JPS584995A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To equalize temperature distribution, and to extract high output by forming a diffusion layer, the central section thereof has high carrier concentration, so that currents are focussed at the central section more than an end surface. CONSTITUTION:The P<+> type diffusion layer having carrier concentration higher than a layer 10 is formed into a P<+> type diffusion layer 21 in order to reduce additional resistance up to the P-N junction 21 from an electrode 7. In this case, a layer 11 is started from a position where entering an inner section than one end surface 31, and ended at a position where entering an inner section than the other end surface 32. Consequently, there is no layer 11 in the vicinity of the end surfaces 31, 32. As a result, the additional resistance of a current path up to the junction 21 from the electrode 7 also increases in a region where there is the layer 11 in the sections in the vicinity of the end surfaces. Accordingly, currents in the vicinity of the end surfaces 31, 32 decrease more than the central section, and currents focus at the central section. However, the absorption of beams and a temperature rise are scattered to the central section and both ends because a temperature rise in the vicinity of the end surfaces and the reduction of a band gap are generated by the center of recombination formed to the surface, and high output can be extracted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser, particularly a TJ8 structure semiconductor laser.

An example of a conventional semiconductor laser of this type is shown and explained in FIG. 1. FIG. 1(a) shows its plan view, and FIG.
1 shows a cross-sectional view along A-A in the same figure (1). In Fig. 1, (1) is a GaAs crystal substrate, (2)
) is p-type Ga, -yAjyAi epitaxial layer, (
3) is Ga 1 + y As cladding layer, (4)
is a Ga1-xmlxAs active layer, (5) is a Ga1-
, AJyAs cladding layer, (6) is GaAs contact layer, symbol X, 7 indicates kl content, these are y
>x.

Note that, except for the p-type Ga 1 + yAlyAs epitaxial layer (2), the GaAs crystal substrate (1), cladding layer (3), active layer (4), cladding layer (5), and contact layer (6) are of n-type. It consists of an epitaxial layer. A portion of the central portion of the contact layer (6) has been removed as shown. The hatched area on the left side of the figure is a p-type diffusion region formed by diffusing p-type impurities such as Zn, and the region indicated by symbol (9) is a p-type diffusion region with a relatively low carrier concentration. The swelling diffusion layer, a region indicated by the symbol Ql, is a p+ type diffusion layer having a higher concentration than the p swelling diffusion layer (9). In the active layer (4), the refractive index of the layer corresponding to the p-swelled diffusion layer (9) has a larger value than the refractive index of the p+ type diffusion layer and the n-type layer on both sides, and this portion Become a guide. (7) and (6) are metal electrodes, and (21) is a p-type electrode formed in the active layer (4) by the p-swelled diffusion layer (9).
-n junction, C11) and (2) are GaAs crystal substrates (
This is a resonator end face formed on a pair of parallel side surfaces formed by 1) and the above epitaxial layer.

Here, when a forward voltage is applied between the electrodes (7) and (8), the p-n junction c! A voltage is applied across D. However, the bandgap of the active layer (4) is narrower than the bandgap of the cladding layer (31, cladding (5)), and the current flows preferentially in the active layer (4) as shown by the solid arrow in the figure. (Actually, the diffusion voltage at the p-n junction formed in each layer must be compared, but normally the diffusion potential is approximately equal to the band gap.) At this time, the p'' junction (21) is GaAs
The p-type Ga
1-. Because of the presence of the AJyAs epitaxial layer (2), no flow flows into the GaA@crystal substrate (1).

Next, regarding the flow of current in Fig. 1(a), when a forward voltage is applied between the electrodes (7) and (8), a uniform voltage is applied across the entire p-n junction (21). As a result, a uniform current flows through the entire p-ss 1m joint Q1 from one end surface G1) to the other end surface as shown by the solid line of the arrow. However, in reality, as shown in FIG. 1), the current flows across the active layer (p-n junction (2) formed in 43) below the plane of the paper.

However, in the semiconductor laser with the conventional structure shown in Figure 1, a nearly uniform current flows from one end face to the other end face of the %I)-n junction, so the temperature distribution also changes as shown by the solid line in Figure 3 (!1). As shown in the figure, it is uniform.

On the other hand, the band gap depends on temperature; the higher the temperature, the narrower it becomes, and conversely, the lower the temperature, the wider it becomes. Therefore, this bandgap is also approximately constant as shown by the solid line in FIG. 3(b). By the way, p-am! The light generated by the m-passes travels back and forth within the guide while being repeatedly reflected at the end face, but is ultimately either emitted to the outside from the end face or absorbed within the guide. In the case of absorption, the probability of absorption increases when the band gap is narrow.

Therefore, in the conventional structure described above, the temperature is almost constant from one end face to the other end face, and the band gap is correspondingly almost constant, as shown in Figure 3(a) and Figure 3(a). Therefore, it is thought that light absorption occurs at the same rate both in the center and near the end faces. However, in reality, deep recombination centers existing on the crystal surface (it is thought that oxygen at q# penetrates the crystal surface and forms deep recombination centers) reduce the absorption rate of light near the end faces. It is increasing.

Therefore, in the conventional structure shown in FIG. 1, the temperature near the end face is actually increased by absorption of this light. In FIG. 3(a), the temperature increase due to this phenomenon is shown by a broken line. If the temperature rises near the end face, the band gap near the end face narrows as shown by broken C in Figure 3 (b). This area then absorbs light more easily. Therefore, by repeating the cycle of light absorption → temperature rise → band gap decrease → light absorption,
In reality, the temperature near the end face is extremely high. In particular, when trying to increase the current to produce a large output, this temperature rise destroys the crystallinity between the ends, making it difficult to obtain a large output. In addition, since luminous efficiency generally decreases as the temperature increases, when the temperature increases near the end face, as in the case of the conventional device described above, the luminous efficiency near the end face deteriorates, and the overall luminous efficiency decreases. was there.

The present invention was made in view of these conventional drawbacks.
The purpose is to provide a semiconductor laser that enables higher output and lower threshold current.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 2 shows an embodiment of the semiconductor laser according to the present invention, and FIG. 2(a) is a plan view thereof, FIG. FIG. 2(C) shows a sectional view taken along line CC in FIG. 2(a), and the same reference numerals as in FIG. 1 indicate the same parts in FIG. The semiconductor laser of this example has a first
It is similar to the conventional semiconductor laser shown in Fig. 1 in that it forms a p+ type diffusion layer, but it
In order to reduce the additional resistance up to the -n junction Q1), a second p+ type diffusion layer 5v with a high concentration of the first p+ type is formed.

In this case, the second p+ type diffusion layer αυ has one end surface C1
It starts at a position further inside than 1) and ends at a position deeper inside than the other end face (end).

According to the structure of the above embodiment, the second p+ type diffusion layer aυ is formed on one end surface C3 as shown in FIG. 2(1).
It starts at a position slightly deeper than 1) and ends at a position slightly deeper than the other end face (to), and near these end faces 6υ# (to), the second p +
There is no shape diffusion layer aυ. Therefore, in this portion, the additional resistance of the current path from the electrode (7) to the pn junction (21) is greater than in the region where the second p+ type diffusion layer exists. Therefore, in the structure of the above embodiment, the current near both end faces Gυ, (2) is smaller than that at the center, and the current is concentrated at the center. This state is shown by the solid arrow line shown in FIG. 2(a).

However, in reality, as in the case of Figure 1, the current flows through the p-n junction (
21).

In other words, in the semiconductor laser with the conventional structure shown in Figure 1, the temperature is almost constant from one end face to the other, and the band gap is correspondingly almost constant, so light absorption occurs even in the center. It occurs at the same rate near the end faces, but in reality, as mentioned above, the deep recombination centers existing on the crystal surface increase the rate of light absorption near the end faces. Therefore, the temperature near the end surface increases due to absorption of light, and this temperature increase becomes as shown by the broken line in Figure 3(a).If the temperature rises near the end surface, the band gap near the end surface increases to It becomes narrower as shown by the broken line in Figures ~). This makes it easier for this part to absorb light, so by repeating the cycle of light absorption → temperature rise → band gap decrease → light absorption, the temperature near the end surface actually becomes very high, especially when the current In order to obtain a large output by increasing the temperature, this temperature rise causes the crystallinity between the plates to be destroyed.

On the other hand, in the semiconductor laser of the above embodiment, the current is concentrated in the center, so the temperature in the center becomes higher than near the end facets, as shown by the solid line in FIG. 4 (1). As shown by the solid line in Figure 4 (b), the bandgap of the part becomes narrower, and the bandgap near both end faces becomes wider than the central part. Therefore, light is mainly absorbed in the central part, and the bandgap near the end faces becomes wider. It becomes difficult to absorb. However, as mentioned above, in reality, the recombination centers formed on the surface cause a temperature rise near the end face and a decrease in the band gap. This surface effect is shown in dashed lines in FIGS. 4(a) and (b). As is clear from this figure, in the semiconductor laser according to the present invention, light absorption and temperature rise are dispersed in the center and both ends, and local breakage (end face breakage) as in the conventional structure is less likely to occur. Can produce large output.

Furthermore, in the conventional device shown in Fig. 1, the temperature near the end faces becomes high, so the luminous efficiency near the end faces deteriorates, and the current tends to concentrate unnecessarily in areas with high temperatures, thus reducing the luminous efficiency. A large amount of current will flow into the vicinity of the end face where the condition is poor. On the other hand,
In the present invention, the temperature distribution is averaged compared to the conventional one, so there are no local areas with poor luminous efficiency.
It is possible to obtain a semiconductor laser with good overall luminous efficiency and low threshold current.

As explained above, according to the present invention, in a semiconductor laser having a TJS structure, the temperature distribution is averaged by providing a p+ type diffusion layer at the center so that the current is concentrated at the center rather than at the end facets. This has the effect that a large output can be extracted and the threshold fL current can be reduced.

[Brief explanation of the drawing]

Figures 1(a) and Φ) are a plan view showing an example of a conventional semiconductor laser and a sectional view taken along line A-A in the same figure (!1), and Figure 2 shows an embodiment of the semiconductor laser according to the present invention. FIG. 2(a) is a plan view of the same, FIG. 2(b)
) is a sectional view taken along line B-B in Figure 2(a), and Figure 2(C)
is a sectional view taken along line (a)Q) CC in the same figure. Third
Figures (a) and Φ) are diagrams showing the temperature distribution in the guide of the semiconductor laser shown in Figure 1 and the accompanying change in band gap. It is a diagram showing the temperature distribution along the guide of the semiconductor laser shown in FIG.
2)-"""I)'-type-Gal-yAAyAs epitaxial layer,'(31-----Ga □-yAl
yAa cladding layer, (4) @ @ @ 11 Gal
-1AjXAs active layer, (51@11@@Ga
, -yAA! yAs cladding layer, (6i fist ass GaA
@ Coy tact layer % (71, (81--,. Metal electrode, (9)... p type diffusion region, wire... first p+ type diffusion region, αυ... second p+ type expanding diffusion region, 121J...p-n junction, CI junction, (2).
···End face. Agent Makoto Kuzuno - (1 other person) Figure 1II Figure 2

Claims (1)

[Claims] A GaAs crystal substrate, and at least three layers formed on one main surface of the GaAs crystal substrate: a first n-type rad layer, an n-type active layer, and a second n-type rad layer, - x
AjxAs system (0≦X<1) multilayer epitaxial layer, a pair of parallel side surfaces formed by the multilayer epitaxial layer and the GaAs crystal substrate are resonator end faces, and from the surface side of the multilayer epitaxial layer A first p-type diffusion region formed by diffusing a small amount of p-type impurity (deeper than the active layer) is provided in a part of the epitaxial layer, and the first p-type diffusion region is formed by diffusing the p-type impurity deeper than the active layer. The p-n junction formed in the layer is orthogonal to the resonator end faces and extends from one resonator end face to the other resonator end face, and the first p-type diffusion region is further provided with the first p-type diffusion region. A second p-type diffusion region having a higher carrier concentration than the p-type diffusion region and reaching at least a deeper position than the active layer is provided, and the second p-type diffusion region and the first p-type diffusion region are In a semiconductor laser having a structure in which a boundary surface formed by a p-type diffusion region in the active layer is perpendicular to the cavity end face and extends from one cavity end face to the other cavity end face,
A third p-type diffusion region formed with a higher carrier concentration than the second p-type diffusion region is provided in the second p-type diffusion region, and the third p-type diffusion region is formed on one side. What is claimed is: 1. A semiconductor laser, characterized in that the semiconductor laser starts at a position deeper into the cavity than the end face of the other cavity, and ends at a position deeper inside than the other cavity end face.