JPS62139377A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain the element which operates in a stable single mode with high yield by eliminating the need of connecting a negative resistance to an external part by arranging a distribution of resistance corresponding to a distribution of an electric field strength of the light in a direction of a resonator axis. CONSTITUTION:On a diffraction grating 60 formed on a surface of an N-type InP substrate 1, a lambda/4 shift region 50 of the boundary where a cycle of salients and recesses is inverted is formed. Next, on the substrate 1, an N-type InGaAsP light guiding layer 2, an InGaAsP active layer 3, a P-type InP cladding layer 4 and a P-type InP second cladding layer 5 are laminated by liquid-phase epitaxial growth. Then, an SiO2 film 110 is formed by CVD technique and this film 110 is removed into stripe form. Zn is diffused selectively down to the layer 5 to form a low resistance region 100. By using the substrate 1 from which the film 110 is removed, a P-type InGaAsP cap layer 9, an SiO2 insulating film 74, low reflection films 30 and 31, and a mesa stripe 70 are formed and the semiconductor laser element which operates by a stable single mode is fabricated with high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a 1" 14-body laser device used as a light source for communications, optical measuring instruments, etc.

(Problems that conventional technology and inventions are trying to resolve)
Distributed feedback type 'P4 body laser (Di
distributed Feedbaclc l, ase
r Diode; hereafter abbreviated as 1) lI″B LL)
, or distributed Bragg reflection type conductor laser (1) is
Tributed Bragg.

Reflector I, aser Diode;
DHRLD (hereinafter abbreviated as DHRLD) is expected to be used as a source for high-speed and long-distance original fiber communication, or as a light source for a primary metering sub-device with eight coherent optical systems due to its excellent single-wavelength operation, and rapid research and development is progressing. Enter.

By the way, DiI'BLD with a diffraction grating formed inside
However, not all of the fabricated devices exhibited stable single-axis mode operation, but depending on the phase of the diffraction grating at the end face of the device, it operated in a single-axis mode or in multiple-axis modes. I will do it. Also, DFB
When the operating current of the LD is increased to increase the optical output, a jump in the excavation axis mode may occur, causing a kink in the injection current-optical output characteristics. For the reasons mentioned above, there has been a problem in that it is difficult to obtain devices that operate in a stable single-axis mode with a high production yield. In order to solve the above problem, the present inventors invented a semiconductor laser having the structure shown in FIG. 3, which is described in Japanese Patent Application No. 125449/1982. This semiconductor laser responds to the electric field intensity distribution of light in the cavity direction.
In order to control the density of carriers injected into the active layer 3, the electrode fi-
The feature is that it is divided into three p-side electrodes 80, 81, and 82. When injecting current into this semiconductor laser device,
As shown in FIG. 4(a), each electrode 80, 81, 82
Load resistors with different resistance values outside of 100.101.10
2 was connected and used. By appropriately selecting the value of the load resistor used, this semiconductor laser device can control the electric field intensity of the light distributed in the cavity axis direction inside the semiconductor laser and the current 'IM degree, as shown in Figure 4(b). can form almost similar shapes. Furthermore, when the oscillation axis mode is different, the electric field intensity distribution of the light in that mode is different compared to the peak in FIG. Such an oscillation axis mode oscillation threshold becomes very large. Therefore, the axial mode with the electric field intensity distribution of light shown in Figure 4 (bl) oscillates stably.In fact, this semiconductor laser device has an element that operates in a stable single-axis mode up to a high output range of 50 mW or more. This was achieved with a high yield of about 70% or more. However, in the above semiconductor laser, the optimum load resistors 101 and 102.lQ3 had to be selected and connected to the outside of the semiconductor laser, which required a large amount of man-hours for assembly and adjustment. This has the problem that it requires a lot of man-hours.That is, the load resistance 100°101, 102 is p#Jt
Connect the lead wire 4L9 near the pole 80.81.82 Force 1
You need to take them out and connect them to each other. Conventionally, the lead wires for the semiconductor laser (electrode force) on the p-side and n-side electrodes were required to be one each, but now there are three or four lead wires, so a special mounting method for the semiconductor laser is required. is necessary,
Further, complicated assembly processes such as connection with load resistors 101, 102, and 103 are required.

Similar to conventional semiconductor lasers, the present invention has two
It is possible to obtain a device that has an electrode portion, has a high production yield, and operates in a stable single-axis mode. An object of the present invention is to provide a semiconductor laser and a method for manufacturing the same.

(Means for Solving the Problems) The semiconductor laser of the present invention has a structure in which a diffraction grating is formed adjacent to the active layer, and is approximately proportional to the electric field intensity distribution of light in the cavity axis direction within the active layer. means for controlling the injected current distribution shape into a shape, and the means is provided on a part of the cladding layer formed with the active layer sandwiched therebetween, and the resistor is distributed in the direction of the coronal axis. The structure is characterized by being made of semiconducting skin with a high density. The manufacturing method includes forming, on a semiconductor substrate of a first conductivity type, an active layer and a light guide layer which is adjacent to the active layer above or below and is a diffraction grating whose upper or lower surface has a periodic uneven shape. Further, a step of forming a cladding field composed of a low resistance layer, a high resistance layer and a high resistance layer of the cladding 1 on the laminated structure consisting of the active layer and the original guide layer; The structure is characterized in that it includes at least a step of forming a low resistance layer distributed in the axial direction of the resonator by diffusion or ion implantation to a depth that penetrates the high resistance layer and reaches the low resistance layer. ing.

(Operation) Before explaining the non-invention in detail, the basic idea of the present invention will be explained. In the previous invention, in order to control the current distribution in the resonator axis direction of the active layer of the semiconductor laser, the electrodes of the semiconductor laser were divided and a resistor of some force was connected to the outside of the semiconductor laser. In order to do this without dividing the electrodes, it is necessary to create a distribution in the resistance values of the current path from the m-pole to the active layer inside the semiconductor laser. In order to change the resistance value of the semiconductor layer, it is generally sufficient to change the carrier m degree. For example, the specific resistance A of p-type LnP skin has a carrier concentration of 1.
x When IQ “d”, approximately 0.10α, also 4×101
When it is reduced to 7cIIL', it becomes about 0.20a, which is twice as large. Therefore, by providing a carrier concentration distribution in the semiconductor layer in the current path leading to the active layer, the value of the 11L flow flowing into the active layer can be changed even if the electrodes on the surface of the semiconductor laser are the same. Therefore, it is possible to form a distribution in the current flowing to the active layer in accordance with the resonator axial electric field strength distribution inside the semiconductor laser. This will be explained below using examples.

(Example) FIG. 1 is a perspective view of a semiconductor laser showing an example of the present invention. This is a υFB LD in which a λ/4 shift region 50 in which the period of peaks and valleys of a diffraction grating 60 is inverted is formed in the center on an n-type 1nP substrate 1. This structure will be explained using the cross-sectional view of FIG. 2 showing the basic steps of the manufacturing process. First of all, Uko, whose surface is (001), reported in the proceedings of the 1981 National Conference of the Institute of Electronics and Communication Engineers, 1017. l) F″B
Similar to the LD, a λ/4 shift region 50 is formed at the boundary where the period of the peaks and valleys of the central diffraction grating is reversed. This diffraction grating 60 is formed using He-Cd with a wavelength of 321 nm.
This was done using a gas laser and interference exposure method. Diffraction grating 60
The period was 2000 and the depth was 800x. Next, by liquid phase epitaxial growth, an n-type InGaAsP original guide layer 2 (1.15 trys composition in terms of emission wavelength, pa
The thickness is 0.1 μBSn at the valley part of the diffraction grating ω.
, carrier concentration 7 × IQ"cm-"), non-doped 1nGaAsP fL layer 3 (1
．． 3μm composition, film thickness O11μ row p-type InP cladding layer 4
(pIiS thickness Q, 5 prn%Zfl do 1, carrier concentration 1 x IQ "crt*-") and p
- type 1nP second cladding Wji5 (film thickness Q, 5 μm,
Zn dose, carrier concentration 4 x IQ"cm-"
) are stacked. Next, (CVD on the surface as shown in Figure 0)
By S10! The film 110 is partially formed by forming the S i U x film 11Q using ordinary photolithography technology.
is removed in a stripe shape with a width of 100 μm perpendicular to the plane of the paper. Thereafter, Zn is selectively diffused to a depth of approximately 0.7 μm so as to penetrate through the 1nP second cladding layer 5 to form a low resistance region 1008. p-type InP second cladding layer 5
The carrier concentration of the low resistance region 100 is 3 x IQ''
It increases to "cry-".

The resistivity in this region decreased to about 0.04 QCm.

Next, the 5iQt film was removed by etching (d).
It is a diagram. From then on, as Mito et al. reported in Proceedings 857 of the 1985 National Conference of the Institute of Electronics and Communication Engineers.

This substrate is used to form a double channel brainer embedded structure shown in perspective view 1 of FIG. 1(a). p
The surface of the InGaAsP cap layer 8 is made of Cr/AL1 metal with a current confinement structure using a 5i (Jx) edge film. After polishing until smooth, %
An n-side electrode 83 was formed using n@AuGeNi metal. so that the low resistance region 100 is located approximately in the center.
After opening the valve to a resonator length of 300 μm, S
Low reflective film with a reflectance of about 2 cm by depositing an i-layer 30.31
was formed. The first factor (b) is a sectional view taken along the dashed line A-B-C in the perspective view of FIG. 1(a). This 1fru\i shows a cross section at the center of the mesa stripe 70, and shows the light emitting part of active pJ3. When a current was injected into the active layer 3 with the p-side electrode 86 biased positive and the n-side electrode 83 (-negative), a current of 20 m
A threshold (Oscillated at +1.

Almost the same optical output was obtained from the front and rear end surfaces (front and rear end surfaces), and the combined differential quantum efficiency of the light emitted from the front and rear end surfaces was 1i60%.

The oscillation spectrum is a single axis mode and its wavelength is 1.305
It was μm. No kink caused by axial mode jang was observed in the injection current-optical output, and the device operated in a stable single-axis mode up to a high output range of 40 mW or more.

Moreover, the number of devices exhibiting such stable 1-mode operation was about 70% or more of the total.

As described above, the reason why good device characteristics and a yield of 9 are obtained is considered as follows. Figure 1 (in bl, p
When the side electrode 867i-positive and the n1+III'g pole 83 are biased negatively and a current flows, the specific resistance of the low resistance region 100 in the p-1np second layer is approximately 0.
．． 040α or other areas have a specific resistance of approximately 0.2
Since it is uz, a difference in specific resistance of about 5 times occurs. Therefore,
The current flowing through the active N3 will produce a distribution similar to the shape shown by the broken line in Figure 4 (bl) in the direction of the collector.Therefore, the distribution of the photoelectric intensity and the electric density will change. They have similar shapes.If the injection flow is increased, an axial mode with the electric field intensity distribution shown by the real root in Fig. 4(b) is stably generated, and a different electric field intensity distribution is generated. The axis mode shown is less likely to oscillate. Therefore, the reproducibility and uniformity of the device operating in a stable single-axis mode have been improved.

In the embodiment shown in FIG. 1, the low resistance region 100 is provided in the center of the element, but for example, in FIG. When the size is increased to about 90%, the electric field strength distribution in the cavity direction inside the semiconductor laser increases toward the right end facet. In this case, it is necessary to provide the low resistance region 100 close to the right end face. Further, in the above embodiments, selective diffusion of Zn was used to form the low resistance region 100, but it can also be formed by ion implantation fF: such as f3e. In addition, in the embodiment, the cladding layer is composed of two layers, a low resistance layer and a high resistance layer, but it can also be made of other structures, such as a single low resistance layer, and an impurity compensation region is formed in the region near the output end face to increase the resistance. A resistance region distributed in the direction of the resonator may be formed.

Although the stripe structure is a buried stripe structure, the same effect as in the embodiment can be obtained with other stripe structures. (The striped structure is not an essential part of the invention).

(Effects of the invention) By providing a resistance distribution inside the semiconductor laser that corresponds to the electric field intensity distribution of light in the direction of the cavity axis, it was possible to obtain a device that operates in a stable single-axis mode at a high yield. .

Compared to conventional devices with divided electrodes, there is no need to connect a load resistor to the outside of the semiconductor laser, and the device can be used in the same way as a normal semiconductor laser.

[Brief explanation of drawings]

Fig. 1fa) is a perspective view of a semiconductor laser showing an embodiment of the present invention; (C) (d) is the first
Figure 3 is a perspective view of a conventional semiconductor laser; Figure 4 (a) is a schematic diagram of a conventional semiconductor laser connected to a load resistor;
Figure [b] shows the '44 layer degree distribution of light and the current density distribution inside the semi-integrated laser. Figure "F*l is n-type 1nP, d plate, 2 is n-type 1n (J a A
S P Former Kite/! 2. 3 rt l nGaAs
P 1.5-characteristic l-141dp type lnP Norad layer, 5
is p-type 1nf' current blocking layer, 8 is p-type InGaAS
Pary layer, 30.31 is low resistance IJgg, 50
λ/4 shift region, 60 is a diffraction grating, 7083H11
side electrode, 100 is low resistance region, 110 is 3102ψ
^ Mouth 1 Figure 2 Mouth 4th Figure Oz

Claims (1)

[Claims] 1. A multilayer laminated structure including at least an active layer and a diffraction grating formed adjacent to the active layer, and an electric field intensity distribution of light in the resonator axis direction within the active layer approximately means for controlling the injection current distribution shape into a proportional shape, the control means having a resistivity distributed in the axial direction of the resonator provided in a part of the cladding layer formed with the active layer sandwiched therebetween. A semiconductor laser characterized by comprising a semiconductor layer. 2. On a semiconductor substrate of a first conductivity type, an active layer and a light guide layer, which is adjacent to the active layer above or below and is a diffraction grating whose upper or lower surface has a periodic uneven shape, and a step of forming a cladding layer consisting of a low resistance layer and a high resistance layer on a laminated structure consisting of the active layer and the optical guide layer; A method for manufacturing a semiconductor laser, comprising at least the step of forming a low resistance layer distributed in the cavity axis direction by an injection method to a depth that penetrates the high resistance layer and reaches the low resistance layer.