JPH04142789A - Semiconductor light-emitting element - Google Patents

Abstract

PURPOSE:To enable a semiconductor light-emitting element to be easily controlled in a manufacturing process and improved in performance by a method wherein a first conductivity type semiconductor substrate and a first conductivity type second semiconductor layer are electrically connected together. CONSTITUTION:An N-type InP block layer 2, a P-type InP buffer layer 3, an InGaAsP active layer 4, and an N-type InP clad layer 5 are laminated through a first epitaxial growth on a P-type InP substrate 1 on which a mesa stripe 10 has been formed. The InGaAsP active layer 4 and the N-type InP clad layer 5 are selectively removed, and an N-type InP buried layer 6 is made to grow through a second epitaxial growth. A current is effectively injected into an oscillation region 10 from the mesa stripe 9 of the P-type InP substrate 1 passing through the P-type InP buffer layer 3. A current blocking region 11 is made to serve as a thyristor of a PNPQN structure which contains the InGaAsP active layer 4. Therefore, it is high in ON-state voltage and can be kept in an OFF-state at a high temperature operation or at a high output operation, so that a semiconductor light emitting element can be kept high in oscillation efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to semiconductor light-emitting devices such as long-wavelength solid conductor lasers used in optical fiber communications and the like.

A conventional semiconductor laser is usually manufactured by forming a double heterojunction including an active layer by a first epitaxial growth, defining an oscillation region by ζ stripe etching, and then burying the stripe by a second epitaxial growth. At this time, a thyristor with a PNPN structure is formed in a region other than the oscillation region, which becomes a current blocking region. As long as this thyristor remains in the OFF state, current is concentrated in the oscillation region and good oscillation efficiency is maintained. Therefore, increasing the ON voltage of the thyristor improves the performance of the laser.Especially during high temperature operation or high output operation, the voltage applied to the laser increases, creating a thyristor risk with a high ON voltage. This method is described in the IEEE Journal of Lightwave Technology (IEEE JOU).
RNAL OF LIGHTWAVE TECHNOLO
GY ) Vol. LT-2 No. 4 (August 1984) No. 49
As described on page 6, the structure of the SIRISK is PNPQN (Q is a quaternary layer), and by inserting a Q layer with a small forbidden band width, the electron injection efficiency is reduced and O
There is a way to increase the N voltage. An example of a conventional semiconductor light emitting device using this structure is shown in FIG. This is published in IEE Journal of Lightwave Technology Vol. 1 No. 1 (March 1983, No. 9).
As described on page 95, it is called the DC-PBH type and has good characteristics such as high output and high temperature operation.

A conventional semiconductor light emitting device will be explained below.

FIG. 4 is a sectional view of a main part of a conventional semiconductor light emitting device. As shown in the figure, the conventional semiconductor light emitting device has an N-type InPz< buffer layer 52 . Indium gallium arsenide phosphide (InGaAsP)
Active layer 53. P-type 1nP cladding layer 54. P-type Ir1P
Block layer 55. N-type InP block layer 56. P-type In
P buried layer 57, P type InGaAsP cap layer 58
is formed, and has a groove 59 for forming a mesa stripe in a part. 60 is the upper part of the stripe, 61
is the oscillation region.

In this way, the trench 59 includes the InGaAsP active layer 53.
From the N-type InP block layer 56 on the outside of the
Five layers up to the nP buffer layer 52 form a thyristor with a PNPQN structure, and the ON voltage of the current blocking region can be increased. Therefore, an effective current is injected into the oscillation region 61 even during high output operation, and good oscillation efficiency is maintained.

Problems to be Solved by the Invention However, although the conventional DC-PBH type laser described above has excellent characteristics, it has the following problems in the manufacturing process.

In the DC-PBH type laser, in order to form a thyristor with a PNPQN structure, a P-type InP block layer 55 and an N-type InP block layer 56 are formed in the second epitaxial growth.
and P-type InP buried layer 57 and P-type 1 nGaAs P
The first cab layer 58 is grown, but at this time the P-type 1nP block layer 55 and the N-type InP block layer 56 are not grown on the upper part of the stripe 60. This strictly controls the degree of supersaturation in the melt solution, eliminates the degree of supersaturation in the upper part of the stripe 60 by utilizing the region where the growth rate is high in the step part of the groove 59, and prevents crystal growth in the upper part of the stripe 60. ing. However, if the degree of supersaturation changes slightly or if the shape of the stepped portion of the groove 59 differs slightly, the upper part 60 of the stripe may grow with a slight degree of supersaturation. Furthermore, even when no crystal grows in the upper part 6o of the stripe, the degree of supersaturation is slightly small (as a result, the N-type InP block layer 56 is interrupted at the shoulder part of the groove 59.
H-type lasers have problems in that it is difficult to form them with good reproducibility due to structural problems, and the yield is low and productivity is poor.

The present invention solves the above-mentioned conventional problems, and aims to provide a semiconductor light-emitting device that can be easily controlled in the manufacturing process and has good performance as a manufactured device.

Means for Solving the Problems To achieve this object, the semiconductor light emitting device of the present invention includes:
A first semiconductor layer of a second conductivity type, a second semiconductor layer of the first conductivity type, and an active layer are formed on a semiconductor substrate of a first conductivity type on which a mesa stripe with a predetermined width and height is formed. The third
, a fourth semiconductor layer of the second conductivity type are sequentially formed, the third semiconductor layer and the fourth semiconductor layer are selectively removed, and a fifth semiconductor layer of the second conductivity type is formed. It has a formed configuration.

At this time, the first semiconductor layer is grown except for the upper part of the mesa stripe, or the conductivity type of the region of the first semiconductor layer grown on the upper part of the mesa stripe is partially inverted,
By setting the semiconductor substrate to the first conductivity type, the semiconductor substrate of the first conductivity type and the second semiconductor layer of the first conductivity type are electrically connected to each other.

This configuration allows PNPs to be processed without strict supersaturation control.
Since it is possible to form a current blocking layer having a QN structure thyristor, it is possible to solve the manufacturing problems that have arisen with the conventional DC-PBH type.

Example Regarding a semiconductor light emitting device according to an example of the present invention.
A GaAsP/InP laser will be explained as an example. 1st
The figure is a sectional view of a semiconductor light emitting device according to an embodiment of the present invention. On the P-type InP substrate 1 on which the mesa stripe 10 is formed, an N-type 1n layer is formed by first epitaxial growth.
P block layer 2, P-type InP buffer layer 3, and InGaA
The sP active layer 4 and the N-type InP cladding layer 5 are laminated to form an InP active layer 4 and an N-type InP cladding layer 5.
The GaAsP active layer 4 and N-type InP cladding layer 5 are selectively removed, and N-type InP is grown by second epitaxial growth.
A buried layer 6 is grown. 7 is the N side electrode, 8 is the P
This is the side electrode. The current flows from the mesa stripe 9 of the P-type InP substrate 1 through the P-type InP buffer layer 3 to the oscillation region 10.
effectively injected into the Current blocking region 11 is made of InGaAs
Since the thyristor has a PNPQN structure including the P active layer 4, the ON voltage is high and the OFF state can be maintained even during high temperature operation or high output operation, and high oscillation efficiency can be maintained.

Next, the first manufacturing process of the laser of the present invention will be explained.

FIGS. 2(a) to 2(C) are cross-sectional views of the manufacturing process of a semiconductor light emitting device in one embodiment of the present invention. As shown in FIG. 2A, mesa stripes 9 are formed on a P-type InP substrate 1 by ordinary photolithography and etching steps. The width and height of mesa stripe 9 are approximately 2
μm and approximately 0.7 μm. Next, as shown in the same figure (b), the N-type 1nP block layer 2, the P-type 1nP buffer layer 3 and the InGaAsP are formed by first liquid phase epitaxial growth.
An active layer 4 and an N-type 1nP cladding layer 5 are laminated. At this time, the N-type 1nP block layer 2 is selectively grown except on the mesa stripe 9. This can be easily done using a two-phase melt method. The two-phase melt method is I
By putting an excessive amount of nP crystal into the melt solution, the degree of supersaturation of the solution can be stably suppressed to a low level, so that the degree of supersaturation disappears and the crystal does not grow at the top of a step such as the mesa stripe 9. This can be carried out much more easily than in the DC-PBH type, which requires growth while strictly controlling the degree of supersaturation. The thickness of each layer is 0.7 μm for the N-type InP block layer 2 and 0.7 μm for the P block layer 2 from the substrate side.
InP type buffer layer 3: 0.5 μm, InGaAsP active layer 4: 0.1 μm, N type rnP cladding layer 5: 0.7 μm.
It was set as μm. Next, as shown in the same figure (e), the InGaA
The sP active layer 4 and the N-type InP cladding layer 5 are selectively removed. This is used for selective etching of InP with hydrochloric acid (HC).
i! ) can be easily carried out by using sulfuric acid (H2S04):hydrogen peroxide (H202) as selective etching of InGaAsP.

Next, N-type InP is grown by second liquid phase epitaxial growth.
After growing the buried layer 6, two electrodes 8 and NfIII are grown.
An electrode 7 is formed to form a laser. The feature of the laser manufacturing process described above is that the N-type InP block layer 2 can be grown using a two-phase melt method. This eliminates the need to strictly control the degree of supersaturation of the solution, making it possible to manufacture lasers with very good reproducibility.

Next, the second manufacturing process of the laser of the present invention will be explained. FIG. 3(a) is a diagram for explaining the second manufacturing step, and FIG. 3(b) is an enlarged view of the main part of FIG. 3(a). First, as in the first manufacturing step, P
Mesa stripes 9 are formed on a type 1nP substrate 1 by ordinary photolithography and etching processes. Next, as shown in FIG. 3(a), an N-type InP block layer 21, a P-type InP buffer layer 22, an InGaAsP active layer 23, and an N-type InP cladding layer 24 are laminated by first liquid phase epitaxial growth. However, the difference from the first manufacturing process is that the first N-type rnP block layer 21
is also grown on top of mesa stripe 9.

If the thickness of the N-type 1nP block layer 21 is 1 μm, it grows on the mesa stripe 9 by about 0.3 μm. In the case of InP, zinc (Zn) is usually used as a P-type dopant, but since Zn has a large diffusion coefficient, it diffuses into the N-type layer during growth. This situation is shown in FIG. 3(b). This is an enlarged view of the upper mesa stripe 25 in FIG. 3(a).
A state in which Zn is diffused from the buffer layer 22 to the N-type 1nP block layer 21 is shown. The part where Zn diffuses from the P-type 1nP substrate 1 to the N-type InP block layer 21 and is inverted to P-type is the inversion region 26, and the P-type InP buffer layer 22
The inversion region 27 is a portion where Zn is diffused from the N-type InP block layer 21 and inverted to P-type. This reversal area 26
．． The depth of 27 is determined by the difference in carrier concentration between P-type and N-type. The carrier concentration of the P-type InP substrate 1 is approximately three times that of the N-type 1nP block layer 21, and the carrier concentration of the P-type I
When the carrier concentration of the nP buffer layer 22 is about 1.5 times, the depth of the inversion region, that is, the widths of the inversion region 26 and the inversion region 27 are about 0.2 μm and about 0.1 μm, respectively. Therefore, as shown in FIG. 3(b), the inversion region 26 and the inversion region 27 are connected above the mesa stripe 9, making it possible to electrically conduct the P-type InP substrate 1 and the P-type InP buffer layer 22. The subsequent steps are exactly the same as the first manufacturing step. The features of this second manufacturing process are:
The advantage is that the N-type InP block layer 21 can also be grown on the mesa stripe 9.

This eliminates the need to strictly control the degree of supersaturation of the solution, making it possible to manufacture lasers with very good reproducibility and improving yield.

Next, the characteristics of the laser of the present invention manufactured in this way will be explained. The oscillation threshold was approximately 15 mA, and an external differential quantum efficiency of approximately 25% was obtained. Further, a maximum optical output of 5 QmW and a maximum oscillation temperature of 120° C. were obtained. The reason why such high output and high temperature operation was achieved is that the PNPQN thyristor in the current blocking region 11 shown in FIG. 1 is working effectively.

In this example, the InGaAsP active layer P system was explained, but other compound semiconductor materials (for example, A2GaA
s/GaAs system) may also be used.

Effects of the Invention As described above, the present invention can realize an excellent semiconductor light emitting device in which a current blocking layer of a PNPQN structure can be formed without strictly controlling the degree of supersaturation of a solution in its manufacturing process.

Further, in the structure of the present invention, only one layer is required for the second epitaxial growth, and it is also possible to simultaneously grow semiconductor layers on a plurality of substrates.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts of a semiconductor light emitting device according to an embodiment of the present invention, FIGS. 2(a) to (C) are sectional views of the manufacturing process of the same semiconductor light emitting device, and FIG. FIG. 3(b) is an enlarged view of the main part of FIG. 3(a), and FIG. 4 is a sectional view of the main part of a conventional semiconductor light emitting device. 1...P-type 1nP substrate (semiconductor substrate), 2...
...N-type InP block layer (first semiconductor layer), 3
...P-type 1nP buffer layer (second semiconductor layer)
, 4... InGaAsP active layer (third semiconductor layer), 5... N-type InP cladding layer (fourth semiconductor layer), 6... N-type layer nP Buried layer (fifth semiconductor layer)

Claims (1)

[Scope of Claims] (1) On a semiconductor substrate of a first conductivity type on which mesa stripes of a predetermined width and height are formed, a first semiconductor layer of a second conductivity type; A second semiconductor layer, a third semiconductor layer serving as an active layer, and a fourth semiconductor layer of the second conductivity type are sequentially formed, and the third semiconductor layer and the fourth semiconductor layer are selectively formed. A semiconductor light emitting device in which a fifth semiconductor layer of a second conductivity type is formed. (2) The semiconductor light emitting device according to claim 1, wherein the first semiconductor layer is formed except for the upper part of the mesa stripe. (3) The semiconductor light emitting device according to claim 1, wherein a portion of the first semiconductor layer formed on the mesa stripe is inverted to the first conductivity type.