JPS58225683A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain the laser having excellent oscillation made characteristics by a method wherein a V-groove is formed on an InP substrate, and an InGaAsP layer is epitaxially grown in such a manner that it is astriding the groove while it is being contacted to the top part of the groove, thereby enabling to oscillate at a low threshold current. CONSTITUTION:A V-groove 2 is cut in the center part on the surface of the InP substrate 1 having the surface (100), an InP layer 7 is epitaxially grown on the bottom face of said groove 2 and, at the same time, a grown layer 8 is generated on the flat part 1a on the surface of the substrate 1. Then, for the purpose of filling up the V-groove 2, an InGaAsP layer 11 is grown on the whole surface including the groove 2, said layer 11 is contacted to the upper parts 2a and 2b of the V-groove 2, and above is brought into the state wherein the layer is astriding the groove. Subsequently, an InP layer 12 is epitaxially grown on the layer 11, and the entire surface is flattened by removing the stepping located between the internal part and the external part of the V-groove 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser that oscillates with a low threshold current and has excellent oscillation mode characteristics.

Semiconductor laser oscillates at a low threshold current, generates less heat in the active layer, and has good high-temperature operation? It is possible to reduce heat generation, and to keep heat generation low,
In order to obtain a semiconductor laser that oscillates with a low threshold current, efforts are made to reduce σ and the cross-sectional area of the active region in the cavity length direction. This reduction in the cross-sectional area in the resonator length direction also leads to the creation of a semiconductor laser with excellent multimode characteristics.

On the other hand, a liquid phase epitaxial method is known as a general method for manufacturing semiconductor lasers. This method (a1) allows epitaxial growth with good crystallinity, is simple, and has the advantage of being able to grow as thin as about 1 μm in growth layer thickness.

However, it is not easy to control the width direction required for the active layer of a semiconductor laser, and for this reason, a two-step growth method is generally used, and this method can be broadly divided into two types. be.

The first method is to grow a normal double heterojunction structure in the first growth, remove the active layer by etching on both sides leaving only a narrow width, and then fill in both sides with the second growth. Yes, that-examplettx T, Tauka
da (T, Tsukada), J, Appl,
.

Phya (Journal, Applied, Phiztsux)
Volume 45, 1974, page 4899.

In addition, in the second method a, the epitaxial substrate on which the -th growth has been completely performed (or it is better to just use a substrate) is formed into a groove hole O1 with a narrow t/c RLJ, and then the second growth is performed normally within this groove. A double heterojunction structure 7 is grown, an example of which is shown in Ejaetroniosde by T. Mu-rotani et al.
Particularly in the latter case, the crystallographic orientation of the forming groove with respect to the crystal substrate should be set parallel to the (011) direction with respect to the (100) InP surface. by dovetail! If the entire (dovetail) groove is formed, growth within the groove is relatively easy and can be performed with good reproducibility.

However, it is difficult to create a dovetail-shaped groove width of approximately 2.0 μm or less with good reproducibility due to the following points.

(2) Normal photolithography is limited to a mask width of about 1.0 μm, and it is inevitable that the width of the grooves will be around 2.0 μm due to the etching during groove formation.

■Since the shape is doveta1/ (dovetail), the groove width becomes wider in the depth direction of the board.

Based on these facts, is it possible to create a device with good oscillation mode characteristics with a total active layer width of 2.0 μm or less? It was difficult to obtain.

On the other hand, if V@ is formed entirely instead of forming a dovetail groove, the above-mentioned drawbacks will be solved. In other words, ■The groove width becomes narrower in the depth direction from the crystal surface to 2.0 μm.
Active layer below? 〇 ■■Groove side surfaces are formed with low index surfaces, and because the etching speed is usually slow, there is almost no spread of the groove, and the cross-sectional shape of the groove can be completely controlled to form a single leg with good reproducibility. be able to.

■The V#l side surface becomes a flat surface, and when the entire active layer is formed within the groove, a layer with a uniform cross-sectional shape in the length direction of the groove is obtained, resulting in stable device characteristics. It is effective for

bottle Benefits such as:

However, when liquid phase epitaxial growth is performed on a substrate in which all V grooves are formed, there is a fatal drawback that the flange part is buried and it is difficult to obtain a flat crystal interface. By using the substrate on which the V-groove is formed, we take advantage of the advantages of V-groove formation, and form an epitaxial layer made of InGaAaP in contact with the upper end of the V-groove and spanning the upper end of the V-groove to create a flat crystal interface. The purpose is to obtain.

First, when a liquid-phase epitaxial layer is formed on a substrate on which a groove has been formed, the inside of the V-groove is filled with this epitaxial layer. 100) Epitaxial layer 7 made of InP on an InP substrate Ill having a surface
The case where #I+ is grown will be explained based on FIGS. 1 to 3.

First, a photoresist film having a groove is formed on an InP crystal substrate (1) having a (10G) ff plane using a photolithography method. IV@121 Prepare everything that was formed. At this time, the lnP etchant is usually Hat' (10
0% concentration) or Bi (5%)-methanol solution is used, and when Hcl (10096 concentration) is used, a1vStZ+[(221)] appears, and Br
(5%)-methanol solution is applied to Vh 7j fjii fCH2VI#t2+ surface with (111) A surface exposed. Next, as shown in Figure 2, V groove (
The InP epitaxial growth inside the V groove 121 formed at this time is epitaxially grown on the substrate (1) on which the InP groove (2j) is formed.
The surface grows parallel to the surface of the substrate 111, the flat surface (1a) of the 19 substrate il+, and 1n inside the groove (2).
The growth thickness dl of the P-type pitaxial growth layer (3) and the substrate (
Comparing the growth thickness d2Th of the InP epitaxial layer (4) formed on the flat surface (1a) in 1), the I
nP epitaxial growth) * The increase in the growth thickness dl of 131 is the growth thickness d of the summer nP epitaxial growth layer (4).
Although the epitaxial growth is relatively faster than the increase in V
#H2+ As the layer progresses to the top, the rate of increase in the growth thickness di of the InP epitaxial growth layer (3) becomes smaller than the rate of increase in the growth thickness d2 of the epitaxial growth layer (4). From this, as the growth of the InP epitaxial layer (31) progresses, the rate of increase in the growth thickness di of the IhP epitaxial layer (4) on the flat surface (la) of the substrate il+ l: The reason why the growth thickness dl is smaller than the growth thickness dl is thought to be as follows. There is, but there is a groove (
The solute from the liquid phase (P
) is diffused and the growth rate inside the V-groove (2) becomes relatively low when VC<<.

As mentioned above, when growing the upper part of V#1121, the increase rate of the growth thickness dl of the V groove (21 circular part) is
The term "increase in l" means that the more InP k epitaxially grows, the more the two InP fills.
The difference in level is huge! (That means that it is not possible to obtain an InP epitaxial layer with a flat surface of 1.)Based on this result, 1nP epitaxial & long 71+
The case of growing even thicker than 1ull+41 is shown in Figure 3.

As is clear from FIG. 3, the summer nP epitaxial growth 18131141μ remains uneven. In other words,
On the board 111i side VC, bVg12+upper end E (2a
) (2b) Upper Nikl, InP does not grow, ■ Groove (2
) Internal epitaxial growth layer (3) and flat surface (la)
Crack 15 between upper epitaxial growth M(4)]
It can be seen that the method of pressing the InP epitaxial layer 2 is not suitable because it remains as 161 and fills the inside of the V groove (2), leaving a flat surface.

Therefore, an InGaAsP x hytaxial growth layer is grown as an active layer in the V groove (21 circles) of the substrate +11,
When a 1nP pitaxial long layer is grown on top of it to fill the groove (21) to form a semiconductor laser, a crack (5) is created on the upper end (2a) (2b) of V mj121. (8) rarely occurs.

Fourth plan, this state? Figure 9 is a cross-sectional diagram of the semiconductor laser shown.
In Figure 1, 1nP formed with 111r[V quotient (2;
The crystal substrate (7) is the first 1nP epitaxial growth layer epitaxially grown on the bottom of the V#1121 of this substrate, and at the same time, a growth layer (81) is also formed on the flat surface (la) of the substrate (1). (91 is this ml of InP epitaxial growth layer (7) InGaAsP formed on soil
An active layer consisting of an epitaxially grown layer, in which an InGaAsP epitaxially grown layer (10) is simultaneously formed on the grown layer (8) 131141 rI substrate 1
The V-groove (2) of 1) is filled (in f7t), this active layer (8) and the IHGBA@F epitaxial growth layer (
lO) Second 1nP pitaxial growth layer formed in soil, +511611; 3: Upper end of the V groove 121 (2
m) (2b) % Tsumari■ Second InP epitaxial growth layer (3) formed in the groove (2) and second InP epitaxial growth layer (4) formed on the substrate ill-plane orientation (l&) As shown in FIG. The second In? formed on (la)? The epitaxial growth layer (growth cannot catch up to the 41 interface, and ψ at the optical surface of the substrate (1)
Since the InPUg is not long on the upper end fIS (2m) (2b) of the groove (2), cracks +51 +61 remain, making it impossible to obtain a flat surface and making it unsuitable for use as a semiconductor laser0 Inventors et al. As a result of further various studies, it was found that by epitaxially growing InGaAsP when filling the V-groove 121t in the InP substrate (1) on which the groove (2) was formed, ■ the upper end of the groove (2) ( 2B) It has been found that the occurrence of cracks in (2b) can be prevented and a flat surface can be obtained.

No. 5N is a cross-sectional view showing an embodiment of the present invention. In the figure, an InP crystal substrate (7) having 9 (100) planes is formed with the V groove (2) shown in FIG. 1 at il+. A first 1nP epitaxial growth layer is epitaxially grown on the bottom of the V-groove (2) of this substrate, and at the same time the substrate (1) is grown.
A growth layer (8) is also formed on the flat surface (1a).

O1)H To fill the V-groove (2; inner space) of the substrate 111, first InP epitaxial growth layer fil +8
1 and I formed on the upper part of the V groove (2) of the substrate full.
An epitaxially grown layer made of nGaABP,
11 V groove on the garment surface (2) Upper end '5 (2a) (2b)
IC contact, V m (upper end of 21 (2a) (2b)
It is formed across k. O2 is this 1nG
On the epitaxial growth hap consisting of aAsP [1n
This is the third InP epitaxial growth I- which was grown by Pi epitaxial growth.

In the structure configured in this way, the IfiGlAlP epitaxial growth layer θυ has a V-groove (
■Groove inside 21 (external to 21, that is, board (1)
It grows thicker than on the flat layer ff1(la).

■InGaA8P epitaxial growth layer (Ill H,
Substrate (11 V groove on second surface (21 upper end WI= (2a
) (2b) because growth takes place! As shown in Fig. 3 or uM4, cracks 15+161, which occur when the InP epitaxial layer 1B+141 is grown to fill the V-groove (21'), do not occur. I
nP Ebitaxyarno f1! The growth of (2) occurs over the entire surface at once, and unlike the case of the (100) surface with different steps as shown in Fig. 3 or 4, the growth of the third 1
nP pitaxial layer Qarl: Grows flatly.

Through these actions, it is possible to obtain crystals with a flat surface.

FIG. 6 is a cross-sectional view showing an embodiment of the present invention when applied to a semiconductor laser.
1 [81, the active layer (9), the 1iGaAIP epitaxial growth layer (IO), and the second InP epitaxial growth layer J31141 were formed, and then the In
The GaAsP epitaxial growth layer is in contact with the top end ff1s (2a) (2b) of the V groove (2) on the surface of the substrate 111, and the top end fl(i (2a) (2b) k
It is formed by straddling it. (c) is this In-
This is a third InP epitaxial growth layer formed on the GaAsP epitaxial growth layer Qll.

In a semiconductor laser configured in this way,

Similar to the one shown in FIG. 5 above, flat crystals of human blood can be obtained.

As stated above in this invention, the epitaxial layer of InGaAaP? ■On the surface of the substrate where the groove was formed, ■It was in contact with the upper end of the groove, and ■It was formed at the entire upper end of the groove.
By eliminating the difference in growth between the inside of the groove and the outside of the groove, that is, the flat surface of the substrate, it has the effect of making the entire surface completely smooth.
1

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the substrate fl' on which V#1121 is formed, Figs. 2 and 3 are cross-sectional views when the entire 1nP epitaxial growth layer is formed on the substrate (1), and Fig. 4 a. A cross-sectional view showing a semiconductor laser in the case where V#f121 of the substrate (1) is filled with a ¥r1nP epitaxial growth layer, FIG. 5 is a cross-sectional view of an embodiment of the present invention, and FIG. 6a
1 is a sectional view showing an entire example of a semiconductor laser according to an embodiment of the present invention. In the figure (1) is the substrate, 121t'IV groove, (2m)
(2b) Upper end of uV groove (2), αυU InGaA
It is an epitaxial layer consisting of an sP layer. Note that the same reference numerals in each figure indicate the same or similar parts. Agent Makoto Kuzuno - Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A semiconductor laser comprising: (1) a substrate made of InP with a groove formed therein; (2) an epitaxial layer made of InGBAgF formed across the top end of the groove, in contact with the upper end of V#l on the surface of the substrate;