JPH03151675A - End face radiation type semiconductor light emitting device and manufacture thereof - Google Patents

Abstract

PURPOSE:To solve problems of light emission efficiency, yield, and reliability, etc., being lowered by LPE(liquid phase epitaxial)-growth of an active layer for performing optical amplification on a striped mesa directly or through a predetermined LPE growth layer, isolated from parts other than the striped mesa. CONSTITUTION:A striped mesa part m is formed on the upper surface of an N-InP substrate 11 into an island shape, interrupted longitudinally of a device, on which substrate 11 there are grown four layers of an N-InP buffer layer 12, an InGaAsP active layer 13, a P-InP cladding layer 14, and a P-InGaAsP contact layer 15. The InGaAsP active layer 13 is grown such that its part on the upper part of the mesa part m is separated from other parts thereof, and about 2mum width thereof is buried in the P-InP cladding layer 14, whereby the so-called buried hetero structure is formed with the once LPE growth. Thus, since an end face radiation type LED of a window structure can be manufactured with the once LPE growth, there are eliminated problems on the manufacture which might be caused by lowering of light emission efficiency, yield, or reliability, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an edge-emitting semiconductor light emitting device suitable for use in optical communications and a method for manufacturing the same.

(Prior Art) Generally, an edge-emitting light emitting element (hereinafter referred to as an LED)
Compared to surface-emitting devices, the coupling efficiency to optical fibers is higher, and it is less susceptible to negative effects such as return light than lasers.
It is attracting attention for optical communications because it is easy to handle.

Edge-emitting LEDs emit light from the arm opening, but unlike lasers, it is necessary to take measures to prevent the arm opening from becoming a resonator in order to suppress laser oscillation. For this purpose, there is a method of etching and tilting the crack plane, or forming an excitation region and a non-excitation region of light in the stripe direction of the active layer, and absorbing the light returning to the excitation region into the active layer of the non-excitation region. Methods have been proposed to prevent this. In the so-called window structure, which has an excitation region with an active layer and a window region without an active layer, light is diffused radially from the edge of the active layer to the element end face or the open face of the arm. It is difficult for it to enter the
By combining the above two methods, the influence of reflected light can be almost completely eliminated.

An example of an edge-emitting LED having such a window structure is shown in FIG. Figures (a) and (b) are a cross-sectional structural view and a cross-sectional view taken along the line DD'. 71 is an N-InP substrate, 72 is an N-InP cladding layer, and 73 is InGaAs.
The P active layer 74 is a P-InP cladding layer, and the reference numeral 75 is a P-InGaAsP layer, which constitutes a so-called buried heterostructure, and the InGaAsP active layer 73 is removed from the middle to form a window region.

A P-InP buried layer 76 is formed in the removed region.

An N-InP current blocking layer 77 is buried to form a window region of the current non-injection region.

When the light generated in the InGaAsP active layer 73 in the excitation region is incident on the window region, it is not confined by the refractive index and spreads. Incident feedback is substantially prevented, whereby harmful laser oscillations are almost completely suppressed.

(Problems to be Solved by the Invention) As described above, edge-emitting LEDs with a window structure have extremely excellent characteristics, but the manufacturing process requires two or more liquid phase epitaxial (hereinafter referred to as LPE) growths. and has the following drawbacks:

That is, an etched double heterojunction (hereinafter abbreviated as DH), an N-InP cladding layer 72° InGaAs
P active layer 73. The P-InP cladding layer 74 is
When filling with PE growth, the interface is exposed to high temperature atmospheric gas, so the N-InP cladding layer 72 and the P-In
The PN junction formed by the P-embedded M2C is likely to deteriorate, causing an increase in leakage current and a decrease in luminous efficiency.

In addition, due to the temperature increase during the second LPE growth, impurities in the DH junction are diffused, and the PN junction position is, for example, N-In.
The P cladding layer 7 moves within 2 layers to reduce the luminous efficiency.

Furthermore, the two-time LPE growth process increases costs, and the long process reduces yield or reliability.

An object of the present invention is to eliminate the above-mentioned manufacturing problems of conventional edge-emitting LEDs due to deterioration in luminous efficiency, yield, reliability, etc.

(Means for Solving the Problems) The present invention achieves the above object by forming a striped mesa having a predetermined width extending in the light propagation direction on a predetermined first conductivity type semiconductor substrate. The active layer that performs optical amplification is partially excluded from the striped mesa and formed in a so-called island shape, and is separated from the part other than the striped mesa directly on the striped mesa or via a predetermined LPE growth layer. and LPE
In order to further improve luminous efficiency, current confinement in the mesa region is achieved by a current blocking layer, and in the longitudinal direction of the stripe, the active region on the mesa is used as an optical waveguide region and the other regions are non-guiding regions. The configuration is such that the partial waveguide structure serving as the wave region is formed at the same time.Furthermore, in order to facilitate their manufacture, the mesa structure is formed as a region sandwiched between two grooves, and the angle formed with the surface of the substrate is Hr. This is achieved by etching and smoothing with a methanol solution.

(Function) According to the present invention, since it is possible to manufacture an edge-emitting LED with a window structure by -degree LPE growth, the various problems described above caused by the conventional two-time LPI Σ growth can be solved. resolved.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention, and is a diagram (a).

Figure (b) is a cross-sectional structure diagram and a cross-sectional view taken along the line A-A', respectively, in which a striped mesa portion m is formed in the upper surface of the N-InP substrate 11 in the form of an island, discontinuous in the length direction of the element. The height is approximately 3.5 units and the width is 2.0 units. An N-InP buffer layer 1:l! is formed on such an N-InP substrate 11. , ■11GaAsP activity M13. P-InP
Four layers, cladding JP+14 and P-InGaAsP contact layer 15, were grown. When the shape of the mesa part m is controlled as described above, the InGaAsP active layer 13 grows with the two parts of the mesa part m cut off from the other parts as shown in the figure, and the size of the InGaAsP active layer 13 is about 2 pm. A wide InGaAsP active layer 13 was buried by a P--InP crat layer 14, and a so-called buried heterostructure was formed by one LPE growth. At this time, in the growth direction of the device, the figure (
As shown in b), the L n GaΔsP active layer 1: ( is interrupted, suppressing optical feedback due to reflection from the end facet between the folds, preventing laser oscillation, and increasing stability as an edge-emitting LED. Moreover, since the PN junction is not exposed to high-temperature gas for a long period of time, the conventional reliability degradation does not occur.

FIG. 2 is a diagram showing a second embodiment, in which FIG. 2(a) is a sectional view of a main part, and FIG. 2(b) is a sectional view taken along line BB'.

This differs from the first embodiment in that the N-
An N-InP buffer layer 22, an InP substrate 21''
Following the GaAsP active layer 23, a P-InP cladding layer 24 is grown in a mossy manner, and then an N-InP current blocking layer 25 is grown in a portion other than the mesa portion m, thereby increasing current efficiency. 1 to concentrate on the mesa part m
'iJ function, and even better characteristics than the first embodiment were realized.

Figure 3 shows the 33rd embodiment; Figure (a) and Figure (b).
) are the cross-sectional structure 1 and its sectional view taken along the line c-c'.

Generally, in order to effectively constrict a current, the layer between the current blocking layer and the active layer needs to have high resistivity and be thin, and a P-type layer is usually used for this layer. In the second embodiment described above, a total of six layers were grown, and it was necessary to precisely control the growth conditions for each layer.In the embodiment shown in FIG. 3, a P-InP substrate 31 was used instead of the conventional N-InP substrate. By adopting this method, the number of LPE growths is reduced and the process is simplified.

That is, on a P-I nP substrate 31 on which an island-shaped mesa portion m is formed, first, a NInP current flow layer 32 is formed in a region other than the mesa portion m, and then a P-InP buffer layer 33 + I is formed. nGaAsP active layer 3
4°N-InP cladding layer 35 and N-InGaAsP
An edge-emitting LED was created by growing four layers of contact layer 36.

Thus, when using a P-InP substrate, the number of LPE grown layers can be reduced from six to five. In this case, since ohmic contact to the N-type layer is easy, N-I
The electrode 38 can be easily formed on the N-InP cladding layer 35 without providing the nGaAsP contact layer 36, and furthermore, the number of LPE growth layers can be reduced.

One-time LPE of embedded heterostructure edge-emitting LED
The key point in creating the active layer by growth is to separate the active layer that amplifies light at the mesa portion, and to control the mesa portion to a predetermined height so as to allow LPE growth.

That is, in the third embodiment described above, in order to control the step difference after the growth of the P-InP buffer layer 33, the N-I
It is necessary to make the nP current cross layer 32 as thin as possible. However, in a normal mesa shape, in order to grow the N-InP current cross layer uniformly and without interruption beyond 32 m, the thickness must be
The inventors have found that it is necessary to make the thickness 0.7 μm or more. When the growth layer is thin, there is a break near the mesa part m because the growth rate is different between the flat part and the curved part, and because the curved part is faster, the solute that should originally grow in the flat part is eaten by the curved part. It's for a reason. Through precise experiments, the inventors found a solution to this phenomenon by forming a mesa part in a U-shaped groove, and found that no discontinuity occurs even when the thickness of the growth layer is 0.5 pn+ or less. did.

FIG. 4 is a sectional view of the main part of the fourth embodiment based on the above investigation results. First, on the surface of the P-InP substrate 41, a width of approximately 7 mm is applied.
Two grooves T each having a diameter of .mu.m and a depth of about 3.57 zm were formed in parallel with an interval of about 2p. On this substrate, NInP current block 9 layers 42 InP buffer layer 43° InGaAsP active layer 44 . Four N-InP cladding layers 45 were grown to form a device structure. As a result, the mesa portion m was formed in an island shape in the device length direction, and a stable edge-emitting LED in which laser operation was suppressed could be formed.

In order to obtain the optimal shape for the LPE grown layer, it is necessary to precisely control the degree of supersaturation of each layer, and to maintain the thickness of the LPE grown layer well even at the edges of the groove T, the method shown in Fig. 5 is required. As shown in the cross-sectional view, it is effective to further perform additional etching on the groove T after it has been formed to make the corners of the edge portion E smooth.

FIG. 6 is a process cross-sectional view showing the additional etching.
- A groove pattern is formed on an InP substrate 61 using a resist mask 62.
% solution etching to form grooves 63 (Figure (b)),
Next, the central mesa portion m is covered again with the resist mask 64 (Figure (C)) and etched with the Br methanol solution, so that the edge portion 65 on the outside of the groove 63 becomes appropriately smooth (Figure (D)). . This smoothness cannot be obtained with other etching solutions, such as H(I)-based solutions.

In the case of Br methanol, the optimum shape could be obtained most easily.

The edge-emitting LED shown in FIG. 5 has a current value of I f =
At 100 mA, the optical output P o = 1.5 mW and high efficiency 11-12- There is no instability of current confinement in the I)N thyristor structure even when the current value is increased, and the ambient temperature T
Even when the temperature was -60°C, the device operated stably without any laser movement.

Although the embodiments of the present invention have been described in detail using InGaAsP/InP-based materials, the present invention is also applicable to other materials such as Al
) Using a GaAs/GaAs-based compound semiconductor material,
Furthermore, by using an N-InP substrate instead of a P-InP substrate, an edge-emitting LED with high reliability, high efficiency, and low manufacturing cost can be realized.

(Effects of the Invention) As is clear from the above explanation, the present invention solves the problems of deterioration of luminous efficiency, yield, reliability, etc. and the problem of varnish 1-high in manufacturing, and can be formed by a single LPE growth layer. It is an edge-emitting LED with a window structure, and has the advantage of being able to be manufactured in a shorter time and more efficiently, so it can be implemented with great effects.

4. Brief Description of the Drawings FIG. 1 is a sectional view showing the first embodiment of the present invention, FIG. 2 is a sectional view showing the second embodiment, and FIG. 3 is a sectional view showing the third embodiment.
FIG. 4 is a sectional view showing an embodiment of the invention.

FIG. 5 is a sectional view of the main part of the fourth embodiment, FIG. 6 is a sectional view showing the process of forming the main part of the present invention, and FIG. 7 is a sectional view of a conventional example.

11, 21.71- N-I nP substrate, 12.22-
N-TnP buffer layer, 13.23.34°44 =-
InGaAsP active layer, 31.41-...P-InP substrate, 32.42- N-InP current current clock 9 layer 3.
43...P-InP buffer layer, 62.64...
Resist mask, 65°E...Edge part, m...
・Mesa part, 63°T...groove.

Claims (5)

[Claims] (1) On a semiconductor substrate of the first conductivity type, a striped mesa extending in the light propagation direction is partially removed to form an island mesa, and the island mesa is directly or predetermined. An edge-emitting semiconductor light emitting device characterized in that an active layer is epitaxially grown separated from other parts via an epitaxial growth layer. (2) A semiconductor layer of the second conductivity type is epitaxially grown following the active layer, and a semiconductor layer of the first conductivity type is formed on the active layer in a region other than the mesa. 2. The edge-emitting semiconductor light emitting device according to claim 1, wherein a partial waveguide structure is integrally formed in which the active region is a light waveguide region and the other region is a non-waveguide region. (3) On the semiconductor substrate of the first conductivity type on which the island mesa is formed, a first semiconductor layer of the second conductivity type is selectively formed other than on the mesa, and then a second semiconductor layer of the first conductivity type is formed. A semiconductor layer is grown at least in a region other than on the mesa, and then an active layer is grown to simultaneously constrict current to the mesa region and to transform the active region on the mesa into a light guiding region and the other non-guiding region. 2. The edge-emitting semiconductor light emitting device according to claim 1, wherein the partial waveguide structure serving as the wave region is integrally formed. (4) Claim (1) or claim characterized in that the mesa portion is formed on the semiconductor substrate in the form of two grooves sandwiched between them, and the corners that the grooves form with the semiconductor substrate are etched smoothly. The edge-emitting semiconductor light-emitting device according to item (3). (5) A striped mesa extending in the light propagation direction is partially removed on a semiconductor substrate of the first conductivity type to form an island mesa, and the striped mesa is formed directly on the island mesa or In the method for manufacturing an edge-emitting semiconductor light emitting device in which the active layer is epitaxially grown separated from other regions via a predetermined epitaxial growth layer, the striped mesa portion is formed into two
1. A method for manufacturing an edge-emitting semiconductor light-emitting device, which comprises forming an edge-emitting semiconductor light-emitting device in the form of a book sandwiched between grooves, and etching the corner portions of the grooves with a semiconductor substrate to smooth them using a Br methanol solution.