JPS5979590A - 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 The present invention relates to a semiconductor laser including a substrate having a circular protrusion on its surface extending between both ends thereof, and a method for manufacturing the laser.

Semiconductor lasers generally consist of a group IV compound and include a substrate of semiconductor material with a thin active layer between two layers of opposite conductivity type, i.e. a P-type layer on one side of the active layer. There is a VcN type layer on the other side, but such lasers generally emit light in two or more optical modes;
This limits its use. U.S. Patent No. 42.15
No. 319 discloses a laser that emits a stable single mode output beam. The output flux from this laser is controlled by grading the layer thickness. The laser is fabricated by depositing a confinement layer and an active layer on a substrate having a pair of halves substantially parallel to the surface;
The inclination is caused by the difference in growth rate between the layer on the region between the grooves and the layer above the groove when each layer is formed by liquidus or vapor phase epitaxial method.

However, when each layer is deposited using a liquid phase or vapor phase epitaxial method on an indium phosphorous substrate having a pair of parallel grooves, the multi-grooves are filled more quickly than the flat substrate, and the grooves are filled continuously. This results in a smooth surface, making it impossible to obtain a flat surface. This growth habit of InP limits the utility of the structure of the US patent 1 for lasers consisting of InP and related alloys, and the sloped layer of the laser of the US patent 9 for lasers consisting of InP and related alloys. It is preferable to show the structure.

It has been discovered that when a laser is formed on a substrate having ridges on its surface, the surface of each deposited layer is curved to obtain a slope of the required thickness. The semiconductor laser of the present invention includes a base made of a semiconductor material having a pair of end faces, and a substrate having one or more protrusions extending between the end faces, and the surfaces of the substrate and the protrusions are covered with an active layer. Its thickness is inclined in the lateral direction (in the plane of the substrate surface, perpendicular to the axis of the protrusion). Above this active layer is a confinement layer.

The method for forming this laser includes the steps of depositing a layer of anti-corrosion material on a part of the substrate, etching the exposed portion of the surface of the substrate, and removing the anti-corrosion material to form the substrate surface Vc/substrate. The process includes a step of leaving a single layer, a step of further etching the surface to form a protrusion, and a step of sequentially depositing an active layer and a confinement layer on the surface of the substrate and the protrusion. .

The semiconductor laser 30 of FIG. 1 includes a semiconductor substrate 322 having parallel end faces 34, at least one of which is semi-transparent at the wavelength of the output laser beam, and a pair of side faces 36 extending between the end faces 34. Semiconductor body 32 includes a substrate 38 having a pair of opposing major surfaces 40,42.

The main surface 40 is covered with a buffer layer 44 having a circular protrusion 46 extending between the opposite end surfaces 34 of the base body 320 on its surface 48 . The ridges 46 and surface 48 of this buffer layer 44 are covered with an active layer 50 having a lateral VC thickness gradient. The active layer 50 is also covered by a confinement layer 52, which confinement layer 52 is in turn covered by an overcoat layer 54.
It is covered with This top coat layer 54 is formed by the protrusions 4 of the buffer layer 44.
an electrically insulating layer 56 extending over the opening in the form of a groove 58;
covered with The portion of the surface of the electrically insulating layer 56 and the surface of the overcoating layer 54 that corresponds to the groove 58 VC is covered with the first conductive layer 6o, and the second main surface 42 of the substrate 38 is covered with the second conductive layer 62. ing. This first and second conductive layer 60.62
Electrical contact is made to the first substrate 32.

Elements in the semiconductor laser 70 of FIG. 2 that are common to the semiconductor laser 30 of FIG. 1 are designated by the same reference numerals h.

The difference between this semiconductor laser ヮ0 and the semiconductor laser 30 is that
There is a pair of circular protrusions 46 on the substrate 38, and the buffer layer 44 covers the substrate and the protrusions. The active layer 50 is located on the buffer layer 44 and has a thickness equal to that of the protrusions 46.
The regions 92 between the two are inclined at the ± portions.

Substrate 38 is generally comprised of a binary [1-V compound composition or alloy, and has a surface 40 parallel to the (100) or (110) crystal planes. The substrate may deviate significantly from one of these orientations, but two or more are preferred, using the (100) or (110) planes. However, it should be understood that other substrate orientations may also be used. When choosing a substrate and each layer to be deposited on it, it is desirable that the crystal lattice of the layer matches that of the substrate. Further, it is preferable that the substrate is made of N-type INP.

Buffer layer 44 is generally made of the same material as the substrate and is used to provide a high quality surface upon which each layer can be deposited. This layer is generally about 3-10 microns thick. When the substrate 38 has a protrusion 46, the buffer layer is formed between the substrate 38 and the active layer 50.
It says to insert it in between.

The circular protrusions 46 in FIGS. 1 and 2 represent the buffer layer 4, respectively.
4 and the board 38. For example, the protrusion has a width of about 5 to 20 microns at its base and about 0.2 to 10 microns in height.

The height and width are chosen so that each layer deposited thereon has the desired curvature. The spacing between two or more protrusions and the height and width of each protrusion are selected so that each layer deposited thereon has the required curvature. Generally, the distance between the centers of both protrusions is about 10 to 10
It is 0μ.

The protrusions can be formed in the order shown in FIG. Third
In Figure (a), after depositing the buffer layer 104 on the substrate 102,
A mask layer 108 of a corrosion-resistant material such as polysilicon is deposited on a part of the surface 106 of the buffer layer 104 by a mark photoetching method. Etching is performed using an anisotropic etching solution such as a bromine methanol solution to etch the W barrier layer 104 cr) and the H peak portion to form a mesa 110 as shown in FIG. 3(b) on the surface 112 thereof. After that, the mask layer 108 is removed and the structure shown in FIG.
) leaving a mesa 110 and a surface 112. This/S1
10 and the surface 112 are further etched with the same or different etching solution to form the buffer layer 10 as shown in FIG. 3(d).
4 surface 122 K-circle-projection 120 is formed. An active layer, a confinement layer, and an overcoat layer are sequentially deposited over the ridges 120 and surface 122. It is clear that forming the ridges on the substrate itself and then applying each layer sequentially will also fail.

Each epitaxial layer on substrate 38 of FIG. 1 may be deposited using the liquid phase epitaxial method disclosed in U.S. Pat. No. 3,753,801, or U.S. Pat.
It can also be deposited using the vapor phase epitaxial method disclosed in No. 3. When using the method of Kojiro et al., the local growth rate of each layer changes with the local curvature of the generated surface, and the local growth rate increases as the positive local curvature increases, so it is possible to deposit layers with a gradient in thickness. can do.

The thickness of the active layer is generally about 0.05 to 2.2 microns, preferably about 0.1 to 0.5 microns. This layer may be undoped or slightly doped to VCP or uN type, for example, in the Journal of Electronic Materials (J
cstγnal of-Electronic Ma
terial) 1980 Vol. 9, p. 977, Olsen t'01sen:) As shown, the lattice almost coincides with the buffer layer, and the output luminous flux of the required wavelength can be obtained.
It may be constructed of InGaAsP or InGaAs, with the relative concentrations of each element chosen so that the

The confinement layer 52 is generally made of KP type InP and has a thickness of about 0.5 to 3 microns. Overcoat layer 54 may be used to improve the quality of electrical contact to laser 30;
Its thickness is typically about 0.2-0.5μ, and the confinement layer 52
InGaAsP”x, or InGaA of the same conductivity type as
Consists of s.

It should be understood that the device of the present invention can also be fabricated using other group II alloy combinations.

The electrically insulating layer 56 preferably comprises silicon dioxide deposited on the overcoat layer 38 by pyrolysis of a silicon-containing gas such as silane in oxygen or water vapor. The groove 58 is preferably formed using a standard photolithography method to reach the electrically insulating layer 561C and the overcoat layer 54, and when there is only one ridge 46, it is preferably provided in the soil of that ridge. When there are two twisted protrusions, a groove 58 is provided in the area between them.

Conductive layer 60 is preferably comprised of titanium, platinum and gold and is deposited by sequential vapor deposition. It will be obvious to those skilled in the art that in a device having only one protrusion 46, this conductive layer is sufficient to cover the portion of the confinement layer above the protrusion 46.

It is also possible to eliminate the electrically insulating layer 56 by depositing on the confinement layer 56 a blocking layer having a conductivity type opposite to that of t and a region having a region of the same conductivity type.

After this, a conductive layer 6o is applied to the entire surface of the blocking layer,
Bye. Applying a bias voltage to the laser 30 reverse biases the PN junction between the blocking layer and the confinement layer except for the regions of the confinement layer 52 that are converted to the same conductivity type.

Conductive layer 62 on second major surface 42 of substrate 38 may be formed by vacuum deposition and sintering of tin and gold.

The end face 34 of the laser 30 is typically coated with a layer such as aluminum oxide having a thickness of about % of the laser wavelength. This layer is described in US Pat. No. 4,178,564. Hey
The end face 34 facing the laser beam is coated with a mirror surface that reflects the laser wavelength, as described in U.S. Pat. Nos. 3,901,047 and 4,092,659.

FIG. 4 is a schematic enlarged view showing a microscopic image of a cross-section of a laser 150 constructed according to the principles of the present invention and having a desired slope, with a protrusion 154 [-] overlaid by a buffer layer of InP, and
It has an nP substrate 152. The surface of the buffer layer is approximately 30 mm thick
The active layer 156 of InGaAsP is covered with a confinement layer 158 of InP, and the confinement layer is covered with an overlayer 160 of InGaAsP.

Each layer can be identified by coloring methods known to those skilled in the art, but because the substrate 152 and the buffer layer are made of the same material and are similarly colored, their boundaries are difficult to discern. The protrusions 154 of the buffer layer are asymmetrical because the substrate surface is slightly deviated from the (110) direction force.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a semiconductor laser of the present invention, FIG. 2 is a sectional view of a second embodiment of the semiconductor laser of the invention, FIG. 3 is a sectional view showing each step of the method of the invention, and FIG. The figure is an enlarged view showing a cross section of the semiconductor laser of the present invention. 32... Base body, 34... End surface, 38... Substrate, 4
0.42...Opposing main surface, 46...Protrusion portion, 50...
Active layer, 52... - Confinement layer, 54. Overcoat layer, 60.
...first conductive layer, 62...second conductive layer. Patent ratio FA person Arun A Corporate Lane Yongyo
Rihito Tetsu Shimizu and 2 others Figure 3 Rod 4 Figure 54

Claims (2)

[Claims] (1) a semiconductor substrate having at least one semi-transparent two end surfaces, a substrate having opposing main surfaces, and a protrusion extending between the two end surfaces on one of the main surfaces, and covering the substrate; an active layer whose thickness slopes laterally from a portion covering the protrusion; and a confinement layer covering the active layer;
A first conductive layer covering a portion of the confinement layer above the ejection strip, and a second conductive layer covering a portion of the second main surface of the substrate.
1. the substrate has one conductivity type, the confinement layer and the overcoat layer have opposite conductivity types, and the active layer has a refractive index that is lower than the refractive index of the substrate and the confinement layer. Semiconductor laser characterized by high irradiance. (2) the substrate has a second protrusion substantially parallel to and spaced apart from the protrusion of the substrate, the thickness of the active layer being equal to or above the area between both protrusions of the substrate; A semiconductor laser according to claim 1, wherein the semiconductor laser is inclined from a portion.