JPH03263890A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To achieve oscillation at a low threshold current and obtain a fine light output in a minimum order horizontal mode by providing an activation layer between two stripe-shaped mesas with a sharp peak part which is provided by etching a semiconductor substrate and by providing a current blocking layer on the outside. CONSTITUTION:A resist pattern 12 is formed in a position where a stripe-shaped mesa 2 is left on a surface of an N-type InP substrate 1 and a strip-shaped mesa 2 with a sharp peak part is formed by etching, thus forming peak parts 4 and a groove part which is sandwiched by the peak parts 4. After eliminating the resist pattern 12, an N-type InP layer 5, an InGaAsP layer 6, and a P-type InP layer 7 are formed only in a region other than the peak parts and an N-type InP layer 8 is formed only at a region excluding the groove part 3 and the peak parts 4 of the stripe-shaped mesa 2. Then, a P-type InGaAs layer 9 which becomes a contact layer is formed uniformly over the entire surface, thus forming a P-side electrode 10 and an N-side electrode 11.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser device that operates at room temperature and is used as a light source for optical communication or optical recording, and a method for manufacturing the same.

Conventional technology Semiconductor laser devices can operate at room temperature by using a heterojunction, and also have a buried structure in which the active layer is surrounded by a semiconductor crystal thin film with a larger energy gap (and lower refractive index) than the active layer. This makes it possible to operate at low currents and obtain clean laser output in the lowest-order transverse mode.This type of semiconductor laser device is a buried heterojunction diode laser (hereinafter referred to as BH).
It is called a laser.

A conventional semiconductor laser device will be described below using a BH laser as an example.

FIG. 3 is a cross-sectional view of a conventional BH laser.

A conventional BH laser has an N-type 1nP substrate 30 and an N-type 1nP substrate 30.
An nP layer 31 is formed, a striped mesa 32 is formed in a part of the nP layer 31, and an rnGaAsP layer 33 and a P-type 1nP layer 34 are formed on the striped mesa 32 to form a heterojunction. Then, the P-type 1nP layer constituting the blocking layer 3 surrounding the InGaAsP layer 33
A layer 35 and an N-type 1nP layer 36 are formed, and a P-type 1nP layer 37 is formed on the entire striped mesa 32 as well.
A P-type InGaAsP layer 38 is formed. BH
A P-side electrode 39 and an N-side electrode 40 are formed on both sides of the laser, respectively.

The method for manufacturing a BH laser with such a structure will be explained below, and can be broadly divided into a first step of forming a double heterojunction including an active layer, and a second step of forming a current blocking layer for confining current. It consists of.

As a first step, an N-type InP layer 31, an InGaAsP layer 33, and a 3-nP layer 34 are sequentially grown by liquid crystal epitaxial growth on the surface of an N-type 1n, P substrate 30 to form a double heterojunction. Thereafter, unnecessary parts are etched to form a striped mesa 32 with an active layer on top. Next, as a second step, a P-type InP layer 35 and an N-type 1nP layer are formed in a region other than the striped mesa 32.
Form layer 36. Thereafter, a P-type 1nP layer 37 and a P-type InGaAsP layer 38 are formed on the entire surface. Furthermore, P
A BH laser is manufactured by forming a P-side electrode 39 on the type 1nGaAsP layer 38 and an N-side electrode 40 on the inP substrate 30 side.

Problems to be Solved by the Invention However, in the conventional configuration described above, the active layer has a uniform thickness, which causes confinement of laser light, making it difficult to obtain desirable low-order transverse mode characteristics, and reducing the current threshold. In addition to problems such as things that cannot be done, it was necessary to perform epitaxial growth twice.

The present invention solves the above-mentioned conventional problems, and aims to provide a semiconductor laser device that oscillates with a low threshold current and provides a clear optical output in the lowest order transverse mode, and a method for manufacturing the same.

Means for Solving the Problems In order to achieve this object, the semiconductor laser device of the present invention provides an active layer between two striped mesas each having a sharp top formed by etching a semiconductor substrate. It has a structure with a current blocking layer on the outside,
The active layer and the current blocking layer are formed by one epitaxial growth.

Effect This configuration not only improves luminous efficiency, but also allows the growth rate of concave portions of the semiconductor substrate to be faster than convex portions in the epitaxial growth method.If the degree of supersaturation of the source solution used for crystal growth is low, sharp peaks can be formed. This makes it possible to take advantage of the phenomenon that crystal growth does not occur on the mesas that are present.

EXAMPLE Hereinafter, an example of the present invention will be described using a BH laser as an example with reference to the drawings.

FIG. 1 is a sectional view of a BH laser according to an embodiment of the present invention, and FIGS. 2(a) to 2(h) are sectional views of the same process.

In FIG. 1, 1 is an N-type InP substrate, 2 is a striped mesa, 3 is a groove surrounded by two striped mesas 2, 4 is the top of the striped mesa 2, 5 is an N-type 1nP layer,
6 is InGaAsP layer, 7 is P type 1nP layer, 8 is N type 1
nP layer, 9 is a P-type InGaAsp layer, 10 is a P-side electrode,
11 is an N-side electrode.

Regarding the BH laser configured as above, the following is the first part.
The operation will be explained according to the diagram.

An N-type 1nP layer 5 formed in the groove 3 sandwiched between the striped mesas 2, an InGaAsP layer 6 serving as an active layer, and a P
The 1nP type layer 7 becomes the active layer, and the N-type 1nP layer 5 and the InGaAs active layer are formed around the striped mesa 2.
The P layer 6, the P type 1nP layer 7, and the N type 1nP layer 8 form a current blocking layer by forming a silicon risk. Therefore, the current is confined in the active layer formed in the grooves 3 between the striped mesas 2. In addition, since the InGaAsP layer 6, which serves as the active layer, is thick at the center and thin at both ends, the laser light is confined, providing desirable transverse mode characteristics and preventing optical loss, making it possible to lower the current threshold. Ru.

Next, a method for manufacturing a BH laser according to an embodiment of the present invention will be explained along the process cross-sectional views of FIGS. 2+'a) to (W).

As shown in FIG. 2(a), a resist pattern 12 is formed on the surface of the N-type 1nP substrate 1 at a position where the striped mesa 2 is left, and hydrochloric acid (HCI), phosphoric acid (83PO4) and hydrogen peroxide (H202) are applied to the resist pattern 12. By etching the N-type InP substrate 1 using the mixed etching solution, the etching process shown in the same figure (
A striped mesa 2 with a sharp top is formed as shown in b'). As the etching of the N-type InP substrate 1 progresses, the etched region becomes the resist pattern 12.
Therefore, by setting the radius and spacing of the resist pattern 12 to appropriate values and adjusting the etching time, grooves 3 sandwiched between the top portions 4 and the top portions 4 are formed at intervals of 2 to 3 μm. . After removing the resist pattern 12, each semiconductor crystal thin film is sequentially formed by liquid phase epitaxial method.

In general, in the liquid phase epitaxial method, a semiconductor crystal thin film grows faster on a concave portion than on a convex portion of a semiconductor substrate, and if the supersaturation degree of the source solution used for crystal growth is small, crystal growth will occur on a mesa with a sharp top. is known not to occur. By utilizing this property, the first
As shown in Figure (C), N-type I is applied only to the area other than the top 4.
An nP layer 5 can be formed. Similarly, the InGaAsP layer 6 shown in the same figure (d) and the P-type 1nP layer shown in the same figure (e)
A layer 7 is formed in areas other than the top 4. Furthermore, the growth rate of the semiconductor crystal thin film within the groove portion 3 having a width of 2 to 3 μm is faster than that in the peripheral region. Therefore, if the growth time of each semiconductor crystal thin film is adjusted so that the groove 3 is almost buried when the P-type 1nP layer 7 is formed, the surface of the P-type 1nP layer 7 in the groove 3 will have a gradual recess. is formed. Therefore, by adjusting the supersaturation degree of the solution for forming the semiconductor crystal thin film, N-type lnP
The layer 8 can be grown only in the regions of the striped mesa 2 excluding the grooves 3 and the tops 4. Next, as shown in the figure (g), a P-type InGaAsP layer 9 that will become a contact layer is uniformly formed over the entire surface, and a P-side electrode 10 and an N-side electrode 11 are formed as shown in the figure (h). do.

In the above description, an N-type semiconductor substrate was used and an example was shown in which a combination of InP and InGaAsP was used.
It is also possible to fabricate a P-type semiconductor substrate by changing the conductivity type of each semiconductor crystal thin film. In addition, other combinations of semiconductor materials for forming heterojunctions can be similarly manufactured.

Effects of the Invention As described above, the present invention has a structure in which an active layer is formed between two striped mesas having sharp tops provided on a semiconductor substrate, and a current blocking layer is formed outside the active layer. It is possible to realize an excellent semiconductor laser device that oscillates with a low current threshold and emits clean laser light in the lowest order transverse mode, and an excellent manufacturing method that can manufacture the semiconductor laser device by one epitaxial growth.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a BH laser according to an embodiment of the present invention, Figures 2 (a) to (W are cross-sectional views of the manufacturing process of the same BH laser, and Figure 3 is a cross-sectional view of a conventional BH laser). 1... N-type 1nP substrate (semiconductor substrate), 2...
...Stripe mesa, 3...Groove, 4.
...top, 5...N-type 1nP layer (first layer), 6...1nGaAsP layer (second layer), 7...
...P-type 1nP layer (third layer), 8...N-type rnP layer (fourth layer), 9...P-type InGaAs
P layer (fifth layer'), 10.11-----electrode.

Claims (4)

[Claims] (1) Two striped mesas having sharp tops are provided on a semiconductor substrate of one conductivity type, and a first layer of one conductivity type, a second layer serving as an active layer, and A third layer of opposite conductivity type is sequentially provided, a fourth layer of one conductivity type is provided in a region other than the top portion and the groove between the striped mesas, and a fourth layer of one conductivity type is provided on the third layer and the fourth layer. A semiconductor laser device, wherein a fifth layer of opposite conductivity type is provided on the entire surface, and electrodes are provided on the semiconductor substrate and the fifth layer, respectively. (2) The material constituting the semiconductor substrate, the first layer, the third layer, and the fourth layer is indium phosphide (InP), and the material constituting the second layer and the fifth layer is indium gallium arsenide phosphide (InP).
2. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is GaAsP. (3) A step of etching a semiconductor substrate of one conductivity type to form two striped mesas having sharp tops, and forming a first layer and an active layer of one conductivity type on the semiconductor substrate excluding the tops. a step of sequentially forming a second layer and a third layer of opposite conductivity type by an epitaxial growth method; and a step of forming a fourth layer of one conductivity type by an epitaxial growth method in a region other than the top portion and the groove portion sandwiched between the striped mesas. a step of forming a fifth layer of opposite conductivity type on the entire surface of the third layer and the fourth layer by epitaxial growth;
A method for manufacturing a semiconductor laser device, further comprising the step of providing electrodes on the semiconductor substrate and the fifth layer, respectively. (4) The material constituting the semiconductor substrate, the first layer, the third layer, and the fourth layer is indium phosphide (InP), and the material constituting the second layer and the fifth layer is indium gallium arsenide phosphide (InP).
4. The method for manufacturing a semiconductor laser device according to claim 3, wherein the semiconductor laser device is made of GaAsP.