JP3246207B2 - Manufacturing method of semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a function of emitting a laser beam in a direction perpendicular to a substrate, is capable of being highly integrated, and has a surface light emission which is easily optically coupled to an optical transmission line such as an optical fiber. The present invention relates to a method for manufacturing a semiconductor laser.

[0002]

2. Description of the Related Art In recent years, a vertical cavity surface emitting laser using a semiconductor multilayer film as a reflector of a laser cavity has been actively developed due to an improvement in film thickness controllability in semiconductor crystal growth. . Unlike a conventional semiconductor laser, a vertical cavity surface emitting laser does not require the use of a cleaved surface of a crystal to form a resonator, so the manufacturing process is simplified, and mass production and large-scale integration are easy. It has the feature. Further, since the spread angle of the emitted light can be reduced by controlling the diameter of the mesa, various features such as easy optical coupling to an optical transmission line such as an optical fiber are provided. For example, the structure shown in Electronics Letters, August 1989, Vol. 25, page 1123 is common. FIG. 8 shows a sectional structure of a vertical cavity surface emitting laser. The manufacturing method is n-type Ga
N-type GaAs and A are formed on a substrate 805 made of As semiconductor.
1st reflector 804 consisting of a multilayer film of InAs and InGa
An active layer 803 including an As quantum well layer and a p-type GaAs
And a second reflector 802 formed of a multilayer film of AlAs, and a mesa structure is formed by etching for current confinement. Thereafter, electrodes are formed on the n-side and p-side, respectively.
In the case of this material system, since the output light is transparent to the substrate 805, it can be output to either the upper or lower part. FIG. 8 shows the case of the lower output, but in the case of the upper output, a window may be provided on the electrode on the second reflector 802 side.

On the other hand, a problem of such a vertical cavity surface emitting laser is element resistance. A reflector is used as a current path. A semiconductor multilayer film used as a reflector is formed by alternately stacking two materials having different refractive indexes, and each interface is a heterojunction.
Since this has a high barrier and a large number of layers,
In particular, this causes an increase in element resistance in the p-type conductivity type layer. Applied Physics Letters, September 1991
The example shown in Monthly Volume 59, page 1147 will be described. FIG. 9 is a sectional structural view of a vertical cavity surface emitting laser in which the current path area of a p-type reflector is increased in order to reduce the resistance. Here, an undercut layer 905 that can be selectively etched is provided in addition to the configuration of the conventional example. When the mesa etching of the p-type reflector 909 is performed, the area is increased, and the current constriction structure is manufactured by performing side etching on the undercut layer.

Here, the effect of the current path area on the element resistance will be briefly described. FIG. 10 shows p-type GaAs / beryllium doped with 5 × 10 18 (cm−3).
The current-voltage characteristics when a voltage is applied in a vertical direction to 12 pairs of AlAs layers are shown. Using thermionic emission theory, calculations were performed for circular mesas having diameters of 10, 100, 200, and 500 μm. Experimental data is attached to a mesa having a diameter of 10 μm. Thus, the mesa size (diameter 10 μm) usually used for a surface emitting laser is reduced to 10
It can be seen that when the thickness is increased to about 0 μm, the element resistance is effectively reduced.

[0005]

SUMMARY OF THE INVENTION The first problem is AlGa.
With N-based materials, it is very difficult to obtain a cleavage plane. AlGaN-based crystals have high hardness and cannot be cleaved especially when sapphire is used for the substrate. Therefore, when fabricating a normal edge-emitting semiconductor laser, it is necessary to form the edge using another method, for example, wet etching. This greatly affects not only the laser characteristics but also the yield and mass productivity.
A first object of the present invention is to provide a semiconductor laser having a good yield without forming an end face by cleavage.

The second problem is that the surface emitting laser has a large element resistance, and the second prior art which solves this problem also has a problem that the manufacturing process is complicated and very unstable. Has become. In particular, it is difficult to control the amount of side etching using wet etching, and the light emitting region in the active layer 806 does not have a constant size. This poses a very serious problem when designing an optical system using it practically. Further, a p-type reflector 809
Has a structure supported only by the undercut layer 805 in the minute area, and the reliability is poor.
Also, if the diameter of the mesa is increased, the current confinement effect does not appear, and the threshold current increases. A second object of the present invention is to provide a vertical cavity surface emitting laser having a large current path area and a low resistance using a stable manufacturing process.

A third problem is that when the lattice constant is not matched with the substrate, for example, in the case of an AlGaN-based substrate on a sapphire substrate, if the necessary layers are stacked in a single growth, even the active layer region is reached. Defects occur and the characteristics are degraded.
A third object of the present invention is to provide a surface emitting laser having good emission characteristics by laminating an active layer having few defects even in the case of lattice mismatch such as AlGaN on a sapphire substrate.

A fourth problem is that, when the growth is interrupted and the surface is re-grown after being exposed to the atmosphere, the surface is contaminated, the crystallinity of the next grown layer is degraded, and the reliability of the device is reduced. Or lower it. A fourth object of the present invention is to provide A
It is an object of the present invention to provide a method for growing a layer having good crystallinity even during regrowth after touching the atmosphere in an lGaN system.

The fifth problem is the stability of the polarization direction.
In a conventional vertical cavity surface emitting laser, the transmission light of the TE mode and the TM mode of the propagation light in the resonator is almost equal, and thus the oscillation light in both polarization directions is observed. Therefore, when the vertical cavity surface emitting laser is applied to a system requiring a large polarization ratio, it is necessary to insert a polarizer. A fifth object of the present invention is to provide a surface emitting laser capable of outputting laser light having a large polarization ratio by itself.

[0010]

According to the present invention, the first, the second and the third are described.
In order to solve the problem of (1), the first
Stacking a first reflector having the first conductivity type, stacking a first insulating film on the first reflector, and removing the first insulating film by removing a part of the first insulating film. Exposing a surface of the reflector, selectively growing an active layer made of a semiconductor crystal on an exposed portion of the first reflector, removing the first insulating film, Stacking a second insulating film thereon, and selecting a semiconductor layer having a second conductivity type and a current blocking layer comprising a semiconductor layer having the first conductivity type on the exposed surface of the first reflector Forming a semiconductor laser manufacturing method by a growing step, a step of removing the second insulating film, and a step of stacking a second reflector made of a semiconductor multilayer film and having a second conductivity type; In order to solve the fourth problem, Al was placed on the substrate in the chamber.
A step of growing a first crystal containing GaN, a step of growing a thin film made of InN on the first crystal, a step of taking the substrate out of a chamber, a step of processing the substrate, Manufacturing a semiconductor laser by returning the substrate into the chamber, removing the thin film made of InN while maintaining the substrate at a high temperature in an atmosphere of NH3, and growing a second crystal containing AlGaN on the substrate. In order to solve the above-mentioned fifth problem, a method for forming a substrate and a surface-emitting laser having a vertical cavity formed on the surface of the substrate, and an insulator and a metal stripe structure alternately arranged are described. A surface emitting laser is constituted by the structure having the above.

[0011]

In the method of manufacturing a semiconductor laser according to the present invention, when growing an active layer, a current confinement structure is formed by partially growing selectively on a substrate, and then a current blocking layer is further grown by selective growth. The insulating film is removed and a reflector is laminated. In the above configuration, the current confinement region can be determined by the patterning accuracy of the insulating film, so that very stable control can be performed. In addition, since it is not necessary to embed with an organic material or the like, but bury all with a crystal, long-term reliability can be secured. Furthermore, since the active layer is grown by selective growth in a minute region, even in the case of a material system that is lattice-mismatched with the substrate, strain can be relaxed and a high-quality crystal with few defects can be obtained.

In the method of manufacturing a semiconductor laser according to the present invention, a thin film of InN is formed in advance on the surface of the substrate to be regrown, and after being exposed to the air, introduced again into the chamber. Then, by keeping the temperature high, the In
The InN thin film is removed by utilizing the difference in vapor pressure between the nitride containing In and the nitride containing no In, and a good surface is exposed and regrowth is performed. As a result, a good regrown crystal can be obtained without exposing the regrown surface to the atmosphere.

Further, in the configuration of the semiconductor laser of the present invention,
A substrate on which an insulator and a metal are formed in a stripe shape plays a role of a polarizer for light that is perpendicularly incident on the substrate. By forming this structure directly on the substrate of the vertical cavity surface emitting laser, a polarization-controllable surface emitting laser can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a manufacturing process in the first embodiment. A first reflector 102 made of n-type GaN / AlN is laminated on a substrate 101 made of sapphire. Here, the thicknesses of GaN and AlN are designed so as to have a quarter optical path length of the oscillation wavelength. In the case of a surface emitting laser, the reflectivity of the first and second reflectors needs to be 99% or more, and a thickness accuracy of 2 to 3 monolayers is required. Therefore, MBE or high-precision MOCVD is required as a growth method. Here is MOCV
Method D was used. Next, a first insulating film 103 made of an oxide film
Is deposited for about 4000 angstroms by the CVD method. A resist etching mask is formed by photolithography while leaving a pattern of a size designed as a region of the active layer 104. Here, the active layer region was a circle having a diameter of 10 μm. The first insulating film 103 is etched by dry etching using carbon tetrafluoride until the first reflector 102 is exposed. Then MO
The active layer 104 made of InGaN is selectively grown by the CVD method. At this time, InGaN does not grow on the insulating film but is stacked on a circular pattern having a diameter of 10 μm. Here, the AlGaN cladding layer may be grown simultaneously. Since the active layer 104 is grown in a minute region, stress strain due to lattice mismatch with the sapphire substrate is diffused to the outside, and crystals with few defects can be stacked. Next, the first insulating film 103 is removed with hydrofluoric acid, and the second insulating film 105 made of an oxide film is formed on the active layer 104 in the same manner as described above.
To form Then, p-type GaN and n-type GaN are selectively grown sequentially. This becomes the current blocking layer 106 for performing current confinement. The oxide film is removed again, and finally a second reflector 107 made of p-type GaN / AlN is laminated. Thereafter, an electrode forming and mounting process are performed, but are omitted here.

FIG. 2 is a sectional structural view of the completed surface emitting laser. Since the sapphire substrate 207 is an insulator,
Both the first and second electrodes are formed on the reflector side. It can be seen that the current path is wide in the second reflector 203 as shown by the thick arrow, and the path area is very large. Thereafter, the current blocking layer 205
Flowed through the active layer 204 by being constricted by the second electrode 20.
Reach 8 Here, the first electrode 202 is deposited on the entire surface, and the output light 209 is extracted from the back surface of the substrate 207. Further, it goes without saying that the loss of the output light 209 can be reduced by applying an anti-reflection coating on the back surface of the substrate 207. The first electrode 202 may have a structure in which a window is provided on the active layer 204 so that output light is extracted upward. In this case, the first reflector 206
Needs to be increased. FIG. 3 shows improved current-voltage characteristics and characteristics of the first conventional example. It can be seen that the use of the method of the present invention allows the current path area to be formed larger than that of the first conventional example, thereby greatly improving the resistance characteristics. In the second conventional example, the current path area can be increased to some extent because side etching is used, but a very unstable manufacturing process is required, and mass production is difficult. In contrast, according to this method, it is possible to cope with mass production with a stable manufacturing process.

Next, a second embodiment of the present invention will be described. FIG. 4 is a cross-sectional view of a manufacturing process of the surface emitting laser according to the second embodiment, which will be sequentially described below. First, the first reflector 4 is provided on the substrate 401 in the same manner as in the first embodiment.
Grow 02. Next, an InN crystal thin film of about 50 ° is grown (A). At this time, the growth temperature needs to be slightly lowered. Once out of the chamber, the first insulating film 4
04 is deposited and patterned using photolithography and dry etching (B). After being introduced into the chamber, it is kept at about 800 ° C. in an atmosphere of NH 3. Due to the difference in vapor pressure between InN and AlGaN constituting the first reflector, only the patterned and exposed portion of the InN crystal thin film is sublimated, and the AlGaN surface appears (C). afterwards,
An active layer 405 and a second InN crystal thin film similar to the first InN crystal thin film 403 are selectively grown (D). It is again taken out of the chamber, a second insulating film 407 is deposited on the second InN crystal thin film, patterned, and returned into the chamber (E). Here, the first InN crystal thin film is removed by maintaining the same high temperature state as before, and (F) the current block layer 408 is laminated (G). The second insulating film is removed again outside the chamber (H). Finally, the second InN crystal thin film 4 is introduced into the chamber and kept at a high temperature.
06 is removed, and a second reflector 409 is grown. According to the above method, the surface emitting laser can be manufactured without exposing the active layer and the hetero interface on both sides thereof to the atmosphere.

Next, a third embodiment of the present invention will be described. FIG. 5 is a cross-sectional view of a vertical cavity surface emitting laser capable of controlling polarization. The material system is an AlGaN system. The basic configuration is the same as that of the first conventional example, but the first and second electrodes are both arranged on the front side of the substrate 506. On the back surface of the substrate 506 made of sapphire, a polarizer made of an insulating film made of an oxide film and a metal stripe made of gold is formed. The substrate on which the insulator and the metal are formed in a stripe shape plays a role of a polarizer with respect to light that is perpendicularly incident on the substrate. In a conventional vertical cavity surface emitting laser, oscillation light in both polarization directions has been observed because the transmission loss of the TE mode and the TM mode of the propagation light in the resonator is almost equal, but by using the configuration of the present invention, Thus, it is possible to obtain output light whose polarization direction is controlled by a single element. FIG. 6 shows how the output light 605 is polarized. When the surface emitting laser 601 in which the stripe structure is not manufactured is used, as shown in FIG.
3 The first polarization direction and 604 the second polarization direction) are output with almost the same intensity. However, when the stripe structure is manufactured as shown in FIG. 6B, the light emitted from the substrate side by the action of the polarizer and having the polarization directions perpendicular to each other is directed to the direction of the stripe structure 606. Because the polarization mode that vibrates in parallel is spoiled,
When the light emitted from this element is observed externally, only the output light 605 in the mode of the second polarization direction 604 oscillating perpendicularly to the stripe direction is observed. An advantage obtained by using the configuration shown in this embodiment is that it is not necessary to use a polarizing beam splitter which must be used usually when configuring an optical system. Since the output light of the semiconductor laser has two polarization modes, it is necessary to introduce some optical components in order to eliminate unnecessary polarization modes, which has caused a lot of space and cost. In the configuration shown in this embodiment, one of the polarization modes can be almost completely removed, so that an extra optical component becomes unnecessary and a great effect is expected.

Next, a method of manufacturing a polarizer according to a fourth embodiment of the present invention will be described with reference to FIG. After a surface emitting laser is manufactured by the method described in Embodiment 1 of the present invention, a thin film 4000 # of gold 704 is deposited on the entire back surface of the substrate 703. Next, a resist is applied to both surfaces of the substrate (A). A first resist 701 is applied to the front side for the purpose of protecting the surface emitting laser 702 during the subsequent steps. Only the back side is transferred by a photolithography technique to a stripe pattern having a width of about the wavelength of the emitted light and a pitch of an interval (B). Next, the back surface of the substrate is immersed in potassium iodide and
Is formed in a stripe pattern of the second resist 705 (C). Finally, an insulating film 706 is deposited on the back surface of the substrate (D), and lift-off is performed using the resist attached to the gold 704 together with the insulating film 706 deposited on the resist. At the same time, the first resist applied to the substrate surface is also removed. As described above, the polarizer is formed on the back surface of the substrate.

[0019]

According to the present invention, a low-resistance surface-emitting laser having a stable structure can be manufactured in a stable process by introducing a manufacturing process utilizing selective growth.

Further, according to the present invention, since the active layer is selectively grown in a minute region, even in the case of a lattice-mismatched material system, stress strain is diffused to the outside, and a high-quality crystal with few defects can be obtained. .

Further, according to the present invention, when the substrate is taken out of the chamber, the surface of the substrate to be regrown can be kept without being exposed to the atmosphere, so that a regrown crystal having good crystallinity can be obtained.

Further, according to the present invention, since the polarizer is manufactured on the same substrate as the surface emitting laser, it is possible to manufacture the surface emitting laser in which the polarization direction is controlled without using extra parts. Become.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a manufacturing process of a surface emitting laser according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the surface emitting laser according to the first embodiment of the present invention.

FIG. 3 is a current-voltage characteristic diagram according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a surface emitting laser according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a surface emitting laser according to a third embodiment of the present invention.

FIG. 6 is a polarization diagram of a surface emitting laser according to a third embodiment of the present invention.

FIG. 7 is a sectional view showing a manufacturing process of a surface emitting laser according to a fourth embodiment of the present invention.

FIG. 8 is a sectional view of a surface emitting laser according to a first conventional example.

FIG. 9 is a sectional view of a surface emitting laser according to a second conventional example.

FIG. 10 is a diagram showing current path area dependence of current-voltage characteristics of a GaAs / AlAs semiconductor multilayer film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Substrate 102 1st reflector 103 1st insulating film 104 Active layer 105 2nd insulating film 106 Current block layer 107 2nd reflector 201 Current path 202 1st electrode 203 2nd reflector 204 Active layer 205 Current block layer 206 First reflector 207 Substrate 208 Second electrode 209 Output light 401 Substrate 402 First reflector 403 First InN crystal thin film 404 First insulating film 405 Active layer 406 Second InN crystal Thin film 407 Second insulating film 408 Current blocking layer 409 Second reflector 506 Substrate 601 Surface emitting laser 603 First polarization direction 604 Second polarization direction 605 Output light 606 Stripe structure 701 First resist 702 Surface emitting laser 703 substrate 704 gold 705 second resist 706 insulating film 802 second Morphism 803 active layer 804 first reflector 805 substrate 905 undercutting layer 906 active layer 909 p-type reflector

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kiyoji Onaka 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A 7-231138 (JP, A) JP-A 5- 21889 (JP, A) JP-A-7-312462 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/183

Claims (7)

(57) [Claims] 1. A step of laminating a first reflector having a first conductivity type comprising a GaN / AlN multilayer film on a substrate, and laminating a first insulating film on the first reflector. Performing a step of removing a part of the first insulating film to expose a surface of the first reflector; and selectively growing an active layer made of InGaN on an exposed part of the first reflector. A method of manufacturing a semiconductor laser, comprising: a step of laminating a second reflector having a second conductivity type and comprising a GaN / AlN multilayer film. 2. A semiconductor device comprising a semiconductor multilayer film on a substrate.
Stacking a first reflector having the first conductivity type, stacking a first insulating film on the first reflector, and removing the first insulating film by removing a part of the first insulating film. Exposing a surface of the reflector, a step of selectively growing an active layer made of a semiconductor crystal on an exposed portion of the first reflector, a step of removing the first insulating film, Second on active layer
Stacking an insulating film, selectively growing a current block layer made of a semiconductor layer having at least a first conductivity type on an exposed surface of the first reflector, and removing the second insulating film And a second process comprising a semiconductor multilayer film.
A method of manufacturing a semiconductor laser, comprising: stacking a second reflector having the conductivity type of (1). 3. The first and second reflectors are each formed of a GaN / AlN multilayer film, and the active layer is formed of InG.
3. The method for manufacturing a semiconductor laser according to claim 2, comprising aN. 4. A step of growing a first crystal of GaN / AlN on a substrate, a step of growing a thin film of InN on the first crystal, and depositing an insulating film on the thin film of crystal. Performing the step of: patterning the insulating film; removing the crystalline thin film of InN while maintaining the temperature at a high temperature in an atmosphere of NH 3;
A crystal growth method, comprising a step of growing a second crystal made of AlN. 5. A step of laminating a first reflector made of GaN / AlN on a substrate, and a step of depositing InN on the first reflector.
Stacking a crystalline thin film consisting of: a step of depositing an insulating film on the crystalline thin film; a step of removing a part of the insulating film to expose a surface of the thin film; Removing the crystalline thin film made of InN, keeping an active layer made of InGaN on the first reflector, and removing the first insulating film;
Laminating a second insulating film on the active layer, selectively growing a current block layer made of a semiconductor layer having at least a first conductivity type on an exposed surface of the first reflector; Removing the second insulating film;
A method for manufacturing a semiconductor laser, comprising a step of laminating a second reflector made of AlN. 6. The method of manufacturing a semiconductor laser according to claim 5, wherein all the regrowth involves growing and removing said crystal thin film made of InN. 7. The crystal growth method according to claim 4 , wherein a growth chamber for growing said crystal thin film is a growth chamber different from a step for depositing said insulating film.