JPS6017977A - Semiconductor laser diode - Google Patents

Abstract

PURPOSE:To obtain a crystal structure of a laser diode element which can increase its output without loss of the substrate properties of the laser diode by concentrating the applied current only at the active stripe. CONSTITUTION:A clad layer 12 and a flat raised guide layer 13 bent by a groove, formed of an N type AlGaAs are arranged on an N type GaAs substrate 11 formed with a groove 91 in the prescribed size at the position for disposing a cavity. Further, an active layer 15 formed of AlGaAs, a clad layer 15 formed of P type AlGaAs, and a cap layer 16 formed of P type GaAs are arranged to expose the surface of a guide layer 13 by forming grooves at the end and both sides of active stripes 92. 2-layer block layers 117, 127 made of P and N type AlGaAs and a cap layer 137 made of P type GaAs are arranged to cover the layers 13-16. When only the active strip 92 of the center is electrically connected, the light emitted from the layer 14 of the strip 92 is propagated through the guide layer, and is guided to the end, i.e., the reflecting surface of the element crystal chip.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an element structure of a semiconductor laser diode, and particularly to an end-face buried type element crystal structure for obtaining high optical output.

In the confectionery crystal of a semiconductor laser diode, there are usually many interface states near the end face (reflection face), so the injected carrier density decreases and the crystal becomes an absorption layer for laser light. In the vicinity of the end face, heat is generated due to light absorption, resulting in a decrease in band gap energy and further increase in light absorption. It is said that at high optical output densities, when a certain optical output limit is exceeded, the crystal on the reflective surface reaches its melting point due to the positive feedback action of light absorption → heat generation → light absorption, and eventually melts. This limiting optical output is called critical optical output (POOD), and the size of i'oon closely depends on the structure of the element crystal. The first method is to reduce light absorption at the end face and increase PaoD'fc.
There is an element crystal structure of an end face buried type as shown in the figure.

Figure 1 is a conceptual diagram for explaining a conventional edge-embedded laser diode element.
Al()aAs)/Gallium arsenide (GaAs)
Taking the system as an example, a cross section in a direction parallel to the cavity is shown. That is, AI Ga A is deposited on the n-type GaAs substrate 1.
A double heterojunction consisting of an active layer 4 and cladding layers 2 and 5 made of
- is electrically connected to the external electrode 8, and a diffusion layer and the like for current confinement are formed directly above the cavity of the cap layer. Cladding layers 2 and 5 are formed on both end surfaces of this cavity.
/JGaAs with band cap energy similar to
An end face buried layer 7 consisting of the following is provided. Therefore, the end face buried layer 7 has a larger band gap energy than the active layer 1.
It is said that the above-mentioned FOOD can be increased because the light absorption at the end face can be suppressed to a small extent by the arrangement of the elements.

However, in the conventionally known structure as described above, the light guide portion serving as the visiting body waveguide is interrupted at the buried interface. For this reason, the position of the resonant surface moves away from the original guide portion, and the diffraction refraction increases. Therefore, the threshold current (I+h
) increases, the differential efficiency (ηD) decreases, and the basic characteristics of the laser diode are completely degraded. Therefore, even though the structure was originally designed to be able to handle high optical output by improving the critical optical output 1:'OOD k, not only is it not possible to obtain sufficient optical output, but at high current density. When put into practical use, there is even a concern that product reliability may be compromised. In addition, the position of the beam waist of the laser beam cannot be controlled due to positional variations when cutting out the element crystal, that is, forming the open face (reflecting face), so it has a drawback that it is difficult to use in practice.

The present invention has been made in view of the above, and is a novel laser diode confectionery that eliminates the drawbacks of the conventional end-face buried element crystal structure and enables high output without impairing the basic characteristics of the laser diode. The purpose is to provide the crystal structure of.

According to the present invention, on a compound semiconductor substrate of one conductivity type in which a groove is formed, a cladding layer having a curved cross section at the groove portion of the same conductivity type as the substrate, and a guide having a plano-convex cross section at the groove portion. The active layer, the cladding layer and the first cap layer, which are of the opposite conductivity type to the substrate, are cut and removed on both end faces in the direction of the cavity, and the active layer is disposed on the guide layer over the entire surface of the substrate. In order to completely form stripe-like protrusions in the upper part of the formed groove, both sides of the stripe-like protrusions are removed in grooves to partially expose the surface of the guide layer. Two blocking layers of the opposite conductivity type and the same conductivity type as the substrate are sequentially disposed on the top of the striped protrusions except for the upper part of the striped protrusions, and a block layer of the same conductivity type as the substrate is further disposed on the surface of the first cap layer where the striped protrusions are exposed. The block layer has a cap layer of Wc2 with opposite conductivity to the substrate disposed so as to cover the entire surface of the block layer, and only the striped protrusions separate the active layer from the main layer.
5= A semiconductor laser diode having an element crystal structure characterized in that electrical connections are made is obtained.

Below, the present invention will be described using drawings. ! G
This will be explained in detail using an example of an aAs/GaAs system.

FIG. 2 shows the crystal structure of a semiconductor laser diode device according to the present invention. FIG. 2 (al) is a sketch diagram conceptually showing the relative positional relationship of the element crystal structures in order to facilitate understanding of the present invention. FIG. It shows a cross section, that is, a cross section in a direction parallel to the cavity, and corresponds to Fig. 1 showing the conventional structure. It shows a cross section in the orthogonal direction.

The structure of the present invention is formed on an n-type GaAs substrate 11 (C
,, n-type Al! When a cavity made of GaAs is seen in a modified cross section, a curved cladding layer 12 and a plano-convex guide layer 13 are provided, and an active layer 14 made of A/GaAs is provided.
．． P type AA! The cladding layer 15 made of GaAs and the @1 cap layer 16 made of P-type GaAs are attached to the end face portion and (a) as shown in FIG. 2(a) or (b).
Or (as shown in CJ, grooves are formed on both sides of the active strip 1920 so that the surface of the guide layer 130 is exposed, and these are the guide layer 13, the active layer 14, the cladding layer 1)
5. To cover the first cap layer 16, two layers 117 and 118 made of P-type and 11-type AlGaAs and a second layer made of P-type GaAs are formed in the shape shown in FIG. 2 (bl and FC). This is achieved by disposing two cap layers 127.

Here, it is assumed that the A7 mixed crystal ratio of each layer satisfies the relationship: active layer>guide layer>cladding layer=block layer.

The theorem of the structure of the present invention is that after a groove 91i is formed in advance on an n-type (ia AS substrate 11 using photolithography), an n-type cladding layer 12, a guide layer 13, an active layer 14, a p-type cladding layer 15 After performing liquid phase epitaxial growth of 5 consecutive layers up to P die engraving 1 cap layer 16, dry etching using halogenated carbon and sulfuric acid (H, 804)/hydrogen peroxide (HtUs) based ettender solution were used. A shape as shown by the dotted line in FIG. Aluminum can be obtained by continuous growth using a nine-liquid phase epitaxial technique. Here, each epitaxial layer of aluminum (
AAi) A desired composition can be obtained by adjusting the mixed crystal ratio and the type and concentration of impurities by adding them in advance or during the liquid phase epitaxial growth. N-type impurities for GaAs include tin (Sn), tellurium (Te), and silicon (Si).
However, as P-type impurities, germanium (G, sub-M (
Magnesium (Mg) is commonly used. Furthermore, it is known that liquid phase epitaxial growth tends to grow more easily in narrow groove-like portions. During the second liquid phase epitaxial growth, that is, the growth of the two-layer blocks 117, 127 and the second cap layer 137, the growth of the groove portion is fast, so the solute around the groove is attracted into the groove, and the layer thickness around the groove is reduced. Become thin. The striped protrusions (i.e., active stripes) 92 located on the optical guide portion (i.e., directly above the grooves 91 formed in the substrate of the guide layer 13) have a narrow width (usually on the order of several μm in a laser diode element). , the above effect is so remarkable that the start of epitaxial growth is delayed compared to the area having wide surfaces on both sides. Therefore, the above P type kl
If the block layers 117 and 127 consisting of two layers of GaAs and n-type A45GaAs are grown, block layers will be formed on the wide surface areas on both sides as shown in Fig. 2(C), but the active layer in the center will be A state in which no block layer is formed on the striped portion (b) can be realized. Next, P-type Ga
If the second cap layer 137 of A, s is grown over a relatively long period of time, only the central active stripe portion 92 is electrically connected. Further, by forming a conventional electrode metal layer and then opening the structure, the structure of the present invention as shown in FIG. 2 can be obtained.

If the present invention is fully implemented, the active layer 14 of the active stripe portion 92
Since the emitted light propagates through the guide layer, it is guided to the end face or reflective surface of the element crystal chip. Therefore, it is possible to eliminate the diffraction refraction caused by the position of the resonant surface moving away from the guide part, which was a big problem in the conventional structure. ). Furthermore, the problem of controlling the beam waist position due to variations in the aperture position during chip cutting is essentially eliminated by guiding the light to the end face of the crystal chip.

In addition, in a layer with a small Al mixed crystal ratio, the band gap energy is large, so as mentioned above, light absorption is small and the critical light output Pao
It is possible to increase o-q. In the structure of the present invention, the vicinity of the reflective surfaces (resonant surfaces) located at both ends of the cavity is composed of the guide layer 13, cladding layer 12, and block layer 117, which have a lower Al mixed crystal ratio than the active layer, so the critical optical output P . .

D can be greatly improved.

Furthermore, the structure of the present invention? : If taken, two-layer block layer 117
．． Current confinement by 127 works extremely effectively. In other words, the current applied to the electrode metal film 18 is blocked) @11
7 and 127, and is concentrated only in the active stripe portion 92 of the second cap layer 16, and is injected only into the active layer 14 existing in the active stripe portion without leaking to the surroundings. Therefore, the threshold current density (J+h) for laser oscillation is easily reached and the reactive current is reduced, so the so-called threshold current ■4- b is small.
Current usage efficiency is good and relative heat generation is reduced.

Furthermore, because of the above-mentioned effect, it is possible to limit the number of laser diode elements with sufficient optical output, so the entire width S of the active stripe can be made shallow, and the horizontal direction angle of incidence θ11 of the emitted laser beam can be increased. I can do that. Generally, in a laser diode device, the active layer thickness is extremely thin, about 0.1 μm or less, so the far-field pattern of the laser beam takes an elliptical shape, which is an ellipse in the vertical direction.The closer this is to a perfect circle, the more efficiently the laser beam can be used in practical use. can. Therefore, by reducing the width S6 of the supernatant stripe portion and increasing the horizontal beam direction angle according to the present invention, the far-field image of the laser beam approaches a perfect circle, and the practical efficiency of the laser beam increases accordingly. There is also the additional effect that a product that is easy to use as a diode can be obtained.

The structure, operation, and effects of the present invention have been described in detail above, but by fully implementing the present invention, a product with high output, that is, high critical light output, can be realized without any loss in the basic performance as a laser diode, and the threshold Since the current is small and high efficiency can be used, the temperature rise during product use is small, making it possible to create highly reliable laser diodes.

Although the present invention has been explained by taking examples of Ad Ga and As/GaAs laser diodes, it goes without saying that it can also be applied to indium gallium arsenide phosphide (InGaAsp)/inshu phosphorous (InP) laser diodes and others. Moreover, the same effect can be obtained even if the conductivity type of each layer is reversed.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of a conventional active layer edge-embedded semiconductor laser diode device structure (cross-sectional view parallel to the cavity).
. FIG. 2 is a conceptual diagram of the active layer edge-embedded type semiconductor laser diode element structure according to the present invention, and the second figure (al is a structural sketch diagram for explaining the present invention as a whole, and FIG. 2 (1)) shows the cavity and Cross-sectional view in the parallel direction (Y-Y' direction), Figure 2 (
C) shows a cross-sectional view in a direction perpendicular to the cavity (X-X' direction). 1.11...ll type GaA, S substrate, 2, 1
2 ・-・-・11 type AlGaAs cladding layer, 1
3...fl type A, 1GaAs guy)"Jtii
, 4, 14---AeGaAs active layer, 5
,15°...P fJ kl GaAs cladding layer, 6,16...P-type GaAs cap layer or first cap layer, 117...P-type AdGa
As block layer, 127...nm AlGaAs
37-, P-type GaAS second
Cap layer, 8.8', 18.18'... Electrode metal film, 91... Substrate groove for forming electric waveguide,
92 (b)...Active stripe section. Helmet 1

Claims (1)

[Claims] A cladding layer having a curved cross section at the groove portion and a guide layer having a plano-convex cross section at the groove portion and having the same conductivity type as the substrate are formed on a compound semiconductor substrate of one conductivity type in which a groove is formed. Disposed over the entire surface of the substrate, an active layer on the guide layer, a cladding layer and a first cap layer having a conductivity type opposite to that of the substrate are cut and removed at both end faces in the cavity direction, and then formed on the substrate. Then, in order to form a stripe-like protrusion in the upper part of the groove, both sides of the stripe-like protrusion are removed in a groove-like manner so that the surface of the guide layer is partially exposed. , a two-layer block layer of the opposite conductivity type and the same conductivity type as the substrate is disposed in order on this except for the upper part of the stripe-shaped protrusion, and further a first block layer with the stripe-shaped protrusion exposed
A second cap layer of the opposite conductivity type to the substrate is disposed so as to cover the entire surface of the cap layer and the block layer of the same conductivity type as the substrate.
1. A semiconductor laser diode having an element crystal structure characterized in that the main electrical connection to the active layer is made only by the striped protrusions.