JPH05299771A - Semiconductor laser diode - Google Patents

Abstract

PURPOSE:To reduce a leak current outside a light emitting region, and to enable the laser to stably operate at a high temperature and high output ranges by increasing a parasitic turn-on voltage of a thyristor that occurs in a current block section in a semiconductor laser having a buried structure. CONSTITUTION:An n-type buffer layer 2, an active layer 3, and a cladding layer 4 are grown on an n-type semiconductor substrate 1, and mesa stripes are formed by selective etching. A p-type current block layer and an n-type current block layer 7 are then formed. Thereafter, a p-type buried layer 8 and a cap layer 9 are formed, whereby a laser diode is manufactured. In such a laser diode, the p-type current block layer is formed into a double-layer structure that is made up of a low-carrier-concentration current block lower layer 5 and a high-carrier-concentration current block upper layer 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser diode, and more particularly to a buried structure type semiconductor laser diode.

[0002]

2. Description of the Related Art FIG. 2 is a sectional view showing an example of a conventional buried structure type laser diode of this type. To manufacture this laser diode, first, an n-type semiconductor substrate 1
An n-type buffer layer 2, an active layer 3, and a p-type cladding layer 4 are sequentially grown on top of this to form a duffel heteroepitaxial wafer (hereinafter referred to as a DH wafer).

Both sides of the light emitting region of this DH wafer are etched to process the light emitting region into a mesa shape.
Subsequently, the p-type current block layer 10, the n-type current block layer 7, the p-type buried layer 8 and the cap layer 9 are formed.

In the buried structure type semiconductor laser diode having the above structure, in addition to the light emitting region, the n type buffer layer 2, the p type current block layer 10, the n type current block layer 7, and the p type buried layer. 8 forms a thyristor structure, and under an operating condition in which the thyristor is not turned on, the current flows intensively only in the light emitting region.

However, when operating in a high temperature atmosphere or during high power operation, the carriers injected into the p-type current block layer 10 corresponding to the gate region of the thyristor through the cladding layer 4 increase, and the thyristor turns on. Resulting in. The turn-on voltage of this thyristor must be increased in order to operate stably even at high temperature operation and high output operation. For that purpose, carriers can be stored in the p-type current block layer 10 corresponding to the gate of the thyristor as much as possible. It is important to have a structure that does not accumulate.

In the conventional example shown in FIG. 2, the cladding layer 4
Carriers injected into the current blocking layer 10 via
The turn-on voltage of the thyristor is increased by flowing out to the buffer layer 2 through the active layer 3 formed on both sides of the light emitting region.

[0007]

In the conventional buried structure type laser diode described above, the carriers injected into the current blocking layer 10 through the cladding layer 4 flow out to the substrate through the active layer 3 other than the light emitting region. Because there is something to do
In order to increase the turn-on voltage of the thyristor, it is necessary to allow carriers to flow into the active layer with a low resistance. Therefore, in the conventional example, the impurity concentration of the current block layer 10 was increased. However, when the impurity concentration of the current blocking layer 10 is increased, the current flowing from the cladding layer 4 into the current blocking layer 10 increases, which causes problems such as an increase in leak current and an increase in oscillation threshold current.

[0008]

In the semiconductor laser diode of the present invention, the first current of the second conductivity type is formed on both sides of the active layer and the cladding layer of the mesa structure formed on the first conductivity type semiconductor substrate. The semiconductor device is surrounded by a block layer and a second current blocking layer of the first conductivity type, and the clad layer and the second current blocking layer are covered with a second conductivity type semiconductor layer, The first current blocking layer is characterized in that a portion near the semiconductor substrate has a lower carrier concentration than a portion near the second current blocking layer.

[0009]

With the above structure, that is, by sufficiently lowering the carrier concentration in the portion of the first current block layer near the semiconductor substrate, the resistance to the current flowing into the current block layer through the cladding layer is increased. Therefore, the current flowing into the current blocking layer can be reduced. Therefore, this makes it possible to keep the oscillation threshold current low.

The current that once flows into the first current blocking layer flows out to the substrate side through the active layer outside the light emitting region, but in the first current blocking layer, the low carrier concentration layer is the high carrier concentration layer. Since it has a structure backed by, the layer resistance is low as a whole, so that the resistance value to the outflow current can be suppressed low. Therefore, it is possible to increase the turn-on voltage of the thyristor having the current blocking function, and it is possible to operate the thyristor stably under high temperature and high output conditions.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the present invention. In order to manufacture the laser diode of this embodiment, first, on the (100) plane of the semiconductor substrate 1 made of n-type InP, the buffer layer 2 made of n-type InP and InGaAs.
Active layer 3 made of P and having a thickness of 0.08 μm, and p-type I
The clad layer 4 made of nP is sequentially epitaxially grown to form a DH wafer.

On this DH wafer, a groove having a width of 7 μm and a depth of 2 μm is formed on both sides of the light emitting region to form a mesa stripe having a width of 1.5 μm. Then, carrier concentration 1 × 1
0 ¹⁶ cm ^-3 p-type InP low carrier concentration current blocking layer 5 and carrier concentration 1 × 10 ¹⁸ cm ^-3 p-type In
A high carrier concentration current blocking layer 6 made of P is grown, and a current blocking layer 7 made of n-type InP is further grown. Next, p-type InP and p-type InGaAs
P is grown to form a buried layer 8 and a cap layer 9.

In the semiconductor laser diode configured as described above, the current blocking layer in contact with the cladding layer 4 is
Since it is the low carrier concentration current blocking layer 5, the resistance value with respect to the current flowing from the clad layer to the current blocking layer is high, and the concentration of the current in the light emitting region is increased. As a result, the threshold current of laser oscillation is increased. It can be reduced. In fact, in the conventional example of FIG. 2, the threshold current value was 20 mA when the carrier concentration of the current blocking layer 10 was 1 × 10 ¹⁸ cm ^−3.
It was possible to reduce to

Further, the carriers injected from the clad layer 4 into the low carrier concentration current blocking layer 5 can be diffused with a low resistance due to the presence of the high carrier concentration current blocking layer 6, so that the carriers are outside the light emitting region. It quickly flows out to the substrate side through the clad layer 4 and the active layer 3 which are widely spread.
Therefore, the amount of carriers accumulated in the p-type current block layers 5 and 6 corresponding to the gate region of the thyristor structure can be suppressed to a low level, and the turn-on voltage of this thyristor can be increased. According to the above embodiment, 90
It was possible to obtain a light output of 15 mW or more in a high temperature atmosphere of 0 ° C., and to obtain a light output of 200 mW or more in an atmosphere of 25 ° C.

[0015]

As described above, the semiconductor laser diode of the present invention, which has the current blocking layer of the opposite conductivity type to the substrate and the current block of the same conductivity type as the substrate, has the conductivity type opposite to the substrate. Since the carrier concentration of the portion of the current blocking layer close to the substrate is made lower than that of the portion on the opposite side thereof, according to the present invention, the current flowing from the clad layer to the current blocking layer can be suppressed low, The oscillation threshold current value can be reduced.
The carriers flowing into the current block layer of the opposite conductivity type spread rapidly through the high carrier concentration layer and flow out to the substrate side through the clad layer and the active layer with low resistance. The turn-on voltage of the thyristor can be maintained high. Therefore, according to the present invention, it is possible to provide a buried structure type laser diode which has a low threshold current and can stably operate in a high temperature and high output state.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a conventional buried structure type semiconductor laser diode.

[Explanation of symbols]

 1 semiconductor substrate 2 buffer layer 3 active layer 4 clad layer 5 p-type low carrier concentration current blocking layer 6 p-type high carrier concentration current blocking layer 7 n-type current blocking layer 8 buried layer 9 cap layer 10 p-type current Block layer

Claims (1)

[Claims] 1. A semiconductor substrate formed on a first conductivity type semiconductor substrate,
Both sides of the active layer and the cladding layer forming the mesa structure are second
A conductivity type first current blocking layer and a first conductivity type second
A semiconductor laser diode surrounded by a second conductivity type semiconductor layer on the cladding layer and the second current blocking layer, the first current blocking layer being a semiconductor laser diode. A semiconductor laser diode, wherein a portion near the substrate has a lower carrier concentration than a portion near the second current blocking layer.