JPH05304335A - Fabrication of semiconductor laser - Google Patents

Abstract

PURPOSE:To fabricate a semiconductor laser in which a current constriction layer for constricting the pumping current produced through high energy injection is formed easily with high accuracy. CONSTITUTION:When a high resistance layer 11 is formed in the vicinity of a laser active layer 3 by implanting high energy ions into a semiconductor substrate having quantum well structure, the high resistance layer 11 can be formed highly accurately through a simplified process by commonly using an electrode metal 9 as a mask for selecting the high resistance layer 11 forming region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser used for optical communication and information processing.

[0002]

2. Description of the Related Art In a conventional compound semiconductor laser, a quantum well structure capable of generating laser light, for example, a double hetero structure including an active layer for generating laser light is formed by an MBE (molecular beam epitaxy) device or the like. , A high resistance layer for narrowing and concentrating a pumping current in the laser active layer in the structure is formed in the vicinity of the surface, and further an electrode for introducing the pumping current into the substrate is provided. .

An AlGaAs laser will be described below as a concrete example. The double hetero structure is, for example, as shown in FIG. 3, a compound semiconductor substrate (n-G) used as a substrate.
aAs) on the buffer layer (n-GaAs ~ 1 μm)
As the first laminated structure, and then the cladding layer (n-
AlGaAs ~ 1 μm), laser active layer (GaAs ~
0.15 μm), cladding layer (p-AlGaAs ~ 1)
μm) in this order, and a cap layer (p-GaAs to 0.35 μm) is further formed on the top. Therefore, the active layer exists at a depth of 1 μm or more from the uppermost clad layer.

In order to efficiently generate a laser beam on the semiconductor substrate in which the double hetero structure is formed in this manner, the pumping current is squeezed. (1) Oxidation formed on the substrate surface Method of limiting flow path of pumping current by silicon film (FIG. 4) (2) Diffusion of zinc etc. from the substrate surface to form P-type disordered layer to form a reverse bias structure of PNPN Methods are used.

However, in both the methods (1) and (2), the current is squeezed from the surface of the substrate, and therefore 1 μm.
In the vicinity of the active layer for generating laser light, which is formed in the deep part of the substrate of m or more, the pumping current spreads as shown in FIG. 4, and efficient generation of laser light (lowering of laser oscillation threshold and quantum There is room for improvement in the improvement of the efficiency of chemical conversion).

Therefore, in recent years, attempts have been made to form a confined layer of pumping current in the vicinity of the active layer by implanting ions forming a high-resistance insulating layer in the semiconductor substrate into a deep portion of the substrate. Applied Physics Lette
As seen in rs, Vol.54, PP730 (1989), AlGa
By implanting oxygen ions into the As double heterostructure,
A high resistance layer is formed in the deep portion of the substrate (FIG. 5) to achieve a low threshold of laser oscillation and an improvement in quantization efficiency.

[0007]

Since the process parameters of the above-mentioned ion implantation method can be controlled as an electrical physical quantity, the ion implantation method can be accurately and reproducibly provided in the vicinity of the active layer in the substrate on which the double hetero structure is formed. A current constriction layer can be formed. However, since the ions have to reach the vicinity of the active layer existing deep in the substrate,
The ion energy is a region (several MeV) higher by one digit or more than the implantation energy region (several hundreds keV) that has been often used in silicon semiconductors.

Therefore, in order to selectively implant such MeV energy ions in a region-selective manner, that is, without implanting into the laser emission portion which is a concentrated flow path of the pumping current, a high resistance layer is formed, and a current of the current is formed. In order to inject only into the portion that prevents dissipation, the film thickness is on the order of several μm in the case of the conventional organic resist mask, and its photolithography has various technical problems (resisting multiple times). There is a need for coating, setting various conditions for exposing a mask structure having a high aspect ratio, etc.). For example, the oxygen ion of 1.5 MeV is added to AlGaAs described above.
When injected into the double hetero structure, the distribution has the maximum concentration around 1.8 μm (Fig. 6), 1.35 μm to 1.35 μm.
It becomes possible to form a high resistance layer in the vicinity of the active layer existing over 50 μm. On the other hand, with a normal organic photoresist (eg, AZ1350), the mask thickness for blocking this oxygen ion is 3 μm. It is clear from the calculation of FIG. 7 that it extends. That is, FIG. 7 shows AZ13.
The calculated distribution of the concentration of the implanted 1.5 MeV oxygen in 50 is calculated to obtain a mask thickness of about 3.0 μm at which the concentration is almost negligible. This thickness cannot be produced unless the resist coating work is normally performed twice or more in order to ensure the accuracy of the film thickness. In addition, a resist structure having a high aspect ratio of 3 μm must be formed. It was difficult to set the exposure conditions, and it was an item that should be improved in the current constriction layer manufacturing process by ion implantation. That is, a mask capable of blocking ions with a film thickness as thin as possible has been demanded in the process of forming a narrowed layer of a pumping current by high-energy ion implantation.

The present invention has been made to solve the above problems, and an object of the present invention is to easily and accurately manufacture a current constriction layer by high energy implantation. And to provide a semiconductor laser capable of generating laser light with high efficiency.

[0010]

The semiconductor laser manufacturing method of the present invention made to solve the above-mentioned problems is (1)
A quantum well structure capable of generating laser light, for example, a double hetero structure including an active layer for generating laser light, is
(Molecular beam epitaxy) device or the like, and then (2) forming an electrode metal for introducing a pumping current into the substrate on the surface of the double hetero structure, and (3) forming the electrode. By performing high-energy implantation using metal as a mask for selecting the implantation region, the active layer directly under the electrode metal serves as a concentrated channel for pumping current, and the other portions serve as high-resistance layers that block pumping current. A mask for selecting a region for forming a high resistance layer by a high energy ion implantation method using a metal electrode arranged on the surface of a substrate in order to introduce a pumping current into the substrate in a self-alignment process. It is characterized by being shared as.

[0011]

In the present invention, since the metal electrode for introducing the pumping current is also used as a mask for blocking high-energy ions, the coating operation for ensuring the accuracy of the resist film thickness and the aspect ratio control as in the conventional case are performed. It is not necessary to consider the problem, and the current constriction layer can be easily formed with high accuracy.

[0012]

EXAMPLES Before describing the examples, the film thickness required when masking high-energy ions with a metal is calculated. For example, when 1.5 MeV oxygen ions are implanted into Au, the concentration distribution of oxygen in Au can be calculated as shown in FIG. 8 and the mask thickness is about 1.5 μm at which the concentration is almost negligible. .. This is about half the value of the organic resist shown in FIG.

Now, as an example of the method for forming the current narrowing layer of the semiconductor laser according to the present invention, it is assumed that the current narrowing layer is formed by injecting 1.5 MeV oxygen into the AlGaAs double hetero structure. This will be described with reference to 1. 1A shows a cap layer 1, a clad layer 2, a laser active layer 3, a clad layer 4, a buffer layer 5, and a compound semiconductor substrate 6.
The double-hetero structure is formed by forming a quantum well structure capable of generating laser light on a compound semiconductor substrate by an MBE (Molecular Beam Epitaxy) device or the like.
Then, (b) about 1.5 μm (electrode metal Au
(Corresponding to the mask thickness of 1) The organic resist film 7 is applied with a film thickness of the above. This is a thickness that can be applied after ensuring sufficient film thickness accuracy once. Next, (c) a stripe window 8 corresponding to a laser emission region is opened in this organic resist film by using a normal lithography method. In this case, since the aspect ratio is not high, it is easy to set the exposure condition.

On the organic resist film thus formed, for example, (d) the electrode metal Au5 is formed on the entire surface of 1.
It is vapor-deposited to a thickness of 5 μm. However, since an ohmic contact is made, the interface with the p-GaAs cap layer is
It is preferably an Au / Zn alloy. Where (e)
When the organic resist film is peeled off by the conventional lift-off method, only Au deposited on the stripe window 8 is 1.5
With the mask thickness of oxygen ion of MeV, it remains on the substrate surface.

By (f) injecting the oxygen ions into this substrate, the ions cannot reach the portion directly below the masked with the electrode metal Au5 and stop in the electrode metal Au5, but otherwise. In the area of, the area reaches the vicinity of the active layer in the deep part of the substrate and forms a high resistance layer, which causes the pumping current to be concentrated and squeezed in the active layer directly under the electrode metal, thereby reducing the laser emission. Thresholding and quantization efficiency can be improved.

Needless to say, the implanted ions are not limited to oxygen, and any ions that form a high resistance layer can be used depending on the substrate material. However,
It is necessary to optimally control the ion implantation energy / ion dose, the annealing temperature, and the like. In the semiconductor, the implanted ions need to have a concentration capable of affecting the energy level of electrons and forming a high resistance layer. However, at such a concentration, the electrical conductivity of a conductor metal such as Au is high. There is no limitation on the conduction characteristic, and even Au or the like into which oxygen is injected retains good electric conduction characteristic as an electrode metal.
Therefore, even if Au is used as a mask material for oxygen ions, the electrical characteristics of the electrode do not change due to the implantation, and Au can be used both as the implantation mask and the electrode.

In the method for forming the current narrowing layer according to the present invention, the electrode metal formed by performing the lift-off method with the organic resist in the normal film thickness range (about 1.5 μm) is also used as the mask material. There are features. That is, a high-energy ion, which is difficult to block with an organic resist in the film thickness range, is surely blocked in the laser emission stripe region, and a high-resistance layer can be formed in the other regions with an implantation region selection mask. In addition to being provided, the active layer immediately below the electrode metal serves as a laser emission region, so that there is an advantage that the process can be simplified and a self-aligned process requiring no alignment can be provided.

[0018]

[Modification] FIG. 2 shows a modification of the present invention. In the case where the electrode metal width required for lead wire bonding or the like must be wider than the stripe width of the laser active region, a double hetero structure is used. After the structure is formed as shown in FIG. 2A, (1) it has a film thickness sufficient to maintain ohmic characteristics with p-GaAs, and (2) it has a width sufficient to bond a lead wire, and (3) The electrode metal Au12 (Au / Zn is desirable at the interface), which is thin enough to allow high-energy ions to completely pass therethrough, is vapor-deposited on the entire surface (a '), and the above-mentioned (b) is used. ) (C)
Through the steps (d), (e), and (f), a convex structure Au mask is formed by the photolithography lift-off method, and high-energy ion implantation is performed from above the convex structure Au mask. In this way, the current confinement layer is formed in the stripe width of the laser active area, and the lead wire bonding area wider than the stripe width can be formed.

In the above embodiment, the lift-off method is used for forming the electrodes, but it is needless to say that the electrodes may be formed by a sputtering method, an etching method or the like without being limited to this.

[0020]

The method for forming a current constriction layer according to the present invention comprises:
In principle, the ion implantation method, which has a proven track record in silicon semiconductor manufacturing, is used, and the metal electrode that introduces the pumping current is also used as a mask that blocks high-energy ions. It can be performed easily and with high precision, and since the pumping current can be narrowed in the vicinity of the active layer, various characteristics of laser oscillation of a semiconductor laser (laser oscillation threshold value, quantization efficiency) can be improved. The effect is obtained.

[Brief description of drawings]

FIG. 1 is an embodiment of a semiconductor laser manufacturing method of the present invention.

FIG. 2 is a modified example of the semiconductor laser manufacturing method of the present invention.

FIG. 3 Conventional AlGaAs double hetero structure diagram

FIG. 4 Current narrowing method using conventional silicon oxide film

FIG. 5: Current narrowing method by conventional high-energy oxygen injection

FIG. 6 is a concentration distribution diagram of high energy oxygen ions implanted in an AlGaAs double heterostructure.

FIG. 7 is a concentration distribution diagram of high-energy oxygen ions implanted in the organic resist AZ1350.

FIG. 8 is a concentration distribution diagram of high-energy oxygen ions implanted in the electrode metal Au.

Claims (1)

[Claims] 1. A semiconductor substrate having a quantum well structure capable of generating laser light, a high resistance layer for narrowing a pumping current for efficient laser light generation is provided in the vicinity of the laser active layer by an ion implantation method. In the semiconductor laser device to be formed on the substrate, the metal electrode arranged on the surface of the substrate is used as an implantation region selection mask for forming a high resistance layer by the ion implantation method in order to introduce a pumping current into the substrate. Semiconductor laser manufacturing method.