JPS5972788A - Embedded type semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain excellent characteristics of an element and to improve the manufacturing yield rate of the element, by providing an excellent P-N junction, which is formed by a semiconductor that surrounds an active layer light guide. CONSTITUTION:A wafer having a multilayer film structure, wherein the following layers are sequentially laminated on an N type InP substrate 1 having the surface direction of (001), is manufactured: an N type InP buffer layer 2 having the impurity concentration of 2X10<17>cm<-3>; an InGaAsP active layer 3 of a composition having the light emitting wavelength of 1.3mum; and a P type InP clad layer 4 in which Cd is used as impurities. Then, two grooves 90 and 91, which are in parallel with <110>, are formed, with a photoresist 80 as a mask. A mesa stripe 20 having the width of about 2mum is formed between the two grooves. After the photoresist 80 is removed, the second LPE growth is performed. Then, a P type current blocking layer 8 is laminated. Thereafter, N type InP current confining layer 9 is laminated on a flat part to the film thickness of about 0.5mum, but is not laminated on the upper part of the mesa stripe 20. Then, a P type InP embedded layer 10 is laminated on the flat part to the thickness of about 2mum including the upper part on the mesa stripe 20 so that the entire body is embedded and grown. Finally, a P type InGaAsP electrode forming layer 11 is laminated on the flat part to the film thickness of about 1mum.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried semiconductor laser in which leakage current flowing around an active layer is significantly reduced.

A buried semiconductor laser has a structure in which an active layer optical waveguide region with a width of about 2 μm is surrounded by a semiconductor layer with a large band gap energy and a small refractive index. It has excellent performance such as being capable of fundamental transverse mode oscillation and high-temperature CW operation.

In the fabrication of buried semiconductor lasers, in order to achieve high performance, it is important to efficiently concentrate the injection current in the narrow active layer optical waveguide region. In general, in a buried semiconductor laser, the rn junction formed in the active layer optical waveguide region is continuous with the rn junction formed in the surrounding semiconductor layer with large bandgap energy, and the diffusion potential between these two types of Pn junctions exists. Because of the difference in the current, the current flows concentratedly at the pn junction in the active layer optical waveguide region, causing radiative recombination. Therefore, if the .mu.n junction formed by the semiconductor layers surrounding the active layer optical waveguide region is good, current can be efficiently concentrated in the active layer optical waveguide region. However, this pn junction is generally formed by mesa etching to form a mesa stripe including the active layer optical waveguide region, and then buried and grown on the semiconductor layer exposed by the etching. It is formed by stacking semiconductor layers. This epitaxial layer interface is not necessarily good due to unevenness and dirt on the semiconductor surface exposed by mesa etching, or thermal damage to the crystal surface due to being held in a high temperature atmosphere before buried growth, and the interface state is likely to occur. Recombination of the injected carriers via this interface state causes a leakage current that flows around the active layer optical waveguide region, increasing the oscillation threshold of the buried semiconductor laser. The optical output tends to be saturated with an increase in the injection current, which has an adverse effect, and the yield of good products during device fabrication has been reduced.

Therefore, an object of the present invention is to provide a buried semiconductor laser which can obtain excellent device characteristics and improve the device manufacturing yield by improving the pn junction formed by the semiconductor surrounding the active layer optical waveguide. It is in.

According to the present invention, a mesa stripe is provided on a semiconductor substrate in which at least three layers of a buffer layer of a first conductivity type, an active layer, and a cladding layer of a second conductivity type are sequentially laminated, and a mesa stripe is provided on a semiconductor substrate, and a mesa stripe is provided on a semiconductor substrate, and a mesa stripe is provided in which at least three layers of a buffer layer of a first conductivity type, an active layer, and a cladding layer of a second conductivity type are laminated in sequence. In the buried semiconductor laser having a structure in which the mesa stripe is surrounded by a plurality of semiconductor layers including at least a buried semiconductor layer of the shape of 1) an n-junction formed by diffusing impurities into the buffer layer of the first conductivity type (or the buried semiconductor layer of the second conductivity type);
A buried semiconductor laser or the like is obtained, which is separated from the epitaxial growth interface between the buried semiconductor layer of the second conductivity type and the buffer layer of the first conductivity type.

Before explaining the examples, the basic concept of the present invention will be briefly explained. In order to improve the pn junction formed by the semiconductor layer surrounding the active layer optical waveguide region, the impurity concentration of the grown layer is compared during buried growth. By increasing the target height, impurities in the growth layer are diffused from the epitaxial growth interface from the solid phase to the same phase, and by forming the Pn junction away from the epitaxial growth interface, the interface quasi that tends to occur at the epitaxial growth interface is reduced. The aim is to minimize the negative effects of Such diffusion from the solid phase to the same phase is, for example, ■−
In group V compound semiconductors, this can be easily caused by using an impurity with a large diffusion coefficient such as Zn.

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

FIG. 1 shows a manufacturing method and a cross-sectional structural diagram of a buried semiconductor laser according to a first embodiment of the present invention.

FIG. 1(a) shows an n-type InP substrate 1 (with an impurity concentration of 2
x 10"cm-") on top of 2 x 101? α−
3 and a relatively low impurity concentration n-type InP buffer layer 2 (film thickness 3 μm) and InGaAsp+ active layer 3 (film thickness 0 .15 μm, non-doped), impurity concentration I using Cd as the P-type impurity
x 10”m-3 r-type InP cladding layer 4 (thickness 3
The p-type InGaAsP electrode formation layer 5 (
Film thickness: 0.6 μm.

This is a multilayer film structure wafer in which four layers with an impurity concentration of 2×10"tm-" are laminated. Next, as shown in Figure 1(b), use the normal photolithography method! 0<110
After forming a Sin film stripe 5o with a width of 5 μm parallel to the ) direction, mesa etching is performed using a Br-methanol etching solution to a depth of about 4 μm and reaching the n-type InP buffer layer to form an inverted triangular mesa. Form stripes 20. FIG. 1(c) is a cross-sectional view of a semiconductor laser device formed after the second LPE growth. In the second LPE growth process, St
First, a p-type InP current blocking layer 6 using Zn as a type 2 impurity is laminated to a thickness of about 1 μm while leaving the O2 film 50 intact. When the impurity concentration is increased to 2X 10"cm-", the KP-type InP current blocking layer 6 to Z
n-type InP buffer layer 2 with low impurity concentration and n diffusion
The surface of is inverted into a P shape.

Therefore, the InP pn junction 30 is formed at a distance of about 0.3 μm from the epitaxial growth interface 31. Next, n-type I
nP current confinement N13 (carrier m, degree 5 x 10
I7tnl-3) was layered in such a way that it was completely embedded. After the second LPE growth, the Sin film stripe 50 is peeled off.

The P-side type mirror 60 is formed by forming a 5i02 film 51 on the surface and then opening a window on the μ-type TnGaAsP electrode forming layer 5.
．． A Zn expansion layer 40 is formed at a depth of 5 μm, and after controlling the surface diffusion, an Au-Zn material is formed around it.

The n-side electrode 61 is formed using an Au-Ge-Ni based material.

In this structure, the InP layer is grown from the surface 3J of the n-type 1nP cladding layer 2, which is exposed to a high temperature atmosphere until the r-type InP current blocking layer 31 is laminated by LPE growth.
InP p connected to aAsP active layer optical waveguide region 301
N-junctions 30 are formed separately. 6L p-side electrode 60
When a forward bias voltage is applied with positive on the n-side electrode 61 and negative on the n-side electrode 61, the difference in diffusion potential between the Pn junction of InGaAsP and the rn junction 30 of InP in the InGaAsP active layer optical waveguide region 301 is as high as about 400 meV. , also InP?
111 of carriers via the interface state in the n-junction 30
Since there is no current path that would cause coupling, the injected current is efficient (concentrated in the InGaAsP active layer optical waveguide region 301).The oscillation threshold current value is as small as 15 to 20 m1 at room temperature, and The differential quantum efficiency also showed a high value of 60 to 70%.Also, when the resistivity is about 0.100 m, the film thickness of the InP current blocking layer is 1.
Because it is as thin as μm, the r-type InP cladding layer 4 is replaced with p-type InP.
The resistance to the current spreading to the current blocking layer 6 is high, and even if the bias voltage is further increased after oscillation, the current flowing through the InP Pn junction 30 hardly increases, so the optical output is pulse injection of about 500 mA or more. The current amount increased almost linearly, and a one-sided pulsed light output of 100 mW or more was obtained. It also has good temperature characteristics.
The characteristic temperature T0 expressed by hd-exp (π) is 75
The maximum CW humidity temperature when assembled on a diamond heat sink with the r-side electrode 60 facing downward was as high as 110°C. In addition, there was little variation in properties within the grown Ueno film, and a good yield of 70 pieces was obtained.

FIG. 2 shows a manufacturing method and a sectional view of a second embodiment of the present invention. In the first LPE growth process, as in the first embodiment, an n-type InP buffer layer 2 (film) with a low impurity concentration of 2 x 10"cm-" is formed on an n-type InP substrate 1 with a plane orientation of (001). thickness 3μm) and emission wavelength 1.3μm1lh
InGaAsP active layer 3 (film thickness 0.15 μm, non-doped), and P-type InGaAsP active layer 3 using Cd as an impurity.
P cladding layer 4 (impurity concentration I x 10"cm-"
, a film thickness of 1 μm) are sequentially laminated to produce a multilayer film structure. This is shown in FIG. 2 (&). Next, Figure 2 (b
), using the photoresist 80 as a mask, <
Two grooves 90 and 91 parallel to 110) are formed. The groove width is about 7 μm and the depth is about 2 μm. Two grooves 90.9
A mesa stripe 20 having a width of about 2 μm is formed between the stripes 1 and 1 . When etching and etching are performed using a Br-methanol solution using a photoresist mask, the etching and etching progress to the inside of the photoresist mask, so-called side etching. Therefore, the side surface of the mesa stripe 20 has a shape that gradually tapers upward. After removing the photoresist film 80, a second LPE growth is performed. FIG. 2(C) is a cross-sectional view of the device after LPE growth. First r form I
An nP current blocking layer 8 is laminated. If the thickness of the laminated film in the flat part is kept to about 0.5 μm, the layer will not be laminated on the upper part of the mesa near the central mesa stripe 20 because the growth on the side surfaces of the mesa is fast. In addition, the concentration of P-type impurity Zn was increased by 2×
If the value is set as high as 10I"cnT-", the surface of the n-type LnP buffer layer 20 is inverted to P-type as in the first embodiment, and the InP rn junction 30 is approximately 0.3 μm from the epitaxial growth interface 31. formed apart. Next, n-type In
P current confinement layer 9 (impurities: Te, lXl0"6n-
”) is laminated with a film thickness of about 0.5 μm on the flat portion, and is not laminated on the upper part of the mesa stripe 20.

Next, e-type InP buried layer 10 (impurity Zn, 7X1o
1"crn-3> is deposited to a thickness of about 2 μm on the flat part, thereby filling the entire area including the upper part of the mesa stripe 20. Finally, the P-type InGaAsP electrode forming layer 11 (at the emission wavelength 1.2 μm composition, impurity Zn
, an impurity concentration of 5×10"crn-") are deposited to a thickness of approximately 1 μm on the flat portion. InGaAsP is (0
01) Since the in-plane growth rate is fast, the concave part at the top of the mesa is completely filled in and the surface becomes flat. The r-side electrode 60 is made of Au.
- Zn-based electrode material, and Au-Ge-N for the n-side electrode 61.
T-type electrode material is used. The characteristics of the second embodiment are also the same as those of the InGaAgP active layer optical waveguide region 3 in the mesa stripe 20.
Since the InP pn junction 30 connected to 01 is away from the epitaxial growth interface 31, it is not affected by the adverse effects of interface states and the like. Also, since the flat part is a p-type junction, current will not flow unless a high voltage of about 10V is applied. Therefore, current flows in a concentrated manner in the area of the mesa stripe 20. The oscillation threshold is 10-20m1 and the differential quantum efficiency is 60
~70 yen, and a light output of 50 mW or more per side was obtained.

Characteristic temperature T. Excellent results were obtained with a maximum CW temperature of 70 to 90 and a maximum CW temperature of 130°C. The yield of good products is also good, about 8
The value became 0chi. Also, the structure is that there is an n-type I inside.
Since it has the nP current confinement layer 9, one side electrode 60
Since it is sufficient to form Zn on the entire surface, there is no need to selectively diffuse Zn as in the case of the first embodiment, and manufacturing is easy.

The present invention is not limited to the above two types of embodiments. For example, it is also possible to apply it to an A/xGa1-xAm type buried semiconductor laser.

Finally, to summarize the features of the present invention, by improving the p-n junction of the buried layer connected to the p-n junction of the active layer optical waveguide region, the degree of current concentration in the active layer optical waveguide region can be reduced. This is because a buried semiconductor laser with a low oscillation threshold, high differential Doji efficiency, and good temperature characteristics can be obtained in good yield.

[Brief explanation of the drawing]

FIGS. 1(a), (b), and (c) are the first embodiments of the present invention.
Manufacturing method and cross-sectional structure diagram of the example, FIG. 2(a),
(b) and (e) show the manufacturing method and cross-sectional structural diagram of the second embodiment of the present invention. In the figure, 1 is an n-type InP substrate, 2 is an n-type InP buffer layer,
3 is an InGaAsP active layer, 301 is an InGaAsP active layer optical waveguide j18 candy area, 4 is a door-shaped InP cladding layer, 5
and 11 are 1-type InGaAsP electrode formation layers, 6 and 8 are P-type InP@flow layers, and 7 and 9 are n-type I
nPjft flow confinement layer, 10 is an r-type InP buried layer, 20 is a mesa stripe, 30 is an InP layer junction, 31
is the epitaxial growth interface, 4o is the Zn diffusion region, 50
and 51 is a Sin film, 6o is an electrode on one side, 61 is an n-side electrode, 8o is a 7-hole resistor II, 9o and 91 are grooves. Representative patent attorney trip 0 0

Claims (1)

[Claims] 1. A multilayer mesa stripe is provided on a semiconductor substrate in which at least three layers, a buffer layer of a first conductivity type, an active layer, and a clad layer and a do layer of a second conductivity type, are laminated in sequence, and a second layer is laminated first.
In a buried semiconductor laser having a structure in which the mesa stripe is surrounded by a plurality of semiconductor layers including at least a buried semiconductor layer of a conductivity type, the buried semiconductor layer of the second conductivity type (or a buffer layer of a first conductivity type) A pn junction formed by diffusion of impurities into the first conductivity type B, F layer (or second conductivity type buried semiconductor layer) is connected to the second conductivity type buried semiconductor layer. A buried semiconductor laser, wherein the buried semiconductor laser is separated from an epitaxial growth interface of the buffer layer of the first conductivity type.