JPS6085584A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To improve reliability and service life by a method wherein a P-N junction is separated from an activation layer in a cleavage plane of a laser provided with a multilayer construction and a Fabry-Perot type resonator. CONSTITUTION:On an N type InP substrate 1, an InP buffer layer 2, non-dope InGaAsP activation layer 3, P type InP clad layer 4, P type InGaAsP electrode forming layer 5 are deposited, in that order. Next, impurity regions 200, 201 similar in conductivity type to the layer 4 are formed with a very small distance from the locations of cleavage planes 100, 101. In an element of this construction, with a P-N junction 300 being separated a very small distance from said layer 3, the progress of deterioration is decelerated by approximately a decimal place when aging is done under constant optical output conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser used as a light source in optical communications.

Semiconductor lasers continue to be improved in characteristics and reliability, and have a longer lifespan, and are now being put into practical use as light sources for optical fiber communications. However, recently, optical fiber communication systems are being introduced to submarine relay transmission, and semiconductor lasers are required to have even higher reliability and longer lifespan.

InGaAsP semiconductor lasers, which use InP as a substrate and have an emission wavelength that matches the low transmission loss wavelength range of optical fibers, have superior reliability and long life from the early stages of development compared to AtGaAs semiconductor lasers. It showed demand.

The first reason is that the propagation rate of threading dislocations from the crystal substrate due to current injection is extremely slow, and the second reason is that the optical damage at the arm opening is much lower than that of AtGa As. It was a small thing. The optical power density at which InGaAsP semiconductor lasers are optically damaged is several tens of MW/c.
yst. Therefore, in the case of InGaAsP semiconductor lasers, an end face protection film 2 is applied on the open surface, as in AtGaAs semiconductor lasers.

It has not been done.

However, when evaluating the inside of the device whose single-oscillation threshold current had increased by several tens of magnitude or more compared to when it was first used, a non-light-emitting portion was found in the active layer near the arm opening.

It has become clear that in order to achieve even higher reliability and longer service life, it is necessary to protect the interfold surfaces and to suppress their deterioration.

Conventional protection measures for inter-fold surfaces that achieve high reliability and long service life are At203 membrane and sio□ membrane.

The purpose was to form a Si3N4 film or the like on the interfold surface.

Since this protective means was applied to the opening surface of the arm after each element was folded, the manufacturing process was troublesome and the yield was low.

Therefore, an object of the present invention is to provide a semiconductor laser that has a good manufacturing yield, high reliability, and has a long life.

The structure of the present invention has a multilayer structure including a double heterojunction structure in which a first glue layer, an active layer, and a second cladding layer having a different conductivity type from the first cladding layer are sequentially laminated. A semiconductor laser including a Fabry-Bello resonator is characterized in that a small thickness range from an end face of the resonator that forms a reflective sharpness is the same conductive shadow region as the first or second cladding layer.

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention.
FIG. 1 is a perspective view of an AsP semiconductor laser. n-type InP substrate
An n-type InP buffer layer 2 (functionally a cladding layer and corresponding to the above-mentioned first adhesive layer 2) is formed on the n-type InP buffer layer 2 (functionally a cladding layer).

film thickness 1.5 μm), non-doped InGaAsP active layer 3
(Composition of 1.3μm in terms of emission wavelength, film thickness O9^5μm)
.

p-type InP cladding layer 4 (corresponds to the above-mentioned second cladding layer; film thickness 1.5 μm), p-type InGaAsP electrode forming layer 5
(Composition of 1.15 μm in terms of emission wavelength, film thickness of 0.8 μm)
After sequentially laminating the layers, a thickness of approximately 5 μm is placed deeper than the position where the interfold surfaces too and iot are formed (in the axial direction of the resonator).

A Zn selective diffusion region (an impurity region of the same p-type conductivity type as the cladding layer 4) 200, 201t with a depth of about 3 μm is formed, and an 8i02 oxide film stripe 3 with a width of about 10 μm is formed on the p side.
0. and Au-Zn type P thin metal bulb 40, A on the n side.
A device having the structure shown in FIG. 1 is obtained by mounting the u-Ge-Ni based n-side metal electrode 41 thereon.

The length of the resonator is 300 μm. The oscillation dark value of this device was 180 mA, and the differential quantum efficiency was 50%.

At the arm opening 100, the pn junction is a selective diffusion region 200 of Zn.
It is formed at the lower end (the hoe on the substrate l side) 300 of the In
It is separated from the GaAsP active layer 3. This shape is the same in the arm opening lot.

In the InGaAsP semiconductor laser, as mentioned above,
The optical output level is so high that optical damage occurs and the device instantly breaks down. However, when operating for a long time even at an optical output level of 5 mW or lomW, the electric field strength of the light is large in the active layer at the arm opening surface, resulting in concentration of 1-surface charge or increase in 1-surface rate density. Furthermore, it is thought that through a mechanism such as the formation of a deep level, a non-radiative recombination region is formed inside, gradually deteriorating the device characteristics. In this case, if a pn junction where the electric field strength is strongest is located in the active layer, as in most conventional semiconductor lasers, the progress of deterioration will be accelerated. In the device according to the first embodiment of the present invention shown in FIG.
Since it is approximately 0.5 pm away from the P active layer 3, S 5
It has been found that aging under the operating conditions of constant light output of 0° C.-5 mW can suppress the progress of deterioration to about one order of magnitude smaller than that of the conventional method.

Although the single oscillation threshold increased by about 5 mA by forming it in the Zn selective diffusion region 2001, the effect on device characteristics is small.

Figure 2 shows InGaAsP which is a second embodiment of the present invention.
FIG. 2 is a perspective view of an embedded semiconductor laser.

This structure is created by two rounds of liquid phase epitaxial (LPE) growth. In the first LPE growth.

An n-type InP buffer layer 2 (corresponding to the above-mentioned first cladding layer, film thickness 2.5μ) is formed on a (001)-faced InP substrate l.
m), a non-beef-InGaAsP active layer 3 (composition of 1.0 μm in terms of emission wavelength), and a p-type InP cladding layer 4 (corresponding to the above-mentioned second cladding layer; film thickness of 1 μm) are laminated. Next, parallel to the <110> direction.

Two grooves 21 and 22 with a depth of about 3 μm are formed with the mesa stripe 20 sandwiched between them. In the second LPE growth,
First, the p-type InP current blocking layer 6 (thickness 0.5 mm at the flat part).
5 μm), n-type InP current confinement layer 7 (thickness 0.5 μm in the flat part) is formed so as not to be laminated on the ffi straight stripe 20, and the p-type InP buried layer 8 is formed first.
(Film thickness 1.0 μm at flat part).

P-type InGaAsP electrode forming layer 5 (1.
A film having a composition of 15 μm and a film thickness of 0.5 μm at the flat portion is laminated over the entire surface.

Next, as in the case of the first embodiment, l opening surface 100° l
Approximately 5μm thick and approximately 5μm deep from the position where Ol is formed.
．． Selective Zn diffusion regions 200 and 201 with a thickness of 5 μm are formed. On the p side, there is an oxide film stripe 30.5io2 with a width of about 10 pm. An Au--Zn based p-side gold plate electrode 40 is formed thereon. On the n side, an Au-Ge-Ni gold maple electrode 4 is provided.
form 1. Finally, the resonator length is 300 μm and the second
Obtain the element shown in the figure.

In this embodiment, the one-oscillation threshold is 25 to 30 mA.

The differential quantum efficiency was 50 to 60 chi. In this structure as well, as in the first embodiment, a pn junction is formed at the lower end 300 of the Zn selective diffusion region 200 at the inter-fold plane loO, and a pn junction is formed at the lower end 300 of the Zn selective diffusion region 200. is seperated. This shape is also the same for the interfold surface 101. This element was tested in two-zinda tests under the operating conditions of constant light output of 50°C-5mW or 70°C-5mW, with Zn selective diffusion regions 200, 201
It shows about 1 inch of deterioration compared to elements that do not form shadows.

The increase rate of drive current under the condition of 70℃-5mW is 2, OX
It was a very small value of L OmA/hr.

FIG. 3 shows a third embodiment of the present invention.
FIG. 2 is a perspective view of an embedded semiconductor laser.

The difference from the second embodiment is that the Zn selective diffusion region 200
．． The width of the mesa stripe 201 is limited to 16 μm with the mesa stripe 20 as the center. Even in this case, since the pn junction is separated from the active layer 3 in the mesa stripe 20, the same effect as in the second example was obtained, and the deterioration rate was a small value as in the element of the second example. .

In the embodiment described above, the InGaAsP active layer 3 is.

Although the composition had an emission wavelength of 13 μm, similar results were obtained with compositions having emission wavelengths of 12 μm and 1.5 μm. In addition, although the example shows an InGaAsP system on an InP substrate, an AtGaAs system on a GaAs substrate,
Alternatively, a similar effect can be expected with InGaAs thread.

As explained above, one semiconductor laser of the present invention is as follows.

Since the position of the pn junction is separated from the active layer on the inter-fold surface, it is highly reliable and has a long lifespan.In addition, it is a method of applying diffusion to the growth wafer instead of the conventional method of applying an end face protection film on the inter-fold surface. Since the end face protection means is realized with this method, excellent effects such as high manufacturing yield and high productivity can be exhibited.

[Brief explanation of the drawing]

1 to 3 are perspective views showing first to third embodiments of the present invention, respectively. l...n-type InP substrate, 2...n-type I
nP buffer layer, 3...Randogue InGaAs
P active layer. 4...p-type InP cladding layer, 5...
p-type InGaAsP electrode forming layer, 6... p-type I
nP current blocking layer, 7... n-type InP current confinement layer, 890.11. . InP type buried layer, 20...Mesa stripe. 21.22... Two parallel grooves, 30...
...Oxide film stripe, 40...p-side metal electrode, 41...n-side metal electrode, too, tot...
. . . Example open surface, 200, 201 . . . Zn selective diffusion region, 300 . . . Lower end of diffusion region. Figure 3

Claims (1)

[Claims] A multilayer structure including a double heterojunction structure in which a first glue 2 Rad layer, an active layer, a 1st glue 2 Rad layer, and a second cladding layer of a different conductivity type are sequentially laminated, and a 7-applied bellows resonator. In a semiconductor laser comprising:
A semiconductor laser characterized in that the region has the same conductivity type as the glue 2 rad layer.