JPH0732278B2 - Semiconductor laser - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly, to a substrate having a circular ridge extending from one end (front end) to the other end (rear end) on the surface thereof. The present invention relates to a semiconductor laser including an active layer formed on a substrate.

[Conventional technology]

Semiconductor lasers generally consist of III-V compounds and include a body of semiconductor material having a thin active layer between two layers of opposite conductivity type. That is, there is a P-conductivity type layer on one side of the active layer and an N-conductivity type layer on the other side. Such semiconductor lasers typically emit laser light in more than one optical mode, which limits their use. U.S. Pat. No. 4,215,319 discloses a semiconductor laser which emits a stable single mode output light beam. The control of the output light beam from this semiconductor laser is performed by inclining the layer thickness. This semiconductor laser is constructed by depositing a confinement layer and a generation layer on a substrate having a pair of grooves substantially parallel to the surface, the inclination of which is obtained when each layer is formed by a liquid phase or vapor phase epitaxial method. It is caused by the difference in growth rate between the layer on the region between the two grooves and the layer on the groove.

However, when each layer is deposited on the indium phosphide substrate having such a pair of parallel grooves by using the liquid phase or vapor phase epitaxial method, the grooves are filled faster than the flat substrate portion and a continuous smooth surface is formed. Therefore, the surface of each layer becomes a flat plane. This growth habit of InP limits the utility of the structure of the US patent to lasers composed of InP and its related alloys. It is therefore desirable to have a laser of InP and its related alloys that exhibits the graded layer structure of the laser of the above-mentioned U.S. patent.

[Object of the Invention]

According to the present invention, by forming a circular ridge extending from one end to the other end on the surface of the substrate, the surface of the active layer formed on the substrate is curved to reduce the thickness of the active layer. An object of the present invention is to obtain a semiconductor laser capable of emitting an output light beam in a single optical mode with a required inclination.

[Outline of Invention]

The first semiconductor laser according to the present invention corresponds to the embodiment of FIG. 1 described later, and has a first main surface (for example,
40) and a bottom surface that becomes a second main surface (for example, 42), and a front end surface (for example, 34 on the front side in the figure) on which the laser beam is emitted, on the first main surface. A round ridge (for example, 34) that extends between the rear end surface on the opposite side (34 on the rear side in the figure)
It has a semiconductor body (eg 32) consisting of a substrate (eg 38) on which 46) is formed and an active layer (eg 50) formed over the first main surface of the substrate. This first
In the semiconductor laser described in (1), the active layer has a thickness that is relatively thin at the portion covering the top of the ridge, and on the inclined side portions on both sides of the top, the active layer gradually increases as it moves away from the top in the lateral direction. Is formed by.

The second semiconductor laser according to the present invention corresponds to the embodiment of FIG. 2 which will be described later, and has a first main surface (for example,
40) and a bottom surface that becomes a second main surface (for example, 42), and a front end surface (for example, 34 on the front side in the figure) on which the laser beam is emitted, on the first main surface. A substrate (eg, 38) formed with a pair of circular ridges (eg, 46, 46) extending substantially in parallel with the opposite rear end surface and spaced apart from each other by a predetermined distance; It has a semiconductor body (eg 32) comprising an active layer (eg 50) formed over the first major surface of the substrate. In this second semiconductor laser, the active layer has a relatively small thickness at the portion covering the central portion between the two ridge portions, and is closer to the ridge portions on both sides of the central portion than the central portion. It is formed in such a manner that it gradually increases as it goes.

In this semiconductor laser, for example, a step of depositing a mask layer of a corrosion resistant material on a part of the substrate, a step of etching an exposed portion of the surface of the substrate, and a mask layer of the corrosion resistant material are removed to form a mesa on the surface of the substrate. After the step of leaving, the step of further etching the surface to form a round ridge in the mesa, and the step of successively depositing an active layer and a confinement layer on the surface of the substrate and the ridge, Is generated.

[Explanation of Examples]

Hereinafter, the semiconductor laser of the present invention will be described in detail with reference to the drawings.

The semiconductor laser 30 shown in FIG. It includes a semiconductor body 32 having. In the embodiment of FIG. 1, the semiconductor body 32 comprises a first main surface (upper surface) 40 and a second main surface (upper surface) 40.
A substrate 38 having a main surface (bottom surface) 42, and a buffer layer (buffer layer) 44 formed to cover the first main surface of the substrate 38,
The active layer 50 is formed so as to cover the surface 48 of the buffer layer 44, and the confinement layer 52 is formed so as to cover the surface of the active layer 50. Although the buffer layer 44 is shown in the figure as a separate layer from the substrate 38, the buffer layer 44 can be considered in practice to be part of the substrate. The buffer layer 44 has on its surface 48 a circular ridge 46 extending between both end surfaces 34 of the semiconductor body 32, and the thickness of the active layer 50 formed so as to cover the surface of the buffer layer 44 is The portion covering the top of the ridge 46 is relatively thin, and gradually increases with increasing distance from the top on the inclined side portions on both sides of the top. The active layer 50 is covered with a confinement layer 52,
The confinement layer 52 is covered with an upper layer (cap layer) 54.

The upper layer 54 is covered with an electrically insulating layer 56 in which a groove-shaped opening 58 extending between both end faces 34 of the semiconductor body 32 is formed in a portion of the buffer layer 44 that abuts the protrusion 46. The surface of the electrically insulating layer 56 and the portion of the upper layer 54 exposed in the groove-shaped opening 58 are the first conductive layer.
Covered with 60, the second major surface 42 of the substrate 38 has a second conductive layer 62.
Is covered with. The first conductive layer 60 acts as the first electrode of the semiconductor laser, and the second conductive layer 62 acts as the second electrode.

In the semiconductor laser having the above structure, the thickness of the ridge 46 is increased by making the ridge 46 round, in particular, as compared with the buffer layer or the substrate having the ridge of a square or trapezoid. The laterally escalating active layer 50 away from can be easily shaped as desired, so that a single mode laser beam can be emitted with greater stability.

FIG. 2 shows the structure of the second embodiment of the semiconductor laser of the present invention.

In the semiconductor laser 70 of FIG. 2, the semiconductor laser of FIG.
Elements in common with 30 are designated with the same reference numbers. This semiconductor laser 70 is different from the semiconductor laser 30 of FIG. 1 in that a pair of circular ridges 46 is formed on a substrate 38, and the buffer layer 44 is formed between the substrate 38 and the ridges 46, 46. It is covering. An active layer 50 is formed on the buffer layer 44, and the thickness of the active layer 50 is relatively thin on the central part of the region 72 between the two ridges 46, 46 and on the central part of the region 72. Is relatively thicker as it approaches the ridges 46, 46.

Substrate 38 typically comprises a binary III-V compound or alloy and has a first major surface parallel to the (100) or (110) crystal plane.
Having 40. Substrate 38 may be slightly offset from one of these orientations, but it is preferred to use plane (100) or (110). However, it should be understood that other substrate orientations may be used. When selecting the substrate 38 and each layer to be deposited thereon, it is desirable that the crystal lattice of each layer be matched with that of the substrate 38. The substrate 38 is preferably made of N-type InP.

The buffer layer 44 is generally made of the same material as the substrate 38 and is used to form a high quality surface upon which each layer can be deposited. The buffer layer 44 is typically about 3-10 .mu.m thick. When the protrusions 46 are formed on the substrate 38, the buffer layer
The 44 may be inserted between the substrate 38 and the active layer 50.

In the semiconductor laser shown in FIG. 2, the round ridges 46, 46 are buffer layers 44.
However, the buffer layer 44 can be regarded as a part of the substrate 38 as in the semiconductor laser of FIG. The ridges 46, 46 have, for example, a width of about 5 to 20 [mu] at their base and a height of about 0.2 to 10 [mu]. The height and width are chosen so that each layer deposited on it has the required curvature. If there are more than two ridges, the spacing, height and width of each ridge is chosen so that each layer deposited thereon has the required curvature.
Generally, the distance between the centers of the two protrusions 46, 46 is about 10 to 100 μ.
Is.

The ridges 46, 46 can be formed in the order shown in FIG. In FIG. 3 (a), after the buffer layer 104 is deposited on the substrate 102, a mask layer 108 of a corrosion resistant material such as silicon oxide is coated on a part of the surface 106 of the buffer layer 104 by a standard photo-etching method. Then, the surface 106 is etched with an anisotropic etching solution such as a 0.1 to 1.0% bromine methanol solution to etch the exposed portion of the buffer layer 104, and the surface 112 is exposed to the surface 112 as shown in FIG. 3 (b). Forming a mesa 110. After that mask layer 108
Are removed to leave the mesa 110 and the surface 112 as shown in FIG. 3 (c). The mesa 110 and the surface 112 are further etched with the same or different etching solution, and as shown in FIG. 3 (d), the protrusion 122 having a round cross section is projected on the surface 122 of the buffer layer 104.
0 and 120 are formed. An active layer, a confinement layer and an overlayer are sequentially deposited on the ridge 120 and the surface 122. It is obvious that the same effect can be obtained by forming the ridges on the substrate itself and then sequentially applying the layers.

Each epitaxial layer on the substrate 38 of FIG.
The liquid phase epitaxial method disclosed in 3753801 may be used for the deposition, or the vapor phase epitaxial method disclosed in US Pat. No. 4,116,733 may be used for the deposition. Using these methods, the local growth rate of each layer changes with the local curvature of the surface on which it is generated, and the local growth rate increases as the positive local curvature increases, so that a layer with a gradually changing thickness is deposited. can do.

The thickness of the active layer is generally about 0.05-2.2μ, preferably about 0.1.
~ 0.5μ. This active layer is undoped or slightly P-type or N-type doped, for example the Journal of Electronic Materials (Journal of E
As disclosed in Olsen's paper, Vol. 9, 1980, vol. 9, p. 977, the relative concentration of each element is such that the lattice is almost the same as that of the buffer layer and the output light beam of the required wavelength is obtained. May be composed of InGaAsP or InGaAs selected.

The confinement layer 52 is typically made of P-type InP and has a thickness of about 0.5-3.
is μ. The overlayer 54 may be used to improve the electrical contact of the electrodes to the semiconductor laser 30.
Its thickness is usually about 0.2 to 0.5 μ and is made of InGaAsP or InGaAs of the same conductivity type as the confinement layer 52.

It should be understood that the device of the present invention can be made using other III-V alloy combinations.

The electrically insulating layer 56 preferably comprises silicon dioxide deposited on the overlayer 54 by thermal decomposition of a silicon-containing gas such as silane in oxygen or water vapor. The groove openings 58 are overcoated on the electrically insulating layer 56 using standard photo-etching techniques.
Formed until reaching 54. As shown in Fig. 1, the ridge portion
When there is one 46, it is preferable to provide a groove-shaped opening on the protrusion. Further, as shown in FIG. 2, when there are two ridges, a groove-shaped opening 58 is provided on the region 72 between them.

The first conductive layer 60, which serves as the first electrode of the semiconductor laser, is preferably made of titanium, platinum and gold and is deposited by sequential vapor deposition. It is apparent to those skilled in the art that this conductive layer is sufficient for a semiconductor laser having one ridge 46 to cover the confinement layer above the ridge.

It is also possible to dispense with the electrically insulating layer 56 by depositing a blocking layer on the confinement layer 52 with an opposite conductivity type and partly with a region of the same conductivity type. After that, the conductive layer 60 may be deposited on the entire surface of the blocking layer. When a bias voltage is applied to a semiconductor laser having a blocking layer, the PN junction between the blocking layer and the confinement layer 52 is reverse biased except for the region of the confinement layer 52 that has been converted to the same conductivity type.

The second conductive layer 62 on the second major surface 42 of the substrate 38 acts as the second electrode of the semiconductor laser, which can be formed by vacuum deposition and sintering of tin and gold. .

The front end face 34 of the semiconductor laser 30 is usually coated with a layer of aluminum oxide or the like having a thickness of about ½ of the laser wavelength. This layer is described in US Pat. No. 4,178,564. The rear end surface 34 facing this is coated with a mirror surface that reflects laser wavelength light, which is described in U.S. Pat. Nos. 3,710,047 and 4092659.
No.

FIG. 4 is a model enlarged view showing a microscope image of a cross section of a semiconductor laser 150 having a required inclination, which is constructed according to the principle of the present invention, and an InP substrate 152 covered with an InP buffer layer having a ridge 154. Have. The surface of the buffer layer is InGaAs with a thickness of about 300 nm.
The active layer 156 is covered with a P active layer 156, and the active layer 156 is an InP confinement layer.
158, whose confinement layer 158 is an InGaAsP overlayer 160.
Is covered with. Although each layer can be identified by a coloring method known to those skilled in the art, the boundary line cannot be identified because the substrate 152 and the buffer layer are made of the same material and are similarly colored. The ridges 154 of the buffer layer are asymmetric because the substrate surface is slightly deviated from the (110) direction.

〔The invention's effect〕

As described above, according to the present invention, since the round protrusion 46 is formed on the substrate or the buffer layer, the active layer 50 formed on the protrusion 46 has a thickness from the top of the protrusion. High stability because it can be easily formed laterally toward the side of the ridge or laterally toward the side of the ridge from the central region between the two ridges. A semiconductor laser capable of emitting a single-mode laser beam can be obtained.

[Brief description of drawings]

1 is a perspective view showing the structure of the main part of the first embodiment of the semiconductor laser of the present invention, and FIG. 2 is a front view showing the structure of the main part of the second embodiment of the semiconductor laser of the present invention. FIG. 3 is a schematic sectional view showing each step of a method for forming a round protrusion of a semiconductor laser of the present invention, and FIG. 4 is an enlarged view showing a section of the semiconductor laser of the present invention. 30 ... Semiconductor laser (first embodiment), 32 ... Semiconductor body, 34 ... End surface, 36 ... Side surface, 38 ... Substrate, 40 ... First
Main surface, 42 …… second main surface, 46 …… projection, 48 ……
Surface, 50 ... Active layer, 52 ... Confinement layer, 54 ... Overlayer, 56 ... Insulating layer, 58 ... Groove-like opening, 60 ... First conductive layer, 62 ... Second Conductive layer, 70 ... Semiconductor laser (second
Example).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Thomas Ziosef Zamerowski 336 Yderley Robin Hood Drive, Pennsylvania, United States 336 (56) Reference JP-A-51-114887 (JP, A) Kai 54-152879 (JP, A) JP 56-46593 (JP, A) JP 54-32284 (JP, A) JP 56-61190 (JP, A)

Claims (4)

[Claims] 1. A rear end surface opposite to a front end surface from which laser light is emitted, having a top surface serving as a first main surface and a bottom surface serving as a second main surface. And a substrate formed with a circular ridge extending between the substrate and the first main surface of the substrate and having a thickness that is relatively thin at the portion that covers the top of the ridge. An active layer that gradually increases laterally away from the top on the sloping sides of the top,
A semiconductor body comprising a confinement layer formed to cover an upper surface of the active layer, and a semiconductor body formed to cover at least a portion of the upper surface of the confinement layer immediately above the ridge. A first conductive layer forming an electrode of, and a second conductive layer forming a second electrode for the semiconductor body, the second conductive layer being formed so as to cover the second main surface of the substrate. At least the front end face of the main body from which the laser light is emitted is semi-transparent at the wavelength of the laser light, the substrate has a first conductivity type, and the confinement layer has a conductivity type opposite to that of the substrate. A semiconductor laser having a second conductivity type, wherein the active layer has a refractive index higher than those of the substrate and the confinement layer. 2. An upper cover layer is formed to cover the confinement layer, an electric insulating layer is formed to cover the upper cover layer, and an opening is formed through the electric insulating layer. The semiconductor laser according to claim 1, wherein the first conductive layer is formed so as to cover the upper layer in the opening formed in the electrically insulating layer. 3. A rear end surface opposite to a front end surface from which laser light is emitted, which has an upper surface serving as a first main surface and a bottom surface serving as a second main surface. And two circular ridges extending between the substrate and the substrate are formed so as to be substantially parallel to each other and separated from each other by a predetermined distance, and cover the first main surface of the substrate. An active layer having a thickness that is relatively thin at a portion covering a central portion between the two protruding portions, and gradually increases toward the protruding portions on both sides of the active portion, and an upper surface of the active layer. A semiconductor body formed of a confinement layer formed to cover the upper surface of the confinement layer, and a portion of the upper surface of the confinement layer that covers at least a portion directly above the central portion between the two ridges.
A first conductive layer forming a first electrode for the semiconductor body, and a second conductive layer formed to cover a second main surface of the substrate and forming a second electrode for the semiconductor body. And at least a front end face of the semiconductor body from which the laser light is emitted is semi-transparent at a wavelength of the laser light, the substrate has a first conductivity type, and the confinement layer is the substrate. A semiconductor laser having a second conductivity type opposite to that of, wherein the refractive index of the active layer is greater than the refractive indices of the substrate and confinement layer. 4. An upper cover layer is formed to cover the confinement layer, and an electric insulating layer is formed to cover the upper cover layer, and the electric insulating layer is formed on a region between the ridge portions. An opening penetrating a portion is formed, and the first conductive layer is formed so as to cover the upper cover layer in the opening formed in the electrically insulating layer.
The semiconductor laser described.