JPH04257284A - Buried hetero structured semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser which suppresses leaking current from a p-type clad layer to an InGaAsP gain suppressing layer and that prevents the reduction of light output even when high current is injected by preventing the turn-on of a p-n-p-n current block part by the InGaAsP gain suppressing layer and providing a separating layer which has a structure that prevents the gain suppressing layer from directly making contact with an activating layer and a clad layer on a mesa stripe side. CONSTITUTION:A current block part is provided with a gain suppressing layer 5, whose forbidden band width is wider than an activating layer 3 and narrower than a buffer layer 2 and a clad layer 4, and a separating layer 9 which has a structure that prevents the gain suppressing layer 5 from directly making contact with the activating layer 3 and the clad layer 4 on a mesa stripe side.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buried heterostructure semiconductor laser in which a current blocking layer is provided to prevent current from flowing in regions other than the active layer.

0002

2. Description of the Related Art Buried heterostructure semiconductor lasers (hereinafter simply referred to as semiconductor lasers) are mainly used as light sources for optical fiber communications.

Next, the structure of a semiconductor laser according to the prior art will be explained with reference to FIG. In Figure 2, 1 is an n-type substrate, 2 is an n-type buffer layer, 3 is an active layer, and 4 is a p-type substrate whose polarity is opposite to that of substrate 1.
type cladding layer, 12 is a p-type current blocking layer, 6 is an n-type current blocking layer, 7 is a p-type buried layer, 8 is an electrode forming layer,
10 is an n-side electrode, and 11 is a p-side electrode.

In FIG. 2, a region other than the mesa stripe including the active layer 3 is connected to the active layer 3 in the opposite direction to form a current blocking layer 1 so that current flows efficiently through the active layer 3 of the light emitting section.
2 and 6 are formed to form a current block portion having a pnpn thyristor structure. However, the leakage current flowing from the p-type cladding layer 4 to the p-type current blocking layer 5 is p-n-p-
Since it acts as the gate current of the n current block section, during high current injection operation, the p-n-p-n current block section is turned on, and as a result, a large current flows through the entire current block section, resulting in the characteristics shown in Figure 4A. Become.

Next, the structure of another semiconductor laser according to the prior art will be explained with reference to FIG. FIG. 3 shows an improved version of the semiconductor laser shown in FIG. 5 in FIG. 3 is a gain suppression layer,
The rest is the same as FIG. 2. Since the gain suppression layer 5 has a forbidden band width wider than that of the active layer 3 and narrower than that of the current blocking layers 5 and 6, the sensitivity of the p-n-p-n current blocking portion to the gate current decreases, and turn-on occurs. It becomes difficult. However, since the forbidden band width of the gain suppression layer 5 is narrower than that of the p-type current blocking layer 12 in FIG. 2, the leakage current from the p-type cladding layer 4 becomes large, resulting in the characteristics shown in FIG. 4A.

[0006]

[Problems to be Solved by the Invention] In FIGS. 2 and 3, high output cannot be obtained because turn-on of the current block portion occurs and leakage current increases, respectively. This invention combines an InGaAsP gain suppression layer with an n-type buffer layer 2 and an n-type buffer layer 2.
By providing between the type current blocking layers 6, p-n-
InGaAsP gain suppression is achieved from the p-type cladding layer 4 by preventing turn-on of the p-n current blocking portion and providing an isolation layer with a structure in which the gain suppression layer does not directly touch the active layer 3 and the p-type cladding layer 4 on the side surface of the mesa stripe. The purpose of the present invention is to provide a semiconductor laser in which leakage current flowing through layers is suppressed and optical output does not decrease even when high current is injected.

[0007]

[Means for Solving the Problems] In order to achieve this object, in the present invention, a buffer layer 2 having the same polarity as the substrate 1, an active layer 3, and a cladding layer 4 having the opposite polarity to the substrate 1 are provided on the substrate 1. The area other than the mesa stripe including the active layer 3 is removed from the surface of the cladding layer 4 to a depth where the active layer 3 is separated, and the current blocking layer is bonded to this area in the opposite direction to the active layer 3 and grown. In the buried heterostructure semiconductor laser, there is a gain suppression layer 5 in the current block portion whose forbidden band width is wider than that of the active layer 3 and narrower than that of the buffer layer 2 and the cladding layer 4, and a gain suppression layer 5 on the side surface of the mesa stripe.
The isolation layer 9 has a structure that does not directly touch the active layer 3 and the cladding layer 4.

[0008]

[Operation] Next, the structure of the semiconductor laser according to the present invention will be explained with reference to FIG. Reference numeral 9 in FIG. 1 is an isolation layer, and the other parts are the same as in FIG. 3. Since the isolation layer 9 has a wider forbidden band width than the active layer 3 and has higher resistivity than the active layer 3 and the n-type buffer layer 2, most of the current flowing through the p-type cladding layer 4 passes through the active layer 3 to the n-type buffer layer. Only a small leakage current flows through the layer 2 and into the isolation layer 9.

During high current injection operation, current flowing from the p-type cladding layer 4 through the isolation layer 9 and the gain suppression layer 5 into the n-type buffer layer 2 flows through the p-type buried layer 7 and the n-type current blocking layer 6.
, a gain suppression layer 5, and an n-type buffer layer 2.
-Although it acts as a gate current of the pn thyristor structure, turn-on is suppressed by the presence of the gain suppression layer 5,
Prevent large current from flowing throughout the current block section. As a result, the semiconductor laser shown in FIG. 1 has the characteristics shown in FIG. 4C.

Next, a method for manufacturing the semiconductor laser shown in FIG. 1 will be explained. Let us take as an example a case where n-type InP is used as the semiconductor substrate material.

First, a flat (100) n-type InP substrate 1
On top, an n-type InP buffer layer 2 and an InGaAsP active layer 3
, p-type InP cladding layer 4 is sequentially grown.

Next, by a normal photolithography process, the active layer is etched in a mesa stripe shape in the <011> direction with a width of about 1 μm to a depth that divides the active layer. After growing an InP isolation layer 9 only on the sides of this mesa stripe,
An nGaAsP gain suppression layer 5, an n-type InP current blocking layer 6, a p-type InP buried layer 7, a p-type InGaAsP electrode forming layer 8 are grown, and finally electrodes 10 and 11 are formed.

[0013]

According to the present invention, the presence of the InGaAsP gain suppression layer 5 prevents turn-on of the p-n-p-n current blocking portion, and the presence of the InP isolation layer 9 prevents turn-on of the p-n-p-n current block portion.
Since the leakage current flowing from the p-type cladding layer 4 to the InGaAsP gain suppression layer 5 can be suppressed, a semiconductor laser whose optical output does not decrease even when a high current is injected can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a semiconductor laser according to the present invention.

FIG. 2 is a configuration diagram of a semiconductor laser according to the prior art.

FIG. 3 is a configuration diagram of another semiconductor laser according to the prior art.

FIG. 4 is a diagram showing optical output characteristics of a semiconductor laser.

[Explanation of symbols]

1 N-type substrate 2 N-type buffer layer 3 Active layer 4 P-type cladding layer 5 InGaAsP gain suppression layer 6 N-type current blocking layer 7 P-type buried layer 8 Electrode forming layer 9 Isolation layer 10 N-side electrode 11 p-side electrode 12 p-type current blocking layer

Claims (2)

[Claims] 1. On a substrate (1), a buffer layer (2) having the same polarity as the substrate (1), an active layer (3), and a substrate (
A cladding layer (4) with opposite polarity to 1) is sequentially grown, and the area other than the mesa stripe including the active layer (3) is removed from the surface of the cladding layer (4) to a depth where the active layer (3) is separated. In a semiconductor laser with a buried heterostructure in which a current blocking layer is grown in this part in a direction opposite to the active layer (3), the forbidden band width in the current blocking part is wider than that of the active layer (3), and the buffer layer (2) ,
a gain suppression layer (5) narrower than the cladding layer (4);
On the side of the mesa stripe, the gain suppression layer (5) is connected to the active layer (3).
), a buried heterostructure semiconductor laser comprising an isolation layer (9) having a structure that does not directly touch the cladding layer (4). 2. A buried heterostructure semiconductor laser according to claim 1, characterized in that the resistivity of the isolation layer (9) is higher than that of the cladding layer (4).