JPS63169087A - 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 "Field of Industrial Application" The present invention relates to a semiconductor laser having a current confinement structure suitable for use in optical communications and the like.

"Prior Art" Semiconductor lasers are widely used in fields such as optical communications, and various structures are used. In this case, there are n-type and p-type substrates for semiconductor lasers, and a conventional method for manufacturing a semiconductor laser using a p-type substrate will be described with reference to FIG. Note that FIG. 3 is a cross-sectional view of the embedded semiconductor laser taken along a plane perpendicular to the optical axis.

First, as the first growth step, 4′ shown in FIG.
A p-InP buffer layer 2, an undoped InGaAsP active layer 3, and an n-InP cladding layer 4 are sequentially epitaxially grown on a p-type substrate l as shown in FIG.

Next, a mask such as 5i02 is applied to the top surface of the n-InP cladding layer in the optical axis direction, and then an inverted mesa-like etching process is performed as shown in the same figure (b) to form long stripes in the optical axis direction. Furthermore, in order to narrow the width of the active layer 3, selective etching is performed to slightly etch only the active layer 3.

Then, as a second growth step, as shown in FIG. Embed striped structure.

"Problems to be Solved by the Invention" By the way, in manufacturing the above-described conventional p-type substrate semiconductor device, there were the following drawbacks.

■There are the following three conditions for creating a device, but it is extremely difficult to create a device while satisfying all of these conditions at the same time.

(a) The n-1nP buried layer 6 should be as thick as possible (1 μm or more).

(b) The n-1nP buried layer 6 is the n-InP cladding layer 4
must not be connected to In other words, the n-1nP buried layer 6 rises too much on the side surface of the stripe structure and becomes n-1nP.
It must not touch the P cladding layer 4.

(c) In order to satisfy both conditions (a) and (b) above, it is necessary to widen the width of the stripe structure, but even in this case, the width of the active layer 3 must not be widened.

■ After reverse mesa edge blowing to create a stripe structure, selective etching is performed to narrow the active layer width, but at this time a void is created beside the active layer, and this void is filled with n- 1nP melt enters and good buried growth cannot be achieved.

For this reason, leakage current could not be suppressed sufficiently, resulting in a problem with the accuracy of device characteristics.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a semiconductor laser that is easy to manufacture, allows for good buried growth, and improves device characteristics.

Means for Solving Problem F J In order to solve the two-legged problem, the present invention provides a semiconductor substrate of a first conductivity type, in which a convex stripe long in the optical axis direction is provided at the center of the upper surface; For example, with a p-InP substrate, an n
a second conductivity type current blocking layer made of -1nP or n-I nGaAsP; a first p-1nP layer provided on the current blocking layer and the entire upper surface of each of the stripes; an undoped InGaAsP active waveguide layer with a selectively narrowed width provided elongated in the optical axis direction at a position corresponding to above the stripe on the upper surface; an n-1 nP cladding layer that is wide and long in the optical axis direction, for example, in the shape of an inverted mesa;
The active waveguide layer and the surface area n-
A second p-
an InP layer, and an n-layer which is provided on the top surface of this second p-1nP layer and embeds both upper sides of the n-1nP cladding layer.
It has a 1nGaAsP layer.

"Function" The width of the active waveguide layer is adjusted by selective etching regardless of other conditions, and the first p-InP layer is interposed between the top and bottom of the device, and the n-InP cladding and the n1nP current Prevent contact between blocking layers.

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

FIG. 1 is a cross-sectional view showing the structure of an embodiment of the present invention. In the figure, 10 is a p-InP substrate, and a convex stripe IOa long in the optical axis direction is provided at the center of the upper surface of the substrate. 11 is a stripe IO on the top surface of the substrate 10
n-1nP (or n
-1nGaAsP) current blocking layer, I2 is a p-InP layer provided on the current blocking layer Il and the upper surface of the stripe loa, 15 is the upper surface of the p-1nP layer and is placed in the optical axis direction at a position corresponding to above the stripe 10a. An undoped InGaA sP active waveguide layer 16 is provided elongated in the optical axis direction on the upper surface of the active waveguide layer I5.

Further, I3 is a p-1nP layer provided on the p-InPnP2O5 surface and covers both sides of the lower part of the active waveguide layer 15 and the n-1nP cladding layer 16, and 14 is a p-1nP layer provided on the upper surface of the 1)-InP layer and 1+ This is an n-1n GaAsP layer covering both sides of the top of the -1nP cladding layer 16.

Next, a manufacturing method of this embodiment with the above configuration will be explained.

First, as shown in FIG. 2(a), convex stripes 10a are formed on the substrate IO by photolithography or the like. After that, as the current blocking layer 11, n-1nP (
Alternatively, n-InGaAsP) is selectively grown so that the upper surface of this current blocking layer 11 and the upper surface of the stripe IOa are uniform. And p-InP layer 12
, InGaAsP active waveguide layer 15 and n-1nl'
The cladding layer 16 is sequentially grown epitaxially as shown in the same figure (
A laminated structure as shown in b) is formed. In addition, p-In
By performing a melt-back process before growing the P layer 12, the surface beneath it becomes flat.

Next, a long (SiOx film, etc.) is attached to the center of the upper surface of the n-1nP cladding layer 16 in the optical axis direction, and reverse mesa etching is performed to form an inverted mesa shape as shown in FIG. The etching in this case is a selective etching, and p-I
Etching should be stopped at the nPnP2O5 surface. Furthermore, in order to make only the InGaAsP active waveguide layer 15 thinner, only this layer is selectively etched to make it narrower than the lower surface of the n-1nP cladding layer 16, as shown in the figure.

In this case, the width of the active waveguide layer 15 can be adjusted independently of the mesa shape in order to perform selective etching.

Next, as shown in FIG. 2(d), a p-rnP layer 13 is epitaxially grown on the upper surface of the p-1nP layer 12 to near the center of the n-InP cladding layer 16.
An n-InGaAsP layer I4 is grown on the top surface of the -1nP layer 13 to bury the InGaAsP active waveguide layer 15 and cladding layer 16. The above processing procedure completes the manufacturing process of this example.

Note that the above embodiment was an example in which a p-1nP substrate was used, but instead of this, a second conductivity type, that is, an nP substrate was used.
A type substrate may be used, and a GaAs-based semiconductor other than an InP-based semiconductor may be used.

"Effects of the Invention" As explained above, according to the present invention, there is provided a semiconductor substrate of a first conductivity type in which a protrusion extending in the light emission direction is formed in the center of the upper surface, and a semiconductor substrate of the first conductivity type. Since the current blocking layer of the second conductivity type is formed on the upper surface of the ridge and on both sides of the protrusion, the following advantages can be obtained.

■The n-1nP (or n-I nGaAsP) current blocking layer 11 corresponds to the n-1nP layer 6 shown in FIG.
1 can be arbitrarily set irrespective of other constituent elements, and the current blocking effect can be increased.

(2) Since the first p-InP layer partitions the upper and lower layers of the device, the n-1nP current blocking layer and the n-InP cladding layer are not connected.

(2) The width of the active waveguide layer can be easily adjusted by selective etching regardless of other conditions.

(2) Since the n-1nP current blocking layer is grown first, n-InP does not grow on the side surfaces of the active waveguide layer.

By obtaining the advantages (1) to (4) above, leakage current can be sufficiently suppressed, and a semiconductor laser with high optical output and low threshold current can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the manufacturing method of the same embodiment, and FIG. 3 is for explaining a conventional semiconductor laser and its manufacturing method. FIG. IO...p-1nP board, loa...
Stripe, 11... n-1nP'i style block layer, 12... first p-1nP layer, 13...
...Second p-1nP layer, 14-- n -I n
GaA sP layer, I5-...-1nGaA sP
Active waveguide layer, 16...n-1nP cladding layer.

Claims (1)

[Claims] a first conductivity type semiconductor substrate having a protrusion extending in the light emission direction formed in the center of the upper surface; and a second conductivity type semiconductor substrate having a second conductivity type semiconductor substrate formed on the upper surface of the first conductivity type semiconductor substrate on both sides of the protrusion. 1. A semiconductor laser comprising a conductive current blocking layer.