JPH012386A - Manufacturing method of semiconductor laser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a semiconductor laser in which a refractive index waveguide mechanism and an internal current confinement layer are provided above an active layer using a technique of disordering a superlattice structure. Relating to a manufacturing method.

(Prior Art) Research and development of various electronic devices using superlattice structures has been progressing. Among these, semiconductor lasers with a quantum well structure have other characteristics such as being able to control the oscillation wavelength, having a low threshold value, and having a stable threshold current with respect to the ambient temperature. Attention has been paid.

It is known that when impurities are diffused or ions are implanted into this superlattice structure, it becomes disordered and becomes a mixed crystal.

The manufacturing technology of semiconductor lasers that uses the technology to disorder such a superlattice structure (referred to as MQW) to create a refractive index waveguide mechanism and an internal current confinement layer is described in the literature: (Japanese Journal of Flight Physics).
panese Journal of Applied
Physics) J 26. (8), 1986
．． pp, L690-1692). Prior to explaining the present invention, the conventional semiconductor laser manufacturing technique disclosed in this document will be briefly explained with reference to FIG.

FIGS. 3A to 3C are manufacturing process diagrams of a conventional semiconductor laser. On the n-GaAs substrate 10, as soil, n
Aj2o, Gao5As cladding layer 12, undoped active layer 14 having a superlattice structure of GaAs and Al1.2Gaa8As, p-Aβ. 2Gao, aAS optical waveguide layer 16, GaAs and Aβ. An optical waveguide layer 18 having a p-type superlattice structure consisting of
(A)), the striped central region 18 of the optical waveguide layer 18 (the stripe direction is perpendicular to the plane shown)
Si ions are implanted into the other region +sb outside a (
Figure 3 (B)). Subsequently, p Affo, 4 Gao, e As cladding layers 20 and p-GaAs layers 22 are sequentially regrown by molecular beam epitaxial method on the optical waveguide layer 18 after the S1 ion implantation, and then at a temperature of 850°C. The implanted S1 ions are activated by annealing, and are diffused throughout the optical waveguide layer to disorder the superlattice in region +8b. The region +8b disordered by this high-temperature annealing becomes the current confinement layer 24, and the striped central region 18a which is not disordered becomes the superlattice optical waveguide 26 as a refractive index waveguide mechanism. Thereafter, required electrodes 28 and 30 are provided on the upper side of the cap layer 22 and the lower side of the substrate 10, respectively, to form a semiconductor laser having a structure as shown in FIG. 3(C).

In this way, it is possible to obtain a buried type superlattice guiding waveguide with a striped structure without using an etching process, and a semiconductor laser equipped with such a buried type superlattice optical waveguide can secure a high power output with a horizontal moat. At the same time, it has the advantage of having a completely Brenna structure.

(Problem to be solved by the invention) However, in this conventional method, the amount of S1 ions implanted is as large as 3 x 10" cm, -2, so the optical waveguide of the superlattice structure in which the ions are implanted is The surface of the region of the layer, and therefore the interface with the regrown crystalline layer, such as the cladding layer, is degraded, and this causes the crystallization of the crystalline layer, such as the cladding layer, on the central region of the optical waveguide layer, which is not ion-implanted. There was a problem in that the quality was affected, and as a result, the reliability of the operating characteristics decreased.

In addition, if the amount of ions implanted is large, there is a risk that the ions will reach the lower active layer and damage it, and even worse, the superlattice will be damaged by the implanted ions, suppressing disorder. This poses a problem in that the optimum design of the semiconductor laser structure is restricted.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, an object of the present invention is to provide a method for manufacturing a highly reliable semiconductor laser having a structure in which a superlattice index waveguide mechanism is embedded.

(Means for Solving the Problems) In order to achieve this object, according to the semiconductor laser manufacturing method of the present invention, the following measures are taken.

First, a superlattice optical waveguide layer is provided above an active layer provided above a substrate, and a striped mask is provided on the surface of the central region.

Next, impurity diffusion source layers are provided on both sides of the mask on the surface of this superlattice optical waveguide layer by low pressure organometallic vapor phase epitaxy.

Next, impurities are thermally diffused from this impurity diffusion source layer in order to disorder the superlattice in the region of the superlattice optical waveguide layer outside the central region.

(Function) In this method, an impurity diffusion source layer with an appropriate concentration is provided on the surface of the region outside the striped central region of the optical waveguide layer having a superlattice structure, and this impurity diffusion is achieved by appropriately performing heat treatment. The superlattice in the optical waveguide layer region below the source layer is disordered by impurity thermal diffusion and becomes a current confinement layer.
The undisordered central region becomes a superlattice index waveguide mechanism.

Therefore, there is no risk of deterioration of the interface, damage to the active layer, or damage to the superlattice as occurs in the case of ion implantation, and the degree of freedom in designing the semiconductor laser is increased (and reliability is also improved).

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1A to 1E are manufacturing process diagrams of the semiconductor laser of the present invention, and FIGS. 2A and 2E are enlarged cross-sectional views of the main parts of the semiconductor laser. It should be noted that these figures are only schematic illustrations to the extent that the present invention can be understood, and therefore, the dimensions, shapes, MU distribution ratios, numerical conditions, and other conditions of each component are as explained in the following explanations and figures. The present invention is not limited to the illustrative examples only. Further, each figure is a cross-sectional view of a wafer at a main stage of the manufacturing process, but with the exception of a part, hatching and the like representing the cross section are omitted.

In the embodiments described below, an example in which an AnGaAs layer is formed on a GaAs substrate will be described.

An n-GaAS substrate is used as the substrate 40, and a lower cladding layer 42 and an active layer 44 are formed on this substrate 40 by ordinary metal organic vapor phase epitaxy or molecular beam epitaxial method.
, an optical waveguide layer 46, and a superlattice optical waveguide layer 48 are sequentially grown (FIG. 1(A)). In this case, the lower cladding layer 42 is made of an n-ha β Approximately 6 nm thick
44a) and a quantum well layer of GaAs (with a layer thickness of about 80 mm)
The active layer has a multiple quantum well structure containing 44blFr. The number of these quantum well layers 44b and the barrier layer 44
The thickness of a is set to be smaller than the oscillation threshold current, and the quantum well width is determined depending on the oscillation wavelength.

Furthermore, the optical waveguide layer 46 is made of p-Aρ having a layer thickness of about 1100 nm.
It is assumed that the layer is yGa+-yAs. In addition, the superlattice optical waveguide layer 48
is a p-type layer, and as shown in the enlarged cross-sectional view of FIG.
7 and GaAs quantum well layer 49, and both layers 47 and 4 are formed so that the average composition is AβyGa+-, As.
For example, the layer thickness of both layers is set to be about 6 nm), and the carrier concentration is set to, for example, I
-3 and the O layer is grown to a total thickness of about 500 nm.

Further, it is preferable to set the quantum well width so that the refractive index of the superlattice is larger than the refractive index of the average composition at the oscillation wavelength, and smaller than the refractive index of the active layer 44. be.

Next, as shown in FIG. 1B, a striped mask 50 is provided on the surface of the central region 48a of the superlattice optical waveguide layer 48 provided above the active layer 44. In this example, a 5L3N4 film is provided on the superlattice optical waveguide layer 48 by an appropriate method, and then this 5i3Na film is patterned to a predetermined width, for example, about 3 um, using a photolithography technique, as shown in the figure. A striped mask 50 extending in a direction perpendicular to the plane of the paper is formed.

Next, a low pressure ( An impurity diffusion source layer 52 doped with impurities at a high concentration is selectively grown under appropriate conditions using a metal organic vapor phase epitaxy method (reduced pressure) (FIG. 1(C)). In this embodiment, it is preferable that the impurity is Si, the thickness of the impurity diffusion source layer 52 is, for example, about 30 nm, and the concentration of Si is about 5xlO''cm-3.

Next, in order to disorder the superlattice of the superlattice optical waveguide layer 48 outside the central region 48a, thermal diffusion of Si ions is performed from the impurity diffusion source layer 52. Therefore, a cap layer (for example, 5
13Na layer) 54, the entire wafer is heated at a temperature of about 850° C. for about 30 minutes in an electric furnace, for example.
High temperature annealing is performed (FIG. 1(D)). It is also possible to carry out the heat treatment by means of a lamp, laser or any other suitable means instead of an electric furnace. By this thermal diffusion treatment, S1 ions, which are impurities, from the impurity diffusion source layer 52 are diffused almost downwardly in the side region 48b of the superlattice optical waveguide layer 48, and the superlattice 48 in this region 48b is
a and 48b are disordered to form a mixed crystal. The side regions 48b of this disordered superlattice form a current confinement layer (in this example, the disordered n A R'/G a of the superlattice).
+ -v A 8 layers) 56. On the other hand, since this impurity does not substantially thermally diffuse in the lateral direction, the central region tft
48a is substantially unaffected and remains as a superlattice, and therefore, a portion of this central region 48a becomes a superlattice refractive index optical waveguide mechanism, that is, a superlattice optical waveguide 58. Note that this portion is shown in an enlarged manner in FIG. 2(B).

Next, after removing the cap layer 56, mask 50, and impurity diffusion source layer 52 by a suitable method such as dry etching, a current confinement layer is formed by a suitable method such as metal organic vapor phase epitaxy or molecular beam epitaxial method. 56 and an upper cladding layer 60 and a contact layer 62 above the superlattice optical waveguide 58.
Let them grow sequentially. The upper cladding layer 60 and the contact layer 62 have a suitable thickness according to the design.
J2 x Gar-11A 8 layer and p-0843
For example, the thickness of the upper cladding layer 60 is about 1 um. Thereafter, an n-type upper electrode 64 is formed on the contact layer 62 and a p-type lower electrode 66 is formed on the lower surface of the substrate 40 by, for example, a vapor deposition method to complete the semiconductor laser (FIG. 1(E)). .

As is clear from the above description, according to the present invention, instead of ion implantation, impurity diffusion sources are provided at required locations on the surface of the optical waveguide layer having a superlattice structure by metal-organic vapor phase epitaxy, and the diffusion This method uses thermal diffusion of impurities from a source to disorder the superlattice to create a refractive index waveguide mechanism and to form a current confinement layer, so the deterioration of the interface between the current confinement layer and the layer above it is minimized. Therefore, the quality of the crystal in the region where impurities are not diffused is maintained at a high quality, resulting in a longer life and increased reliability. Furthermore, with the method of the present invention, damage to the superlattice and active layer due to thermal diffusion of impurities does not occur, so the design of the laser structure can be optimized.

In addition, since the semiconductor laser obtained by this invention is a semiconductor laser equipped with a superlattice refractive index waveguide mechanism and an internal current confinement layer, it is possible to secure a transverse fundamental mode up to high output as in the past, and also has a brainer structure. It is.

The present invention is not limited only to the embodiments described above, and may be modified and modified in many ways. The invention is also suitable for application to semiconductor lasers having a structure including an InGaAlP layer on a GaAs substrate, or an InGaAlAs layer or an InGaAsP layer on an InP substrate.

In general, the laminated structure of the semiconductor to be manufactured is not limited to the structure described in the examples, but may be a structure that includes at least a superlattice refractive index waveguide mechanism and a current confinement layer above the active layer. Good.

Furthermore, the conductivity type of each layer can be set as n-type or p-type depending on the design, and correspondingly, any other suitable impurity can be selected for Zn other than 81, which is the impurity to be thermally diffused. I can do it.

Further, although the example has been described using Si3N as the mask material, any suitable material can be used depending on the design.

Further, the numerical values in the above-mentioned embodiments are merely preferred examples, and therefore, they can be set to any suitable value in consideration of the layer structure, material, conductivity type, and other necessary conditions. .

(Effects of the Invention) As is clear from the above description, according to the semiconductor laser manufacturing method of the present invention, instead of ion-implanting impurities, an impurity diffusion source is provided, and the impurities are thermally diffused from this impurity diffusion source. Since this is a method of disordering the superlattice by causing disorder, the crystal quality of the layer grown above the disordered layer region can be maintained at high quality, and damage to each layer due to impurity thermal diffusion does not occur. The degree of freedom in designing the semiconductor laser increases. Furthermore, since there is no fear of deterioration of crystal quality or damage to layers, it is possible to extend the life of the laser element and thereby improve reliability.

[Brief explanation of the drawing]

FIGS. 1(A) to (E) are manufacturing process diagrams for explaining one embodiment of the method for manufacturing a semiconductor laser of the present invention, and FIGS. 2(A) and (B) are diagrams showing the steps shown in FIG. 1. Enlarged cross-sectional views of main parts of the wafer structure at the manufacturing process stage, Figures 3(A)-(
C) is a manufacturing process diagram of a conventional semiconductor laser. 40... Substrate, 42... Lower cladding layer 44... Active layer, 44a... Barrier layer 4
4b--Quantum well layer, 46... Optical waveguide layer 47-
...Ill wall layer 48 (of the superlattice optical waveguide layer)...Superlattice optical waveguide layer, 48a...Central region 48b...Side region 49...J1 child (of the superlattice optical waveguide layer) Well layer 50...
・Mask, 52... Impurity diffusion layer 54...
- Cap layer 56...Current confinement layer (side region of disordered superlattice) 58...Superlattice refractive index waveguide mechanism (superlattice optical waveguide or central region of non-disordered superlattice) 60... Upper cladding layer, 62... Contact layer 64... Upper electrode, 66... Lower electrode. Patent applicant Oki Electric Industry Co., Ltd. 44a:ji”
4 layers 44b Quantum quantum layer Manufacturing process diagram of this invention Figure 1 56 Current confinement layer 5 days Superlattice leading waveguide (refractive index optical waveguide mechanism) fΔ 60 Upper cladding layer 62 Contact layer 64
Upper electrode 66 Lower electrode Manufacturing process diagram of this invention Figure 1 4711! Wall layer 49 Enlarged cross-sectional view of essential parts of quantum well layer Figure 2/ll'D It'd Igbl
(

Claims (1)

[Claims] (1) When manufacturing a semiconductor laser by providing a refractive index waveguide mechanism and an internal current confinement layer above the active layer using a technique to disorder the superlattice structure, A striped mask is provided on the surface of the central region of the lattice optical waveguide layer, impurity diffusion source layers are provided on both sides of the mask on the surface of the superlattice optical waveguide layer by low-pressure organometallic vapor phase epitaxy, and an impurity diffusion source layer is provided outside the central region. A method for manufacturing a semiconductor laser, comprising thermally diffusing impurities from the impurity diffusion source layer in order to disorder the superlattice of the superlattice optical waveguide layer.