JPS6356981A - Compound semiconductor laser - Google Patents

Abstract

PURPOSE:To realize reduction of threshold current, and stabilization and uniformity of characteristics, by a method wherein current limiting by utlizing crystal anisotropy of carrier density or current concentrating by forming a current path is performed. CONSTITUTION:On the main surface of a substrate 1, for example, GaAs single crystal substrate, an inclined plane 2 is formed. Thereby the (100) crystal face and the one different from (100) face are made to face a main surface 1a. On these crystal surfaces, a III-V compound semiconductor layer is grown by, for example, an organic metal vapor phase epitaxy which is so-called MOCVD. A current concentration region 3 is formed in the manner in which a current path is limited by utilizing the difference of carrier density from each crystal surface to a growth region. Therefore laser light emission is generated by forming a local part in which the density of injected carrier is large, that is, a part of large gain. Thereby, a gain-guide type can be formed wherein the threshold current is small, and uniform stable characteristics are realized.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to compound semiconductor lasers.

[Summary of the invention]

In the present invention, a substrate is provided with a slope formed on one main surface so that a (100) crystal plane and a crystal plane other than the (100) crystal plane are exposed, and a 1 m compound half body is epitaxially grown on this substrate. A compound semiconductor laser is constructed in which a region with different carrier concentrations is formed in the epitaxial growth region of each crystal i1+i so that a current path is formed in a limited manner, and reliable current confinement due to the difference in carrier concentration is achieved with a narrow width. °ζ can be done with threshold flow 1
Aim to improve characteristics such as reducing th.

[Conventional technology]

Conventionally, in a gain-guided semiconductor laser, a current confinement means is provided to concentrate the current in the oscillation region of the active layer, forming a portion where the carrier density is large, that is, a portion where the gain distribution increases steeply. form a gain waveguide function.

When constructing such a gain-guided semiconductor laser, if the current is constricted, a high resistance region is selectively formed by implanting ions such as energized protons, boron, etc., or a current blocking region is formed by a pn junction. In other words, a current confinement means is provided so that the current path is limited by forming the ohmic contact portion of one of the opposing electrodes of the laser diode in a limited manner by insulating it with 1 m of insulation.

However, in either case, there is a problem in that it is difficult to concentrate the current sufficiently, making it difficult to sufficiently reduce ith and stabilize the characteristics.

[Problem that the invention seeks to solve]

The present invention aims to solve the problems of sufficiently reducing 1th and stabilizing the characteristics by making it possible to reliably and reproducibly perform current concentration, that is, current confinement, in the gain-guided semiconductor laser described above, for example. It is something.

That is, in the present invention, III-V group compounds such as A12 y Ga1-xAs or In y Ga
x-y As (0≧X.

When y>1) is epitaxially grown by metal-organic chemical vapor deposition (MOCVD), M under the same conditions depends on the crystal plane orientation of the epitaxially grown substrate surface.
It was discovered that the carrier concentration differs in OCVD, and by utilizing this difference in carrier concentration to obtain a current confinement effect, it is possible to form a sufficient current concentration in a narrow portion with good reproducibility. In this way, the above-mentioned problems are solved.

[Means for solving problems]

As shown in FIGS. 1 and 2, the present invention is achieved by forming a slope (2) on the - upper surface so that the +100) crystal plane and another crystal plane different from the (100) crystal plane are the main planes. (1
a) A substrate (11, for example, GaA) provided facing the side
A single crystal substrate is provided, and an m-v group compound semiconductor layer is epitaxially grown on each of the above-mentioned crystal planes by, for example, metal organic chemical vapor deposition (MOCVD), and the growth from each crystal plane and the carrier concentration in the region are Current concentration region (3)
is formed to locally form a portion with a large injected carrier density, that is, a DI portion with a large gain, so that laser emission occurs.

In addition, MOCVD is good (as is known, group III elements,
8l, Ga + In, ′ζ is the organic metal gas trimethylaluminium gallium (TMG),
) or triethylaluminum (TE^), triethylgallium (TEG), )liethylindium (TEI)
) etc., group Ⅰ element As. As for P, its hydride arsine ASH3 + phosphine Plb is used. Then, these are fed into a reaction vessel at a required ratio of group V raw materials to group (I) raw materials (hereinafter referred to as V1m ratio). In the reaction vessel, the substrate with the above-mentioned slope formed thereon is placed at a required substrate temperature Ts, and on the front side of the substrate, the ■-■ group compound is formed on the substrate surface by the thermal decomposition of the above-mentioned raw material gas. Epitaxially grow a semiconductor layer.

[Effect]

As mentioned above, in the present invention, the crystal anisotropy of the carrier concentration is used to limit current or form a current path to achieve current concentration, so selection of crystal planes ensures current concentration. Since it can be formed into a pattern with a predetermined size and shape, it is possible to reduce ILh, stabilize characteristics, and improve uniformity, for example.

Let's take a look at the crystal anisotropy of this carrier concentration.

Figure 3 shows the measurement results of the carrier concentration, that is, the concentration of carbon C as a xerogen and the mixed concentration of Si as a donor, when the V/III ratio is changed.
In this case, the S compound semiconductor layer was formed by MOCVD using trimethylaluminum, trimethylgallium, and arsine as source gases on a GaAs substrate with a temperature fTs = 800°C. This is the case when measurements were taken. In the same figure, the mark Mu is the (311) B crystal plane (i.e. (311)
When plotting the measurement results when the above-mentioned βGaAs thread MOCVD semiconductor layer was formed on a GaAs single-crystal substrate with As crystal plane), the n-type characteristics were lost in both cases, and in this case, the V/III ratio was When the odor was decreased, the p-type did not occur even when the odor was decreased. In addition, in the same figure, the ζ○ marks and ・marks indicate the conventional (100)
The figure shows the carrier concentration versus V/LIT ratio when a similar semiconductor layer is formed by MOCVD on a GaAs substrate, where the ◯ mark indicates p-type characteristics and the e mark indicates n-type characteristics. In addition, in the same figure, the mouth seal and I seal are (311)A, respectively.
(That is, (311) Ga crystal plane) The measurement results of carrier concentration with respect to each V1m ratio in a semiconductor layer formed by similar MOCVD on a GaAs substrate with (311) Ga crystal plane are plotted. It is a model.

As is clear from FIG. 3, the carrier concentration differs depending on the crystal plane of the substrate even though MOCVD is performed under the same conditions. For example, when m-v group semiconductors are formed on (100) and (311) substrates by MOCVD, V/I
It takes on a form. This is because carbon C enters the Ga site and acts as an acceptor. Furthermore, if the V1m ratio is increased, the amount of donors such as silicon St increases, and the carrier concentration increases. That is, formed on a (100) substrate? In the case of l0CVD semiconductor layer, ■/I! p-type when I ratio is around 80-120
Compared to n-type inversion, when MOCVD semiconductor I semiconductor is formed on a (311) B substrate, even if the ■/■ ratio is made sufficiently low and the surface becomes cloudy, n-type − p
No type reversal was observed, and the resistance was sufficiently improved. Therefore, if the V/III ratio is selected to be a sufficiently small value, for example, 100 or less, the amount of both donor and acceptor impurities mixed in can be reduced, and a high-resistance semiconductor layer with a low carrier concentration can be constructed.

In addition, FIGS. 4 and 5 show that AQ is placed on the (311)B substrate.
The case where a non-doped MOCVO semiconductor layer of XGa, -XAs (x = 0.33) is formed and the case where
) Substrate ``Non-doped similar A! Qx Ga1-x
These are photoluminescence spectra at 4K when an MOCVD semiconductor of As (x-0,33) is formed. In these, V/I[I=13
This is the case where it is set to 5.

In Figures 4 and 5, the peak b on the right side of °ζ, that is, on the long wavelength side, is due to the transition from residual toner to carbon acceptor, and the peak a on the left side, that is, on the short wavelength side, is due to the transition of carbon acceptor to residual donor. Constrained half-width 6.516me
This is the exciton beak of V. 4 and 5, it is clear from the difference in the relative strength of the left and right peaks ab, i.e., the exciton peak and the peak of the donor-acceptor pair emission caused by residual impurities. 3
11) The MOCVD semiconductor layer formed on the B substrate is (1
00) It can be seen that compared to the semiconductor layer formed on the substrate, '53' fJ due to residual carbon is small and the crystallinity is excellent.

According to the research and consideration of the present inventors, carbon l-no-j dyeing is
(311) B side heno MOCvD is the smallest, followed by (111) 8 side, (100) side, and (111) convex side.

(311') It was confirmed that as MOCVD was performed on the A side, the contamination gradually increased.

Now, typical crystal orientations of GaAs single crystal substrates (100)
.

n-type 8j2 n, 33 doped with Se as an n-type impurity for (311) 8 and (311) B, respectively.
Gao,s? Table 1 shows the results of measuring the carrier concentration and mobility of each semiconductor layer when the ^S compound semiconductor layers were simultaneously formed by the same MOCVD method.
Shown below.

Se-doped n-Aj! 0,33 Gao, 6
In the case of 7^S Table 1 Similarly, for the different crystal planes (100), (311)8, and (311)B of the GaAs1i crystal substrate, Zn-doped p-type AN O,:13 Gao,
Table 2 shows the measurement results of the carrier concentration and mobility of each semiconductor layer when gt As compound semiconductors were simultaneously formed by the MOCVD method.

Zn-doped p-8l o, g3(:ao, ev
In the case of ^S Table 2 As is clear from these tables, carrier concentrations differ depending on the substrate crystal plane in the same n-type or p-type compound semiconductor. As a result, in the apparatus of the present invention, where different crystal planes are formed on the substrate (1) and semiconductor layers are epitaxially grown on these different crystal planes, parts of the same semiconductor layer with different resistivities are separated. It can be seen that the current concentration region (3) is locally formed.

〔Example〕

An example of a gain-guided semiconductor laser according to the present invention will be explained with reference to FIG. In this example, Zn
GaAs substrate (1) having a doped p-type, and its raw 11u(la) having (100)Vlli
is provided, and on its -main surface (1a), for example, (311
) The convex surface has an exposed slope (2), and the bottom surface has (100)
Form a striped recess (toward) facing the surface. Then, on the main surface (1a) of this substrate (1), a p-type buffer layer (4) of the same conductivity type as the substrate (1) and a p-type first cladding l1=( 5) and p or n
Low impurity concentration or non-doped activity 1j# (
61 and the substrate (n-type second cladding i!f!7 of a conductivity type different from that of 11) and, for example, a cap layer of the same conductivity type as dirt (
8) are epitaxially grown by MOCVD in the same continuous operation by controlling the feed gas.

Here, the buffer layer (4) is
The first cladding layer is also formed by a Z
n-doped e.g. A l O, 33Gao, s v A
The active layer (6) is formed of a GaAs layer, the second
The cladding layer (7) is doped with SO.
The cap layer (8) may be formed from a Se-doped GaAs substrate or the like.

Further, as raw material gases for this MOCVD, (1) TMA and TMG gases are used as the six raw materials, and arsine is used as the raw material of the group (2) S.

In this case, the active l@(61 odor ζ is ,
As is clear from Table 2, the carrier concentration due to the growth region from both slopes (2) is formed as a nearly flat surface.
A current concentration region (3) having a lower resistivity than the other regions grown from the (100) plane is formed respectively, and both regions (8) are formed as follows.
As shown with diagonal lines in FIG. 1, the active l'fi (bl) is formed so that it is narrow or its tips coincide.

Further, on the cap layer (8), °ζ5i0
A second insulating layer (9) is formed, and electrode windows (9a) are formed in stripes at opposing positions on the tip of the region (Ell), and one electrode (10) is formed through this window (9a). It is made to be ohmicly adhered.Also, the substrate (
A counter electrode (11) is formed on the other surface of 1).

According to such a configuration, the current concentration regions U) whose specific resistance is smaller than other regions create stripe-like current concentration regions, that is, injection carrier density, in the active layer (6) at the tips of these regions U). A human part with large gain can be formed and laser emission can be performed.

In the above example, the current concentration region (3) is the growth region from the slope, but in some cases, the growth region from the slope (2) is the high resistivity region and the current limitation region. can do. An example of this case is shown in FIG. 7173 corresponding to FIG. 1 are given the same reference numerals and redundant explanation will be omitted, but in this example, the substrate (1) is a p-type semiconductor layer on an n-type GaAs single crystal substrate (IA). (IB) is epitaxially grown. Then, by selectively etching a part of this p-type semiconductor 1m (IB) in a stripe pattern, recesses (31) were provided on both sides, with the (311) A side facing and the bottom surface being (100) blood. In this case, the p-type semiconductor 1 (IB) is made to act as a current stop region, and in some cases, the p-type semiconductor 1 (IB) is made to act as a current stop region, and in some cases, the p-type semiconductor 1 (IB) is It has a small bandgap and a high refractive index, and serves as a light absorption agent that absorbs light seeping out from the active layer (6).

In this case, the growth region grown from the crystal plane (311) A plane of the slope (2) of the recess θ3) is
Since the carrier concentration is lower than that of the region grown from 00), it becomes a crystallization resistance region (12), so the @ region (
12) becomes a current concentration region (3), and at the tip of this region, the active layer φ) has a high stripe-like injected carrier density, that is, a stripe-like shape with a large gain, that is, a stripe-like shape due to gain waveguide. This is to form a resonator, that is, a laser emitting section.

In this case, the current i! ! ! By appropriately selecting the distance between the semiconductor layer (IB) and /1111000) which performs the cutting, the light seeped out from the active layer (6) mentioned above is absorbed here, and a refractive index waveguide function is also provided. It is also possible to have a configuration in which:

Furthermore, in the above example, the (100) plane and the (311
) In this case, the A-plane is formed on the main surface (la) side of the substrate (1), and the current is concentrated by utilizing the difference in carrier density in the crystal growth area from both sides. , other crystal plane combinations may also be utilized. In addition, the formation of the four parts (13+) is performed by chemical etching with crystal anisotropy, for example, on the slope (2) (
111) It is also possible to cause the A side to occur. still,
In this case, the crystal plane growing on the (111) convex surface is (31)
1), (511) A, and so on, so that it is possible to achieve substantially the same effect as in the case of (311) A, for example.

Further, as described above, in the present invention, the current path is limited by utilizing the difference in carrier concentration based on the difference in the crystal growth plane. ) - selectively form sheet resistance regions etc. by implanting protons or boron ions on both sides of the striped laser emitting region i61
Various modifications and changes can be made to the illustrated example, such as a configuration in which the current concentration effect can be more reliably achieved by forming the current concentration effect.

〔Effect of the invention〕

According to the present invention, since the current concentration region is formed by utilizing the dependence of the carrier concentration on the crystal plane, it is possible to reliably form a narrow current concentration region, and as a result, +th is small and uniform and stable. A semiconductor laser having a basic configuration of a gain-guided type semiconductor laser having such characteristics can be constructed.

Furthermore, according to the configuration of the present invention, groups J having different crystal planes
i(11) is formed by, for example, four parts (:3) by etching, but since the formation of these four parts is performed in the MOCVD eviaxial growth curve of each semiconductor layer, each of the above, including buffer I-(4+) For semiconductors, MOCVD work can be performed continuously.Therefore, discontinuous parts are formed between each MOCVD semiconductor layer, unnecessary oxide films are interposed, and other inconveniences such as deterioration of crystallinity and low workability can be avoided. It never invites people.

[Brief explanation of drawings]

Figures 1 and 2 are enlarged cross-sections of compound semiconductor lasers according to the present invention, respectively, and Figures 1 and 3 are graphs showing the amount of Group Ⅰ raw material gas in MOCVD for each crystal plane selection used to explain the present invention. The measurement results of the carrier concentration when changing the ratio of the group raw material gas amount are shown in the Neo curve diagram, Figures 4 and 5, "1" are (311) BIA slope and (100), respectively.
This is a photoluminescence spectrum of a semiconductor layer formed on a substrate by MOCV. (1) is the substrate, Qq) is the recess, (2) is the slope, (4) is the buffer layer, (5) and (7) are the first and second cruts l-1 (6) is the occupancy y day, (8) is the cap °Im
, (10) and (11) are electrodes.

Claims (1)

[Claims] - A slope is formed on the main surface, and the {100} crystal plane and the {100}
}On a substrate provided with another crystal plane different from the crystal plane,
1. A compound semiconductor laser characterized in that a compound semiconductor layer is epitaxially grown so that a current path is restricted by a difference in carrier concentration in each epitaxial growth region on both crystal planes.