JPH05145192A - Semiconductor optical amplifier and manufacture thereof - Google Patents

Abstract

PURPOSE:To easily control the width of an active layer of a traveling wave type semiconductor optical amplifier having an oblique optical waveguide structure in which both side ends of a mesa of a semiconductor layer structure including a stripelike active layer are formed stepwisely. CONSTITUTION:When a side etching stepwise oblique optical waveguide structure is formed by using an SiO2 stripe mask 6 on an upper surface of a mesa, both side ends of an SiO2 stripe which are alternately formed stepwisely in directions [011] and [011] are used. Thus, when the side end of the mask 6 is etched in the direction [011] with bromoethanol, the surface A [111] is exposed in an inverted mesa shape, and the part in the direction [011] is exposed at the surface A [111] in a forward mesa shape. Thus, both the surfaces are exposed on the A surfaces [111], and hence scarcely side-etched, and the width of the active layer is determined according to the angle of a crystal at the [111] A surface and the width of the mask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical amplifier which amplifies light entering from an incident end and emits the amplified light from an emitting end.

[0002]

2. Description of the Related Art Semiconductor optical amplifiers are used as repeaters for optical communication. This semiconductor optical amplifier utilizes the same guided light amplification effect as a semiconductor laser. for that reason,
Reducing the light reflectance at the entrance end and the exit end is an important issue. That is, when there is a residual light reflectance, there is a problem that oscillation occurs when the light amplification factor is increased. In order to reduce this reflectance, a semiconductor optical amplifier having an oblique waveguide structure has been proposed in which an active layer is obliquely formed with respect to the end face at the same time as the low light reflecting films on the incident end face and the emission end face.

This oblique waveguide optical amplifier has, for example, as shown in FIG. 3, an n-type InP substrate 1 having a [100] plane and an n-type InP substrate 1.
The type InP buffer layer 2, the InGaAsP active layer 3, the p type InP clad layer 4, and the p type InGaAsP ohmic layer 5 are sequentially stacked. Next, a SiO ₂ film is deposited on the p-type InGaAsP ohmic layer 4. This SiO ₂ film is formed into stripes 6 having a slanting angle of about 7 degrees with respect to the [011] direction perpendicular to the end face by photolithography. Furthermore, S
Using the iO ₂ stripe 6 as a mask, the active layer is etched with bromine-methanol, and then the p-type InP layer 7, the n-type InP layer 8 and the n-type InGaAsP cap layer 9 are etched.
Embed by. Through these steps, the diagonal waveguide semiconductor optical amplifier is completed. After this, SiO ₂ stripe 6
Are removed, electrodes are provided on the surface of the p-type InGaAsP ohmic layer 5 and the back surface of the n-type InP substrate 1, and a low light reflection film is further formed on the end faces, and the chips are formed by cleavage.

[0004]

In the case of this oblique waveguide semiconductor optical amplifier, the side etching is large because the SiO ₂ stripe 5 is oblique with respect to the [011] direction. That is, when the stripes coincide with the [011] direction, side etching is less likely to occur because the [111] A surface, which is difficult to be etched, is exposed on the side surface of the mesa as the etching progresses. However, when the direction of the stripes deviates from [011], the side faces also [11]
1] Since it deviates from the A surface, it is easily etched. Since the side etching is large as described above, it becomes difficult to control the width of the active layer.

The present invention eliminates the above-mentioned drawbacks, and provides a semiconductor optical amplifier which can be manufactured easily and whose active layer width can be easily controlled.

[0006]

A semiconductor optical amplifier according to a first aspect of the present invention forms a mesa having a semiconductor layer structure including a stripe-shaped active layer that amplifies the intensity of light incident on a semiconductor substrate and emits the amplified light. In the traveling wave type semiconductor optical amplifier, the mesa including the stripe-shaped active layer is formed at both ends by a stepwise oblique waveguide.

In the method for manufacturing a semiconductor optical amplifier of the second invention, a SiO ₂ stripe mask is formed on the upper surface of the mesa of the semiconductor layer structure including the stripe-shaped active layer and side-etched to form a stepwise oblique optical waveguide structure. a process for preparing, both side ends of the SiO ₂ stripe mask 01
It is characterized in that the above-mentioned SiO ₂ stripe mask formed in a staircase pattern in which the [1] direction and the [01 ▲ bar ▼ 1] direction are alternately repeated is used.

[0008]

In the portion where the side edge of the SiO ₂ mask is in the [011] direction, the [111] A surface is exposed when etching with bromine-methanol to form an inverted mesa shape.
Similarly, in the direction of 1 bar 1], [11
1] Surface A is exposed to form a normal mesa shape. Both [11
1] Since the A surface is exposed, side etching is less likely to occur, and the active layer width is determined by the width of the SiO ₂ mask and the angle of the [111] A surface crystal. Therefore SiO
₂ The width of the active layer can be controlled only by the width of the mask.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.
c is for explaining the manufacturing process of the semiconductor optical amplifier of FIG. 1, and each drawing shows the intermediate production structure of the main process.

In FIG. 2A, first, an InP buffer layer 2, an InGaAsP active layer 3, a p-type InP clad layer 4, and a p-type InGaAsP ohmic layer are first formed on an n-type [100] InP substrate 1 by a liquid phase growth method or the like. 5 are sequentially grown. On the surface of the p-type InGaAsP ohmic layer 5, [0
11] and the [01 (1) bar 1] direction are repeated to provide a stripe-shaped SiO ₂ mask 6.

Subsequently, as shown in FIG. 2B, etching is performed to the bottom of the active layer 3 with bromine-methanol. In this case, the portion in the [011] direction has an inverted mesa shape, and the portion in the [01 (1) bar] direction has a forward mesa shape. for that reason,
At the intersection of the [011] direction and the [01 ▲ bar ▼ 1] direction, the side edge of the active layer is an oblique direction between [011] and [01 ▲ bar ▼ 1]. When the side edge of the active layer has a stepwise shape, the scattering loss becomes large with respect to the guided light, but since it is oblique at the intersection as described above, the loss can be suppressed to be small.

Finally, as shown in FIG. 2c, p-type InP layer 7, n-type InP layer 8 and n-type InGaAsP cap layer 9 are formed.
Then, the crystal growth process of the semiconductor optical amplifier is completed.

The above structure is characterized in that an oblique waveguide having a good controllability of the active layer width can be easily formed because side etching is small.

[0015]

As described in the above embodiments, the structure of the present invention makes it possible to obtain a semiconductor optical amplifier having a good controllability of the active layer width. Also, [011] and [01 ▲ bar ▼ 1]
The angle of the oblique waveguide and the like can be easily changed by adjusting the ratio of the length of the direction and the repetition period.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

2A, 2B, and 2C are perspective views for explaining a manufacturing process of the semiconductor optical amplifier of FIG.

FIG. 3 is a perspective view of a semiconductor optical amplifier having a conventional structure.

[Explanation of symbols]

1 substrate 2 buffer layer 3 active layer 4 clad layer 5 ohmic layer 6 SiO ₂ mask 7, 8, 9 buried layer 10 stepped SiO ₂ stripe mask formed on the mesa 11 both side ends of the mesa are formed stepwise Oblique optical waveguide structure

Claims (2)

[Claims] 1. A traveling-wave type semiconductor optical amplifier comprising a semiconductor layer structure mesa formed on a semiconductor substrate, the mesa having a stripe-shaped active layer for amplifying the intensity of incident light and emitting the amplified light. A semiconductor optical amplifier in which both ends of the mesa including the active layer are formed by stepwise oblique waveguides. 2. A method for producing a stepwise oblique optical waveguide structure by forming a SiO ₂ stripe mask on the upper surface of a mesa of the semiconductor layer structure including the stripe-shaped active layer and side-etching it according to claim 1. Both ends of the SiO ₂ stripe mask are in the [011] direction and the [01 ▲ bar ▼
1] The above-mentioned SiO formed in a step-like shape in which the directions are alternately repeated.
_A method for manufacturing a semiconductor optical amplifier, characterized by using a _two- stripe mask.