JP3800856B2 - Surface emitting laser and surface emitting laser array - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface-emitting laser and a surface-emitting laser array, and more particularly to an oxidation-type surface-emitting laser and a surface-emitting laser array that are resistant to stress and highly reliable.
[0002]
[Prior art]
Vertical cavity surface emitting laser (VCSEL) has many advantages such as low manufacturing cost, high yield, and easy two-dimensional array compared to conventional edge-emitting lasers. Due to these advantages, their use has been studied in many applications. For example, Kenichi Iga, Fumio Koyama and Susumu Kinoshita, "Surface Emitting Semiconductor Lasers", IEEE Journal of Quantum Elecronics, 1988, 24, pp.1845-1855, explains the structure, laser characteristics, applications, etc. of VCSEL In addition, the laser characteristics have been greatly improved so far, and it has been put into practical use in fields such as optical communication.
[0003]
In particular, AlAs oxidized VCSEL ("Native-oxide defined ring contact for low threshold vertical-cavity lasers", reported by DLHufaker et al., Appl. Phys. Lett., Vol. 65, No. 1, pp. 97-99, '94) has excellent characteristics such as low threshold current, high efficiency, and fast response speed, and is actively researched as a promising technology.
[0004]
However, as reported by KDChoquette et al. ("Selective Oxidation of buried AlGaAs Versus AlAs layers", Appl. Phys. Lett., Vol.69, No.10, pp.1385-1387). , '96), the volume of the AlAs layer that is oxidized is contracted due to oxidation, and the device is cracked and destroyed in the process after oxidation, resulting in a decrease in manufacturing yield and a short device life. Have problems such as.
[0005]
As shown in a cross-sectional view of a general oxidized VCSEL, the element is formed in a post shape and is isolated. Therefore, in the plane where the AlAs oxide layer 90 is present, the semiconductor layers are connected by the crystal structure only in the central non-oxidized portion 91 having a diameter of several μm. The portions connected by this crystal structure are free from defects and voids and are resistant to stress, but conversely, the oxide layer 90 has defects and voids and cracks are caused by the stress, resulting in element destruction.
[0006]
As one of the countermeasures for preventing such element destruction, there is a method of reducing volume shrinkage by changing the layer to be oxidized from AlAs to AlGaAs containing several percent of GaAs as described in the above report. In this case, the volume shrinkage is reduced from 12% or more to 6.7%, and defects and voids existing in the oxide layer are remarkably reduced. As a result, device destruction during the manufacturing process is eliminated, and device life is extended. It has been reported.
[0007]
[Problems to be solved by the invention]
However, the above preventive measures have the following problems.
First, the problem of the method for reducing the volume shrinkage by changing the layer to be oxidized from AlAs to AlGaAs containing several percent of GaAs will be described. The characteristics of the oxidized VCSEL greatly depend on the diameter of the current injection region which is a non-oxidized region. Therefore, it is important to control the oxidation distance of the AlAs or AlGaAs layer. However, the oxidation rate is greatly influenced by the composition of AlGaAs. For example, in AlGaAs containing 2% AlAs and GaAs, the oxidation rate differs by 10 times or more. On the other hand, during epitaxial growth, it is very difficult to control the GaAs concentration of AlGaAs within the substrate plane and between the substrates to such an extent that the oxidation rate is not affected, which is not suitable for commercial production.
As described above, the conventional reinforced oxide surface emitting laser has several problems, and no practical one has been obtained yet.
[0008]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an oxide surface emitting laser array that has a simple manufacturing process, is resistant to stress, and has high reliability.
[0009]
[Means for Solving the Problems]
The present inventors have intensively studied and, as a result, have to Heading that the above problems can be solved by the following means.
[0010]
The surface-emitting laser array of the present invention is provided on a substrate between an active region composed of an active layer and a pair of spacer layers that sandwich the active layer, a pair of reflective layers that sandwich the active region, and the pair of reflective layers. A laminated portion formed by laminating an AlAs selective oxidation layer whose peripheral portion is oxidized while leaving a part of the non-oxidized region is formed in a mesa shape, and the non-oxidized region is selectively oxidized in the same AlAs in the same mesa. A plurality of layers are formed in the layer, and two or more of the non-oxidized regions are current injection regions.
[0011]
In the surface emitting laser array of the present invention, one AlAs selective oxidation layer of one mesa is provided with two or more non-oxidized regions connected to each other by a crystal structure from the substrate. The structure is more resistant to stress than when a non-oxidized region is provided and one oxidized VCSEL is formed.
[0012]
Also performs current injection into all or some of the plurality of the non-oxidized region of said surface emitting laser, by forming a plurality of light emitting areas, it is possible to obtain a surface-emitting laser array structure strong to stress.
[0013]
Therefore, according to the present invention, it is possible to provide an oxidized VCSEL array that has a simple manufacturing process, is resistant to stress, and has high reliability. In addition, structural anisotropy can be imparted in the direction in which the mesa extends with respect to the light emitting region, thereby generating anisotropy of stress and a secondary effect that polarization control of the laser beam can be expected. it can.
Further, since the VCSEL element, the part for forming the electrode pad, and the part for connecting the VCSEL element and the electrode pad can be formed at the same height, that is, there is a step between the VCSEL element and the electrode pad. Therefore, the electrode can be easily formed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described based on embodiments.
[0015]
(First embodiment)
The surface-emitting laser array according to the first embodiment of the present invention has a structure in which two oxidized VCSELs are formed using one mesa 26 as shown in FIG. In this structure, as shown in FIGS. 2A to 2C, two non-oxidized regions 20 a are provided in the AlAs selective oxide layer 20 in one mesa 26. Hereinafter, the structure of the surface emitting laser array according to the first embodiment of the present invention will be described in accordance with a manufacturing method.
[0016]
First, as shown in FIG. 3A, the film thickness of AlAs and GaAs on the n-type GaAs substrate 10 becomes 1/4 of the wavelength in the medium by metal organic chemical vapor deposition (MOCVD). The lower n-type DBR (Distributed Bragg Reflector) layer 12, the undoped lower Al _0.22 Ga _0.78 As spacer layer 14 and the undoped quantum well active layer having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ stacked alternately for 30 periods as described above 16 (consisting of 3 layers of 80 nm InGaAs quantum well layers and 4 layers of 150 nm GaAs barrier layers) and the undoped upper Al _0.22 Ga _0.78 As spacer layer 18 is the wavelength in the medium. active layer region 30 made, thereon, p-type AlAs layer 20 in which the concentration 1 × 10 ¹⁸ cm ^-3 thickness carrier is ¼ of the wavelength in the medium, Al _0.9 Ga _0.1 as and GaAs thereon The upper p-type DBR layer 22 in which the carrier concentration of 1 × 10 ¹⁸ cm ^-3 total thickness was 22 cycles alternately stacked so that 1/4 of the respective thickness-medium wavelength of about 2 [mu] m, on which A p-type GaAs contact layer 24 having a film thickness λ with a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ is sequentially stacked.
[0017]
The source gas is trimethylgallium, trimethylaluminum, trimethylindium, arsine, the dopant material is cyclopentadinium magnesium for p-type and silane for n-type, the substrate temperature during growth is 750 ° C., and vacuum is used. Without breaking, the source gas was changed sequentially, and the film was formed continuously.
[0018]
Next, as shown in FIG. 3B, the laminated film is etched partway through the lower n-type DBR layer 12 to form a mesa 26 to expose the side surface of the AlAs layer 20. In order to process the mesa shape, a resist mask R was formed on the crystal growth layer by photolithography, and reactive ion etching using carbon tetrachloride as an etching gas was used.
[0019]
Thereafter, the resist mask R is removed, and as shown in FIG. 3C, only the AlAs layer 20 is oxidized from the side by water vapor in a furnace at about 400 ° C. to increase the resistance, and the oxidized region 32 and the non-oxidized region 20a. The diameter of the non-oxidized region is about 3 μm. This non-oxidized region 20a becomes a current injection region. In FIG. 2A, the boundary line between the oxidized region 32 and the non-oxidized region 20a of the AlAs selective oxide layer 20 is indicated by a broken line.
[0020]
Thereafter, as shown in FIGS. 3D and 3E, a SiN insulating film 34 is deposited except for the upper surface of the mesa 26, and the resist mask R is used to remove the exit port 40 and p of Ti / Au. The side electrode 36 is formed. Au / Ge is vapor-deposited as an n-side electrode 38 on the back surface of the substrate 10. In this way, the surface emitting laser array shown in FIG.
[0021]
The surface emitting laser array of this embodiment has two portions (non-oxidized regions 20a) connected to the substrate 10 by a crystal structure, and a general VCSEL in which one oxidized VCSEL is formed for each mesa. This has higher strength than stress.
[0022]
In this embodiment, in order to functionally separate the elements, the p-side electrode is separated, and protons are implanted between the VCSELs to increase the resistance.
[0023]
In the present embodiment, the mesa 26 is formed so that the non-oxidized region 20a is circular. However, as shown in FIG. 4A, the mesa 26 may be formed to be polygonal. In this case, as shown in FIG. 4B, the non-oxidized region 20a is also a polygon.
[0024]
Three or more VCSELs may be configured in one mesa. In the present embodiment, an example in which the mesa is extended in the one-dimensional direction is shown. However, in the mesa 26 extended in the two-dimensional direction shown in FIG. 5A, a plurality of non-oxidized regions shown in FIG. It is also possible to form a VCSEL array with a plurality of VCSELs 20a.
[0025]
In the present embodiment, the two non-oxidized regions 20a are both used as current injection regions to form an array. However, as shown in FIG. 6B, a VCSEL current injection region and A non-oxidized region 20a and a non-oxidized region other than the non-oxidized region 20a, that is, a non-oxidized region 20b that is not used as a VCSEL may be configured as a VCSEL. Of the two non-oxidized regions 20 a and 20 b, the non-oxidized region 20 a serving as a current injection region has a diameter of several μm and also forms an emission port 40 in the p-side electrode 36. The exit port 40 does not need to be formed in the other non-oxidized region 20b. In this structure, as shown in FIG. 6A, the area of the non-oxidized region 20b can be increased to make the structure more resistant to stress. Furthermore, in order to prevent current injection into the non-oxidized region 20b, a structure in which current injection is performed only in the VCSEL may be employed. Specifically, a method of providing an electrode corresponding only to the non-oxidized region 20a, or a method of preventing current injection into the non-oxidized region 20b by providing an insulating film only on the contact layer of the non-oxidized region 20b can be considered.
[0026]
In the present embodiment, an example in which InGaAs is used for the active layer has been described. However, the present invention can also be applied to a near-infrared surface emitting laser using GaAs or AlGaAs and a red surface emitting laser using InGaP or AlGaInP. Further, it can be used for blue or ultraviolet surface emitting lasers such as GaN and ZnSe, and 1.3 to 1.5 μm band surface emitting lasers such as InGaAsP. The DBR layer is not limited to a semiconductor material, and an insulating film can be used.
[0027]
In the present embodiment, the p-side electrode 36 is provided on the upper side of the upper p-type DBR layer 22, but an intra-cavity structure may be used.
[0028]
(Second Embodiment)
In the surface emitting laser array according to the second embodiment of the present invention, as shown in FIGS. 7 and 8A, three oxidized VCSELs are formed by using one mesa 26, and this mesa 26 is divided into three. The structure is arranged side by side. In this structure, as shown in FIGS. 8A to 8C, three non-oxidized regions 20 a are provided in the AlAs selective oxide layer 20 in one mesa 26. Hereinafter, the structure of the surface-emitting laser array according to the second embodiment of the present invention will be described in accordance with the manufacturing method. Note that this embodiment is an example in which the present invention is applied to a matrix-driven oxidized VCSEL array.
[0029]
First, an n-type GaAs buffer layer 11 having a carrier concentration of 1 × 10 ¹⁸ cm ^{−3 and a} thickness of about 0.2 μm is stacked on a semi-insulating GaAs substrate 9 by metal organic chemical vapor deposition (MOCVD). In addition, Al _0.9 Ga _0.1 As and Al _0.3 Ga _0.7 As are alternately stacked for 40.5 periods so that the respective film thicknesses are ¼ of the wavelength in the medium, and the carrier concentration becomes 1 × 10 ¹⁸ cm ^−3. Lower n-type DBR layer 12, undoped lower Al _0.5 Ga _0.5 As spacer layer 14 and undoped quantum well active layer 16 (thickness 90 nm Al _0.11 Ga _0.89 As quantum well layer 3 and thickness 50 nm Al _0.3 Ga _0.1 As barrier layer 4) and an undoped upper Al _0.5 Ga _0.5 As spacer layer 18, the active layer region 30 having a film thickness at the medium wavelength, and a carrier concentration of 1 × 10 ¹⁸ cm ^-3 p-type AlAs layer 20 whose film thickness is 1/4 of the wavelength in the medium, and Al _0.9 Ga _0.1 As and Al _0.3 Ga ₀₇ As on it, each film thickness becomes 1/4 of the wavelength in the medium The upper p-type DBR layer 22 having a carrier thickness of 1 × 10 ¹⁸ cm ⁻³ and a carrier thickness of 1 × 10 ¹⁹ cm ⁻³ and a thickness of 10 nm are obtained. A type GaAs contact layer 24 is sequentially laminated.
[0030]
Here, although not described in detail, a film in which the AlAs composition is changed stepwise from 90% to 30% at the interface between Al _0.9 Ga _0.1 As and Al _0.3 Ga _0.1 As in order to lower the electrical resistance of the DBR layer. It is also possible to provide a region having a thickness of about 9 nm.
[0031]
The source gas is trimethylgallium, trimethylaluminum, arsine, the dopant material is cyclopentadinium magnesium for p-type, and silane for n-type. The substrate temperature during growth is 750 ° C. without breaking the vacuum. Then, the source gas was changed sequentially, and the film was continuously formed.
[0032]
Next, the laminated film is etched partway through the n-type GaAs buffer layer 11 to form mesas 26a, 26b, and 26c as shown in FIGS. 8A to 8C, and the side surface of the AlAs layer 20 is exposed. . In order to process the mesa shape, a resist mask R was formed on the crystal growth layer by photolithography, and reactive ion etching using carbon tetrachloride as an etching gas was used.
[0033]
Thereafter, the resist mask R was removed, and only the AlAs layer 20 was oxidized from the side by water vapor in a furnace at about 400 ° C. to increase the resistance, thereby forming an oxidized region 32 and a non-oxidized region 20a. The diameter of the non-oxidized region is about 3 μm. This non-oxidized region becomes a current injection region. FIG. 8A shows a boundary line between the oxidized region 32 and the non-oxidized region 20a of the AlAs selective oxide layer 20. FIG.
[0034]
Thereafter, an n-side electrode 38 made of Au / Ge is formed on the GaAs buffer layer 11 on the bottom surface of the mesa 26. The mesa 26 and the n-side electrode 38 are etched to the semi-insulating GaAs substrate 9 by dry etching to form a groove 42, and the mesa rows 26a, 26b, and 26c are electrically insulated.
[0035]
Between the mesas 26a, 26b, and 26c, flattening is performed using polyimide 44, and p-side electrodes 36 and wirings are formed in a direction perpendicular to the mesa direction as shown in FIG. By providing the electrodes and wirings in this way, a matrix-driven oxidized VCSEL array can be manufactured.
[0036]
As shown in FIG. 8A, the surface emitting laser according to the present embodiment has three portions (non-oxidized regions 20a) connected to the crystal structure from the substrate 10 for one mesa, and one general mesa. It has higher strength against stress than the case where one oxidized VCSEL is formed.
[0037]
In the present embodiment, the mesa 26 is formed so that the non-oxidized region 20a is rectangular, but the mesa 26 may be formed so as to be circular or elliptical. In this case, the non-oxidized region 20a is also circular or elliptical.
[0038]
In this embodiment, an example in which AlGaAs is used for the active layer has been described. However, the present invention can be applied to a near-infrared surface emitting laser using GaAs or InGaAs and a red surface emitting laser using InGaP or AlGaInP. Further, it can be used for blue or ultraviolet surface emitting lasers such as GaN and ZnSe, and 1.3 to 1.5 μm band surface emitting lasers such as InGaAsP. The DBR layer is not limited to a semiconductor material, and an insulating film can be used.
[0039]
【The invention's effect】
According to the present invention, it is possible to provide an oxidation type surface emitting laser array that is easy to manufacture, resistant to stress, and having high reliability. This makes it possible to commercialize oxidized VCSELs that have high basic characteristics but are concerned about their practicality.
[Brief description of the drawings]
FIG. 1 is a perspective view of a surface emitting laser array according to a first embodiment of the present invention.
2A is a top view of the structure of the surface emitting laser array according to the first embodiment of the present invention, FIG. 2B is a cross-sectional view taken along line AA in FIG. [FIG. 2] is a sectional view taken along line BB in FIG.
FIGS. 3A to 3F are schematic cross-sectional views sequentially showing manufacturing steps of the surface emitting laser array according to the first embodiment of the present invention. FIGS.
4A is a perspective view showing a modification of the surface emitting laser array according to the first embodiment of the present invention, and FIG. 4B is a top view of FIG. 4A.
FIG. 5A is a top view showing a modification of the surface-emitting laser array according to the first embodiment of the present invention, and FIG. 5B is a surface emission according to the first embodiment of the present invention. It is a perspective view which shows the modification of a laser array.
6A is a top view showing a modification of the surface emitting laser array according to the first embodiment of the present invention, and FIG. 6B is a surface light emitting according to the first embodiment of the present invention. It is a perspective view which shows the modification of a laser array.
FIG. 7 is a perspective view of a surface emitting laser array according to a second embodiment of the present invention before electrode formation.
FIG. 8A is a top view of a surface emitting laser array according to a second embodiment of the present invention, and FIG. 8B is a cross-sectional view taken along line AA before electrode formation of FIG. c) is a cross-sectional view taken along the line B-B before the electrode formation of (a).
FIG. 9 is a cross-sectional view taken along the line AA of the surface emitting laser array according to the second embodiment of the present invention.
FIG. 10 is a cross-sectional view of a conventional oxidized surface emitting laser.
[Explanation of symbols]
9 Semi-insulating GaAs substrate 10 n-type GaAs substrate 11 n-type GaAs buffer layer 12 lower n-type DBR layer 14 lower spacer layer 16 quantum well active layer 18 upper spacer layer 20 p-type AlAs layers 20a and 20b Oxidized region 22 Upper p-type DBR layer 24 p-type GaAs contact layer 26 Mesa 30 Active layer region 32 Oxidized region 34 SiN insulating film 36 p-side electrode 38 n-side electrode 40 Exit port 42 Groove 44 Polyimide R Resist mask 90 AlAs oxide layer 91 Non-oxidized part

Claims (7)

On the substrate, an active region comprising an active layer and a pair of spacer layers sandwiching the active layer, a pair of reflective layers sandwiching the active region, and a part of the non-oxidized region provided between the pair of reflective layers are left. And a laminated portion formed by laminating an AlAs selective oxidation layer whose peripheral portion is oxidized and formed into a mesa shape,
A surface-emitting laser array, wherein a plurality of the non-oxidized regions are formed in the same AlAs selective oxide layer in the same mesa, and two or more of the non-oxidized regions are current injection regions. 2. The surface emitting laser array according to claim 1, wherein all or some of the plurality of non-oxidized regions are current injection regions. The surface emitting laser array according to claim 1, wherein the non-oxidized region is circular or polygonal. 4. The surface emitting laser array according to claim 1, wherein the plurality of non-oxidized regions are formed in a one-dimensional direction. The surface emitting laser array according to any one of claims 1 to 3, wherein the plurality of non-oxidized regions are formed in a two-dimensional direction. The surface emitting laser array according to claim 1, wherein a diameter of the plurality of non-oxidized regions is about 3 μm. The surface emitting laser array according to claim 1, wherein a plurality of the mesas are arranged.

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