JPS61102793A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To make it possible to obtain high output power, by using an etchant, which etches only a specified compound, performing selective etching, and forming a stripe shaped groove, whose shape is constant and bottom part is flat, on a semiconductor substrate. CONSTITUTION:On an n type InP substrate 9, an InGaAsP layer 10, a p type InP layer 11 and an n type InP layer 12 are sequentially grown. Then, a V shaped groove is formed from the surface of the n type InP layer 12. At this time, when a hydrochloric acid etchant is used, the InP is etched but the InGaAsP layer 10 is not etched. As a result, the flat V shaped stripe groove, whose bottom part comprises the InGaAsP layer 10 is formed so as to penetrate the p type InP layer 11 and the n type InP layer 12. When a sulfuric acid etchant is used, the InGaAsP layer 10 is etched but the InP layer 11 and 12 are not etched. Therefore, a groove penetrating the InGaAsP layer 10 is formed at the bottom of said groove. Thus the InP surface of the substrate 9 is exposed.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to a laser device using a compound semiconductor, and particularly to a semiconductor laser device having a structure in which an active layer is embedded in a stripe-shaped groove formed in a semiconductor substrate. and its manufacturing method.

<Conventional technology and problems> In order to obtain stable continuous oscillation with low current, an active layer is conventionally formed in a groove or mesa-like part formed on the surface of a semiconductor substrate, and energy is applied to the area around the active layer. Various semiconductor lasers have been proposed that have a structure (buried heterostructure) in which an optical waveguide is surrounded by a cladding layer with a large gap and a small refractive index. Fig. 3 is a cross-sectional view of a main part showing an example, in which 1 is an n-type 1nP substrate with a plane orientation (+00), 2 is a p-type 1nP layer, and 3 is a cladding layer made of n-type 1nP, which is buried in the trench. layer 3-a and layer 3-b deposited on p-type 1nP layer 2. 4 is an InGaAsP layer consisting of an active layer 4-a inside the trench and a layer 4-1 outside the trench. 5 is p-type 1
This is a cladding layer made of nP.

6 is a V-shaped groove formed in a stripe shape along the (Oll) direction. The active layer 4-a is embedded in the V-shaped groove 6, and the active layer 4-a formed of an InGaAsP layer is surrounded by an InP layer with a small refractive index and a large energy gear. It forms a leading wave path. Furthermore, most of the current injected from above and below is transferred to the active layer 4 because the p-type 1nP layer 2 and the n-type 1nP N 3 formed on both sides of the active layer 4-a act as reverse bias diodes. -a, high luminous efficiency can be obtained.

However, there are two major problems with such a buried semiconductor laser element. The first is InGaAsP
Active layer 4-a and InP cladding layer 3- surrounding it
Since there is a large difference in refractive index between the active layer 4-a and the active layer 4-a, it is necessary to precisely manufacture the active layer 4-a with a narrow dimension of 2 microns or less in width. The second is the active layer 4- of the injected current.
The proportion of current flowing through parts other than a increases as the injection current increases. This is the n-type 1nP layer 3
-b.

Since the p-type In'P layer 2 and the n-type 1nP substrate 1 are equivalent to an n-p-n transistor, the increase in injection current causes
p which plays the role of the base of the above transistor structure
This is considered to be because the current 8-a injected into the InP type layer 2 increases, and the current 8 flowing through regions other than the active layer 4-a increases due to the current amplification effect of the transistor. This effect can be realized by reversing the p-type and n-type of each semiconductor layer, and the above transistor structure becomes a p-roll type, and its current amplification factor is smaller than that of an n-p-n type transistor. It is thought that it is possible to reduce the amount by that amount. However, from a practical point of view, it goes without saying that it is desirable to be able to obtain good characteristics with either polarity. Current 8 flowing through a region other than the active layer 4-a
The relative increase in current 7 flowing through the active layer 4-a causes problems such as a decrease in luminous efficiency and a difficulty in obtaining high output.

<Object of the Invention> The present invention has been made to improve the two major drawbacks of the conventional buried heterostructure semiconductor laser device as described above, and it is possible to easily fabricate the active layer and ensure reproducibility. It is an object of the present invention to provide a semiconductor laser device in which an increase in reactive current flowing in areas other than the active layer is suppressed.

<Structure of the Invention> A feature of the present invention is that, for example, by selectively etching a compound semiconductor using an etchant that etches only a specific compound, a flat stripe shape with a uniform bottom is formed on a semiconductor substrate. A groove is formed, an active layer is layered at the bottom of the groove, and the active layer is sandwiched in the horizontal direction by a cladding layer having a lower refractive index and a larger energy gap than the cladding layer, and further has a larger energy gap than the cladding layer. The cladding layer is sandwiched from above and below to create an embedded structure.

<Example> An example of the present invention will be described with reference to FIGS. 1 and 2. 1(A) CB)(C)G)) are schematic explanatory diagrams showing the manufacturing process of the semiconductor laser device of this example. first,
As shown in FIG. 1, an InGaAsP layer 10 is formed on an n-type 1nP substrate 9 by epitaxial growth. p-type 1nP layer 1
1. The n-type 1nP layer 12 is sequentially grown into multiple layers. A photoresist mask is made on top of this, and a V-shaped groove is formed from the surface of the n-type InP layer 12 using a normal photolithography technique.

At this time, as an etchant, a hydrochloric acid-based etchant, such as HC
If a solution with a volume ratio of I and H2O of 4:1 is used, lnP
is etched, but the InGaAsP layer 10 is not etched. As a result, as shown in FIG. 1 (CB), a flat V-shaped stripe groove whose bottom portion is made of the InGaAsP layer 10 is formed passing through the p-type 1nP layer 11 and the n-type InpH layer 12. Next, use a sulfuric acid-based etchant, such as H2S.
If a volume ratio of O4, H2O2 and H2O of 3:1:1 is used, the InGaAsP layer IO will be etched, but the InP layers I+ and +2 will not be etched, as shown in FIG.
An InGaAsP layer 10 is placed at the bottom of the groove as shown in C1.
A groove passing through the substrate 9 is formed, and the InP surface of the substrate 9 is exposed.

Here, using the Evita kinial growth technique again, first, the second InGaAsP layer 13-a, l 3-1) is grown by the above I
Grow it on the exposed surface of the substrate 9 in the groove and on the n-type 1nP layer 12 to a thickness comparable to or less than that of the nGaAsP layer 10,
After that, a p-type 1nP cladding layer 14 is grown thickly so as to overlap the InGaAsP layer of the cylinder 2, and the Songzi structure shown in FIG. 1 (2) is exploded. Newly grown 1nGaAsP in the trench
The I column 13-a becomes the active layer.

In the semiconductor laser device of 71, 7 structure, InGaA
By appropriately selecting the composition (mixed crystal ratio), the sP layer 10 can be made into a layer having a lower refractive index and a larger energy gap than the GaAsP active 1ffl13-a. In addition, the refractive index of the InGaAsP layer 10 is closer to that of the active layer 13-a than that of InP in any composition, so even if the width of the active layer 13-a is made wider than that of the buried laser device shown in FIG. -Transverse mode oscillation can be achieved. An n (1g electrode) is formed on the substrate 9, and a p-side electrode is formed on the cladding layer 14 directly or after depositing a cap layer for ohmic contact by vapor deposition, etc., and a driving current is injected through both electrodes to form an active layer. Laser oscillation is started at 13-a.

FIG. 2 is a schematic diagram showing a cross section of a main part of the semiconductor laser device of this example and the flow of an injected current. InGaAsP layer 10
are the upper and lower InP layers 9, 1 for all compositions.
Since the energy gap is smaller than 1, its thickness is set to 0.
．． If it is made sufficiently thin to about 1 micron, it becomes an n-type 1nP layer 9.
．． p-type 1nP layer 11. n composed of n-type 1nP layer 12
−p−n) The '+u Ml gain of the transistor can be lowered. Therefore, even if the injected current is increased, most of the current flows through the active layer 13-a as shown by arrow 15, and the current that does not flow through the active layer 13-a as shown by arrow I6 is suppressed to a small amount. This makes it possible to reduce the drop in luminous efficiency when the injection current is increased compared to a conventional buried heterostructure semiconductor laser device. InGaAsP
Even when the layer 10 is thinly deposited on the substrate 9, striped grooves can be reliably formed by the selective etching method, and since the substrate 9 is not etched, the bottom of the groove can be left flat. . Therefore, the active layer 13-a can be formed within the groove penetrating the 1pGaAsP layer 10 with ease and good reproducibility.

In the above embodiment, the case of InP-InGaAsP was described, but the present invention is also possible with a combination of compound semiconductors.

(Effects of the Invention) As detailed above, the semiconductor laser device of the present invention has a small decrease in luminous efficiency even when the injection current is increased, and can achieve high output.Moreover, single-transverse mode oscillation can be achieved. It is also easy to manufacture.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the manufacturing process of a semiconductor laser device showing one embodiment of the present invention. FIG. 2 is a schematic diagram showing the main part configuration of the semiconductor laser device shown in FIG. 1 and the flow of injection current. FIG. 3 is a schematic diagram showing the main part configuration of a conventional buried semiconductor laser and the flow of injection current.

Claims (1)

[Scope of Claims] 1. In a buried semiconductor laser device in which the active layer is surrounded in the vertical and horizontal directions by a heterojunction interface, a first semiconductor laser having a smaller refractive index and a larger energy gap than the active layer in the horizontal direction of the active layer A semiconductor laser device characterized in that the active layer and the first layer are surrounded in a vertical direction by a second layer having a smaller refractive index and a larger energy gap than both of these layers. 2. The first I epitaxially grown on the InP substrate
Claim 1: The nGaAsP layer is removed by etching in a stripe pattern, and a second InGaAsP layer having a higher refractive index and a smaller energy gap than the first InGaAsP layer is buried in the etched away portion to form an active layer. The semiconductor laser device described above. 3. The second InGaAsP layer is deposited on the first InGaAsP layer and the second InGaAsP layer.
3. The semiconductor laser device according to claim 2, wherein the AsP layer is sandwiched between InP in the vertical direction.