser. 3. The surface emitting laser according to claim 1, wherein at least a part of the second upper multilayer reflector (second upper DBR) is made of a dielectric multilayer film. Light emitting laser. 4. The surface emitting laser according to claim 1, wherein at least an inner surface of the high resistance region forming hole is coated or filled with a material having a refractive index lower than that of the element constituent film. A surface emitting laser characterized by the above. 5. The surface emitting laser according to claim 1, wherein the active layer includes a GaInNAs-based material. 6. 6. An optical transmission system, wherein the surface emitting laser according to claim 1 is used as a light emitting device.

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