JPH03120886A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To realize current constriction with good reproducibility and to enable stable basic transverse mode oscillation and low threshold current oscillation by irradiating ion beam having a uniform direction to dry-etch a contact layer of a gain waveguide region. CONSTITUTION:A lamination wafer is etched to a middle of a second clad layer 105 to a shape of a rib etching mask 107 to form a rib. A single crystal ZnSXSe1-X layer 109 is formed on a second clad layer in the outside of the rib. A single crystal ZnSXSe1-X layer 110 is formed on a rib-etching mask 107 above the rib. Polycrystal ZnSXSe1-X layer above the rib is selectively etched and removed. Then, a p-type contact layer 106 is etched and removed to remain in stripe and a part of a gain waveguide part is exposed. The exposed contact layer is removed by reactive ion etching using chlorine. SiO2, Si3N4 or Al2O3 is used as a dielectric.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor laser that oscillates at a low threshold current (hereinafter referred to as 1th) and has low noise and high output characteristics. .

[Prior Art] When a semiconductor laser (hereinafter referred to as LD) is used as a light source for an optical information processing device, etc., a part of the emitted light is reflected by an external optical system and returns to the resonator of the LD. Due to the interference effect, the noise component of the output light from the LD (
(hereinafter referred to as return optical noise) increases, which poses a practical problem. As a means of reducing this return optical noise, there is a method of multiple oscillation of longitudinal modes. As a way to achieve this,
There is an LD having a structure as shown in FIG. On an n-type GaAs substrate 701, an n-type GaAs buffer layer 702 and an n-type A
lGaAs first craft layer 703, active layer 704, p
type AlGaAs second cladding layer 705, p-type GaAs
After the contact layers 706 are sequentially stacked, the second cladding layer is etched away halfway to form a rib-shaped optical waveguide. Next, Zn5e, which is an n-vr compound semiconductor
The layer 707 is buried, a striped current injection region is formed, and a p-type electrode and an n-type electrode are formed. Here, near the resonator end face, the optical waveguide width is narrowed to approximately the same width as the current injection width to form a refractive index waveguide structure, and near the center, the optical waveguide width is made narrow enough to form a gain waveguide structure. .

With this structure, it is possible to obtain stable fundamental transverse mode oscillation and low astigmatism characteristics that reflect the refractive index waveguide structure, and at the same time, low noise due to longitudinal mode multiplexing that reflects the gain waveguide structure. characteristics are obtained. However, in the structure shown in FIG. 7, the conductivity type of the contact layer is the same as that of the second cladding layer, and the contact layer exists over the entire surface of the rib, so carriers injected from the p-type electrode are In the region of the gain waveguide structure where the optical waveguide width is wide, it spreads in the contact layer, which has low resistance, and is then injected into the active layer.
The reactive current increases, leading to an increase in rth. Furthermore, there is a problem in that the fundamental transverse mode tends to become unstable. Therefore, a structure has been devised in which the contact layer in the gain waveguide region is shaved into stripes to suppress the diffusion of injected carriers.

However, the above-mentioned conventional technology had the following problems. That is, (1) GaAs of the contact layer and the second layer 1. Since there is no etching method with a large difference in etching speed between AlGaAs and AlGaAs, there has been a problem in that it is difficult to control the etching depth with good reproducibility. For this reason, there was a problem that the contact layer remained or the cladding layer was removed too much.

(2) It is difficult to accurately control the width of the stripes in the contact layer, which causes a problem in that the reproducibility of the Ith value is poor.

The present invention is intended to solve these problems, and its purpose is to realize current confinement in the contact layer accurately and with good reproducibility, thus achieving stable fundamental transverse mode oscillation and low astigmatism. Has low aberration and noise characteristics, and has low 1th
An object of the present invention is to provide a method for manufacturing an LD that can oscillate.

[Problems to be Solved by the Invention] [Means for Solving the Problems] The method for manufacturing a semiconductor laser of the present invention includes forming a first cladding layer, an active layer, a second The second layer of a heterojunction structure with a laminated cladding layer and contact layer
It has a rib-shaped optical waveguide formed by removing part of the cladding layer of the optical waveguide, and the side surface of the rib-shaped optical waveguide is embedded with an n-vr group compound semiconductor, and near at least one resonator end face, The current injection width and the optical waveguide width are approximately the same to form a refractive index waveguide structure, and near the center of the resonator, the optical waveguide width is made sufficiently wider than the current injection width to form a gain waveguide structure. In the method for manufacturing a semiconductor laser, the width of the contact layer in the region having a wave structure is approximately the same as the current injection width in the region having the refractive index waveguide structure. A step of sequentially growing crystals of a cladding layer, an active layer, a second cladding layer, and a contact layer;
A step of etching the second cladding layer halfway through using masks with different widths, a step of removing the II-Ml group compound semi-compound semiconductor, and a step of etching the second cladding layer using masks having different widths; The gain guide is achieved by forming a wide striped mask, activating a reactive gas in a microwave-excited ECR plasma chamber with a separate discharge chamber, and irradiating an ion beam with a uniform direction. The method is characterized in that it includes a step of dry etching the contact layer in the wave region.

Furthermore, the material of the striped mask is an insulator such as photoresist, silicon oxide, silicon nitride, or aluminum oxide.

Furthermore, the reactive gas is characterized in that it contains at least one halogen element.

Furthermore, the pressure of the reactive gas is in the range of 5×1o-3 Pa to 1 Pa.

Furthermore, the incident power of the microwave is in a range of 1 W or more and 1 kW or less.

Further, the voltage for extracting the ion beam from the discharge chamber is in a range of 0 to 1 kV.

[Example] FIG. 1 is a cross-sectional structural diagram showing one embodiment of the present invention.

(a) is a top view, (b) and (C) are respectively A-A-
and BB- is a cross-sectional structure diagram. FIG. 2 is a manufacturing process diagram of the LD of the present invention.

The embodiment will be explained below using FIG. 2. At first,. On a GaAs substrate (101), an n-type GaAs buffer layer (102) and an n-type AlGaAs first cladding layer (10
3), AlGaAs active layer (104), p-type AlGaA
A second cladding layer (105) and a p-type GaAs contact layer (106) are sequentially laminated. For lamination, methods such as liquid phase epitaxy, metal organic chemical vapor deposition (hereinafter referred to as MOCVD), and molecular beam growth are possible. Subsequently, a dielectric thin film such as silicon dioxide is formed on the wafer on which each of the above-mentioned layers has been laminated, and a second
The rib etching shape (10
In 8), the dielectric thin film is patterned by a normal photolithography process to form a rib etching mask (107) (FIG. 2(a)). Next, the laminated wafer is placed in the shape of the rib etching mask (107).
The second cladding layer (105) is etched halfway to form ribs (FIG. 2(b)). Here, with the etching mask (107) still placed on the rib,
To grow the ZnS and eSel-x layers, which are I-VI compound semiconductors, the Zn5xSel-8 layer was grown using an adduct of dimethyl zinc and dimethyl selenium as raw materials.
OCVD method was used. Composition of S in ZnS, Se1□
When is 0.06, it is lattice matched with GaAs and a high quality crystal layer can be obtained. Furthermore, by using adducts as raw materials,
Since crystal growth is possible at a low substrate temperature of around 250'C, there is little residual stress due to differences in thermal expansion coefficients, and a longer life of the active layer can be achieved. In this case, on the second cladding layer outside the rib, single crystal Z n SxS e I-x
A layer (109) is grown, and a polycrystalline ZnSxSe1-x layer (
110) grows (Fig. 2(d)). Subsequently, the polycrystalline Zn5xSel-2 layer above the rib is selectively etched away using an etching solution such as an aqueous NaOH solution. FIG. 2(e) is a top view of the LD after etching, and the shaded area is a portion of the single crystal znSxSe+-x layer (109) that remained unetched. Next, the p-type contact layer (106) is removed by etching, leaving a stripe pattern.First, the mask (113) is removed by etching.
A dielectric material is used to form stripes as shown in the top view of FIG. 2(g). Therefore, the contact layer is shown in Figure 2 (
As shown in (109) of g), a part of the gain waveguide is exposed. After that, this exposed contact layer is etched by reactive ion beam etching (hereinafter referred to as RIB) using chlorine.
(denoted as E) (see Figure 2 (h)).
)). As the dielectric material, 5102, 813N4, or Al2O3 can be used. These dielectrics function as a mask because the RIBE etching rate is extremely slow. By using RIBE, the (106) GaAs contact layer and the (105) A
Since the etching rates of the IGaAs cladding layers are different, an etching stop can be applied at the boundary. Therefore, it is possible to manufacture the cross-sectional structure of the cabinet 1 shown in FIGS. 1B and 1C with good reproducibility.

Finally, a p-type ohmic electrode (111) and an n-type ohmic electrode (112) were formed, and the LD of the present invention could be manufactured.

Since the LD of the present invention has a refractive index waveguide structure near the resonator end face, stable transverse mode oscillation and low astigmatism characteristics can be obtained. On the other hand, near the center of the resonator, since the structure is a gain waveguide structure, the longitudinal modes are multiplied, and low noise characteristics are obtained in which fluctuations in optical output with respect to returned light are extremely small. Furthermore, by making the contact layer width of the gain waveguide structure region almost equal to the rib width of the refractive index waveguide structure region, the spread of carriers within the gain waveguide region is limited to the extent that longitudinal multimode can be obtained. Because of this, Ith can be lowered and quantum efficiency can be improved compared to the case where the contact layer is entirely present on the rib. Furthermore, the metal of the p-type electrode and the second
Since a Schottky barrier is formed between the cladding layers, there is almost no leakage current from sources other than the electrodes in contact with the contact layer. Therefore, stable fundamental transverse mode oscillation was possible even at high outputs.

Next, RIBH of the contact layer of the present invention will be explained based on the drawings.

FIG. 6 shows a schematic configuration diagram of a RIBE apparatus in an embodiment of the present invention. Since a gas containing a highly reactive halogen element is used as an etching gas, a sample preparation room (60
1) and the etching chamber (602) are connected to the gate valve (60
3), and the etching chamber (602) is always kept in a high vacuum state. (603
) is an electron/cyclotron resonance (hereinafter referred to as ECR) plasma chamber, which is surrounded by a cylindrical donut-shaped coil (604) for generating a magnetic field, and the connection part with a microwave waveguide (605) is a plasma chamber for introducing microwaves. There is a quartz window for use. Electrons ionized and generated by microwaves repeatedly collide with gas while performing cyclotron motion due to an axisymmetric magnetic field. This rotation period is, for example, when the magnetic field strength is 875 Gauss.
Matches the microwave frequency, for example 2.45 GHz,
Electronic systems absorb microwave energy resonantly.

For this reason, the discharge can be sustained even at low gas pressures, high plasma density can be obtained, and the reactive gas can be used for a long time. Furthermore, the electrons and ions are focused at the center due to the high electric field distribution at the center, so that the sputtering effect of the ions on the side walls of the plasma chamber is small, and highly clean plasma can be obtained. E
Ions generated in the CR plasma chamber (603) are accelerated by a mesh-like extraction electrode (606) and are transferred to the sample (607).
) is irradiated. The sample holder (608) can change the direction of the ion beam incident on the sample using a manipulator (609).

Practically effective etching conditions for etching the contact layer are as follows.

As shown in FIG. 3, the higher the gas pressure, the faster the etching rate. However, if the gas pressure becomes too high, no discharge will occur, and even if a discharge occurs (more than lpa), the ion sheath width and the mean free path of the ions and neutral particles will be approximately equal, and the ion beam will have no directivity. It is not suitable for microfabrication. If the gas pressure is low (below 1 x 10-3 pa), the etching rate is too slow and is not suitable for practical use.

As shown in FIG. 4, the higher the input power of the microwave, the more intense the excitation, the higher the plasma density, and the faster the etching rate.

However, if the output is too high, the plasma temperature will rise, causing thermal deformation of the electrodes, and the substrate temperature will also rise due to radiant heat, making temperature control difficult.

Good mechanical properties were obtained in the range of 1 W to 1 kW.

Regarding the extraction voltage, as shown in FIG. 5, the higher the voltage, the faster the etching rate. However, the voltage is 1
If it exceeds kV, physical Snok vine ringing becomes strong, causing deep damage to the substrate crystal, which is undesirable. If no extraction voltage is applied, if the substrate temperature is raised to about 200℃,
Etching occurs due to radical species, and the etching progresses isotropically.

In this example, chlorine gas is used as the etching gas, but gases containing halogen elements, such as BC
13, CCl2F2, etc. may also be used.

[Effects of the Invention] As described above, according to the present invention, the following effects can be obtained.

(1) Because the RIBE method was used to partially etch away the contact layer of the gain waveguide section of the low-noise LD, instead of the conventional wet etching method, the etching stopped at the second cladding layer. The current injection width can be controlled with good reproducibility.

(2) A Schottky barrier is effectively formed between the second cladding layer and the electrode, thereby reducing the spread of carriers and keeping Ith low.

(3) By limiting the conditions of the RIBE method, the width of the contact layer can be precisely processed.

(4) The dielectric mask is hardly etched by RIBE, and this also allows the width of the contact layer to be accurately controlled.

[Brief explanation of drawings]

FIGS. 1(a) to 1(c) are structural diagrams showing one embodiment of the LD of the present invention. FIGS. 2(a) to 2(f) are manufacturing process diagrams showing one embodiment of the LD of the present invention. FIG. 3 is a diagram showing the relationship between etching rate and gas pressure in RIBE showing an embodiment of the present invention. FIG. 4 is a diagram showing the relationship between etching speed and microwave incident output in RIBE, which shows one embodiment of the present invention. FIG. 5 is a diagram showing the relationship between etching speed and extraction voltage in RTBH according to an embodiment of the present invention. FIG. 6 is a schematic diagram of the RIBE apparatus used in the embodiment of the present invention. FIGS. 7(a) to 7(C) are structural diagrams of conventional LDs. (101)(701)-n-type GaAs substrate (102)(
702) ---n-type GaAs buffer layer (103) (703)... n-type AlGaAs first cladding layer (104) (704) ---AIGaAS active layer (10
5) (705) --- p-type AlGaAs second cladding layer (106) (706) ---1) type GaAs = + contact layer (107) ... Rib etching mask (108
) ... Rib etching shape (109) (707)
---Single crystal Zn5xSe+-8 layer (110)---Polycrystalline ZnSxSel-X layer (111)...N-type ohmic electrode (112)
...N-type ohmic electrode (113) ...Dielectric mask (114) ...Chlorine ion beam (601)
...Sample IL@Preparation room (602) ...Etching room (603) (604) (605) (606) (607) (608) (609) (610) (611) (612) ・Gate valve・Electromagnet...Microwave waveguide, extraction electrode, sample, sample holder...manipulator, gas introduction part, transport rod (613)...Exhaust system and above

Claims (6)

[Claims] (1) A rib formed by removing part of the second cladding layer of a heterojunction structure in which a first cladding layer, an active layer, a second cladding layer, and a contact layer are laminated on a III-V compound semiconductor substrate. The side surface of the rib-shaped optical waveguide is embedded with a II-VI compound semiconductor, and the current injection width and the optical waveguide width are approximately the same in the vicinity of at least one resonator end face. Near the center of the resonator, the optical waveguide width is made sufficiently wider than the current injection width to form a gain waveguide structure, and the width of the contact layer in the region having the gain waveguide structure is , in a method of manufacturing a semiconductor laser having a current injection width comparable to the current injection width of the region having the refractive index waveguide structure, the first cladding layer, the active layer, the second cladding layer, and The process of successive crystal growth of the contact layer and the process of growing the second contact layer using masks of different widths
a step of etching away part of the cladding layer; a step of burying the II-VI compound semiconductor; and a step of forming a striped mask having a width comparable to the current injection width of the region having the refractive index waveguide structure. By activating the reactive gas in a microwave-excited electron cyclotron resonance (hereinafter referred to as ECR) plasma chamber with a separate discharge chamber and irradiating it with an ion beam having a uniform direction, the gain guide A method for manufacturing a semiconductor laser, comprising the step of dry etching a contact layer in a wave region. (2) The material of the striped mask is an insulator selected from photoresist, silicon oxide, silicon nitride, and aluminum oxide.
A method of manufacturing the semiconductor laser described above. (3) The method for manufacturing a semiconductor laser according to claim 1, wherein the reactive gas contains at least one halogen element. (4) The pressure of the reactive gas is 5×10^-^3Pa
2. The method of manufacturing a semiconductor laser according to claim 1, wherein the pressure is within a range of from 1 Pa to 1 Pa. (5) The method for manufacturing a semiconductor laser according to claim 1, wherein the incident power of the microwave is in a range of 1 W or more and 1 kW or less. (6) The method of manufacturing a semiconductor laser according to claim 1, wherein a voltage for extracting the ion beam from the discharge chamber is in a range of 0 V or more and 1 kV or less.