JPH0545078B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to semiconductor lasers, and more particularly to dual-channel planar buried structure semiconductor lasers.

[Conventional technology]

The conventional dual-channel planar buried structure semiconductor laser shown in FIG. 2 includes an N-type semiconductor substrate 1 made of InP, an N-type cladding layer 2 made of InP,
After epitaxially growing the active layer 3 made of InGaAsP and the P-type cladding layer 4 made of InP, 1
A pair of grooves 11 are formed, and a P-type block layer 6 made of InP, a non-doped layer 7 made of InP, and an N-type block layer 8 made of InP are formed on the surface except for the striped mesa portion 12 sandwiched between the grooves 11. form,
Thereafter, a P-type semiconductor layer 9 made of InP and a cap layer 10 made of P-type InGaAsP were formed over the entire surface. Therefore, the P-type semiconductor layer 9, the N-type block layer 8, the P-type block layer 6, and the N-type cladding layer 2 constitute a PNPN thyristor, which has the effect of blocking the flow of current. can be effectively injected into the active layer light emitting part (the active layer 3 in the striped mesa part). Furthermore, outside the trench region, the active layer 3 with a small forbidden band width creates a potential barrier between the active layer 3 and the P-type cladding layer 4, and the
The proportion of electrons injected into the type cladding layer 4 is reduced, making it difficult to turn on the thyristor.

[Problem that the invention seeks to solve]

In the conventional device shown in FIG. 2, the active layer 3 with a small forbidden band width is not formed in the groove 11 region.
Injection of electrons from the N-type cladding layer 2 to the P-type blocking layer 6 can be performed relatively easily. Therefore,
In the conventional element, as the applied voltage is increased after laser oscillation, the P-type semiconductor layer 9, the N-type block layer 8, the non-doped layer 7,
The current flowing through the P-type block layer 6 and the N-type cladding layer 2 increases, that is, the current flowing through the P-type semiconductor layer 9 passes through the striped mesa portion 12 of the P-type cladding layer 4, and the current flows through the P-type block layer 6. When the current flowing into 6 acts as the gate current of the PNPN thyristor and increases the applied voltage, 9, 8,
The thyristor composed of 6 and 2 was turned on and the leakage current increased. As a result, a problem occurred in that the differential quantum efficiency of the device deteriorated.

[Means for solving problems]

The double-channel type buried-brainer structure semiconductor laser of the present invention is a multilayer film in which at least three layers, a first conductivity type cladding layer, an active layer, and a second conductivity type cladding layer, are sequentially laminated on a first conductivity type semiconductor substrate. a striped mesa portion in which a pair of mutually parallel grooves having a depth penetrating at least the active layer are formed on the surface of the substrate; a portion of the striped mesa portion excluding the surface thereof is provided in a sequentially laminated manner; a second conductivity type barrier layer and a first conductivity type barrier layer having a larger band gap than the active layer; and a second conductivity type barrier layer made of the same semiconductor as at least one of the cladding layers.
a conductive type block layer and a first conductive type block layer;
a second conductivity type semiconductor layer covering a surface of the striped mesa portion and a surface of the first conductivity type block layer, wherein the second conductivity type block layer is in contact with the second conductivity type cladding layer at the striped mesa portion. A current is selectively injected into the striped mesa portion.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor chip showing the main parts of a dual channel type planar buried structure semiconductor laser related to an embodiment of the present invention.

This double channel type planar buried structure semiconductor laser is laminated on an N-type semiconductor substrate 1 made of InP, an N-type cladding layer 2 made of InP, an active layer 3 made of non-doped in _0.65 Ga _0.35 As _0.79 P _0.21 , and
An active active layer is provided on the surface of the heterojunction structure including at least the N-type cladding layer 4 made of InP, except for the surface of the striped mesa portion 12, which is sandwiched between a pair of grooves 11 deeper than the active layer 3. Barrier layer 5 is made of N-type In _0.76 Ga _0.24 As _0.55 P _0.45 , which has a larger forbidden band width than layer 3, and InP is the same as each cladding layer 2 and 3.
P-type block layer 8 and N-type block layer 8 consisting of
and a P-type semiconductor layer 9 covering the surface of the striped mesa portion 12 and the surface of the N-type block layer 8, and current is selectively injected into the striped mesa portion 12.

Next, a method for manufacturing this double channel type planar buried structure semiconductor laser will be explained.

First, on an N-type semiconductor substrate 1 made of InP, a thickness of
N-type InP layer 2 with a thickness of 3 μm and an impurity concentration of 5×10 ¹⁷ cm ^-3 ;
Non-doped In _0.65 Ga _0.35 As _0.79 P _0.21 layer 3 with a thickness of 0.1 μm, P type with a thickness of 1 μm and an impurity concentration of 1×10 ¹⁸ cm ^-3
After forming the InP layer 4, a pair of grooves 11 with a depth of 4 μm and a width of 8 μm deeper than the position of the active layer 3 are formed,
Furthermore, the active layer 3 is placed on the striped mesa portion 12 with a width of 1.5 μm sandwiched between the pair of grooves 11, and on the active layer 3 of the grooves 11.
1 μm thick on the surface excluding the area above the position.
N-type In _0.76 Ga _0.24 As _0.55 with impurity concentration 1×10 ¹⁸ cm ^-3
After forming P _0.45 layer 5, striped mesa part 1
A P-type InP layer 6 with a thickness of 1 μm and an impurity concentration of 1×10 ¹⁸ cm ^-3 excluding the top layer 2, a non-doped InP layer 7 with a thickness of 0.5 μm,
N-type InP with a thickness of 1.1 μm and an impurity concentration of 1×10 ¹⁸ cm ^-3
Layer 8 is formed, and then P-type InP is formed on the entire surface.
A layer 9 and a P-type InGaAsP layer 10 are formed.

In this double channel type planar buried structure semiconductor laser, since the barrier layer 5 having a larger forbidden band width than the active layer 3 is provided in the trench 11 region, electrons are injected from the N-type cladding layer 2 into the P-type blocking layer 6. The proportion of leakage flowing through 9, 8, 7, 6, 5, 2 is reduced by suppressing the turn-on current of the thyristor in the groove 11 region. The current is reduced to less than 1/3 of the conventional example. or,
The leakage current flowing through 4, 6, 5, and 2 (current flowing into the trench from outside the trench) hardly changes because the forbidden band width of the barrier layer 5 is larger than that of the active layer and there is no absorption of light. As a result of this reduction in leakage current, the external differential quantum efficiency η (%) is lower than that of the conventional example η ₀
(%), an improvement of 5% or more (η≧η ₀ +5).

FIG. 3 is a sectional view of a semiconductor chip showing the main parts of an embodiment of the present invention.

In this example, the depth of the groove 11 is 4.4 μm, the thickness of the barrier layer is 0.7 μm, and the impurity concentration is In _0.76 of 1×10 ¹⁸ cm ^-3 .
N-type barrier layer 5a consisting of Ga _0.24 As _0.55 P _0.45 and its thickness
In _0.76 Ga _0.24 with impurity concentration of 1×10 ¹⁸ cm ^-3
The second embodiment is the same as the first embodiment except that it includes a P-type barrier layer 5b made of As _0.55 P _0.45 . Therefore, the P-type InP layer 6, the N-type InGaAsP layer 5a, the P-type
The InGaAsP layer 5b and the N-type InP layer 2 constitute a PNPN thyristor, and the leakage current flowing from the P-type InP layer 4 through each growth layer constituting the above-mentioned PNPN thyristor is less than 1/5 of that of the conventional element. Ta.
On the other hand, P-type InP layer 9, N-type InP layer 8, non-doped
InP layer 7, P-type InP layer 6, N-type InGaAsP layer 5a,
The leakage current flowing through the P-type InGaAsP layer 5b and the N-type InP layer 2 is reduced to 1/5 of that of the conventional element due to the fact that it flows through the PNPNPN junction and the effect of the potential barrier between the P-type InP layer 6 and the N-type InGaAsP layer 5b. It became the following. As a result, the external differential quantum efficiency of the device of this example is improved by more than 8% compared to the conventional device (η≧η ₀ +
8) was achieved.

〔Effect of the invention〕

As explained above, the present invention provides a potential barrier by a heterojunction with the second conductivity type block layer by inserting a barrier layer into the groove region,
By lowering the injection rate of carriers injected from the first conductivity type block layer into the second conductivity type block layer, leakage current can be reduced and the external differential quantum efficiency of the device can be improved.

[Brief explanation of drawings]

1 and 3 are cross-sectional views of a dual-channel planar buried structure semiconductor laser and a semiconductor chip showing the main parts of one embodiment, respectively, related to an embodiment of the present invention, and FIG. 1 is a cross-sectional view of a semiconductor chip showing the main parts of a planar buried structure semiconductor laser; FIG. DESCRIPTION OF SYMBOLS 1... N-type semiconductor substrate, 2... N-type cladding layer, 3... Active layer, 4... P-type cladding layer, 5,
5a, 5b...barrier layer, 6...P type block layer,
7... Non-doped layer, 8... N-type block layer, 9
...P-type semiconductor layer, 10...cap layer, 11...
...Groove, 12...Striped mesa part.

Claims (1)

[Claims] 1. On the surface of a multilayer film substrate in which at least three layers, a first conductivity type clad layer, an active layer, and a second conductivity type clad layer are sequentially laminated on a first conductivity type semiconductor substrate, a layer with a depth that penetrates at least the active layer is formed. a striped mesa portion formed by a pair of grooves parallel to each other; and a second conductivity type having a wider forbidden band width than the active layer, the striped mesa portion being sequentially laminated on a portion other than the surface of the striped mesa portion. a barrier layer and a first conductivity type barrier layer; a second conductivity type block layer and a first conductivity type block layer made of the same semiconductor as at least one of the cladding layers; a second conductive type semiconductor layer covering a surface of the conductive type block layer, the second conductive type block layer being provided in contact with the second conductive type cladding layer in the striped mesa portion and selected in the striped mesa portion. 1. A dual-channel planar buried structure semiconductor laser, characterized in that a current is injected selectively.