JPH1187835A - Semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a low threshold and high characteristic temperature, by forming a first optical waveguide layer with first conductivity on a GaAs substrate, and by forming a second optical waveguide layer with conductivity that differs from the first one, so that an active layer region being constituted of a layer including B is pinched on it. SOLUTION: A multiple quantum well structure, where a lower optical waveguide layer 120, a barrier layer 121, and a quantum well layer 122 containing B are alternately laminated, is formed on a first optical waveguide layer 11 with first conductivity being formed on a GaAs substrate. An upper optical waveguide layer is laminated on the multiple quantum well structure, thus forming an active layer region 12 as a whole. Further, an optical waveguide layer 13 with second conductivity that differs from the first conductivity is formed on the active layer region 12, thus obtaining highly efficient laser characteristics with a low threshold current even at a high temperature of approximately 85 deg.C by a semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and a method of manufacturing the same. The present invention relates to a semiconductor laser.

[0002]

2. Description of the Related Art A 13-μm band semiconductor laser for subscriber optical communication is required to have a performance in a high temperature range. One of the causes of the deterioration of the characteristics of semiconductor lasers at high temperatures is that carriers injected into the active layer, especially electrons, become high energy due to heat, exceed the height of the barrier layer, overflow from the active layer, and the luminous efficiency is reduced. Decrease. In a semiconductor laser having a quantum well layer, in order to suppress the overflow of electrons from the quantum well layer, a quantum well structure that increases the energy discontinuity of the conduction band between the quantum well layer and the barrier layer is effective. It is believed that there is. Usually, an InAsP, InGaAs, or InGaAsP layer epitaxially grown on an Inp substrate is used as a material of a quantum well layer that emits light at a wavelength of 1.3 μm or more. Therefore, in order to suppress the overflow of electrons from the quantum well layer, a semiconductor laser structure has been proposed in which a mixed crystal containing Al is used for the barrier layer to increase the conduction band discontinuity. Zah et al., In the IEEE J. Quantum Electoron., Vol. 30, No. 2 (1994), pp. 511-523.
It is reported that good temperature characteristics of about 90 K were obtained in a semiconductor laser using lGaInAs as a barrier layer.

On the other hand, a wavelength of 1.3 μm
Kondo et al. Report a semiconductor laser structure in which the above light emitting layer is epitaxially grown, a quantum well structure is formed by a barrier layer having a large band gap such as AlGaAs or InAlGaP, and the conduction band discontinuity is increased. Kondo et al., "Electronic Letters (Electron
ics, Letters) "Vol. 32, No. 24 (1996) No. 2
On page 244-2245, G on a GaAs substrate
It is reported that a good temperature characteristic of 126 K was obtained at 1.2 μm using a quantum well structure including a quantum well of aInNAs and a GaAs barrier layer as an active layer.

[0004]

However, in the semiconductor laser reported by Zar et al., An AlG
Since the aInAs layer is used, it is difficult to lower the threshold value, and it is difficult to form a conduction band discontinuity larger than that.
On the other hand, in the semiconductor laser reported by Kondo et al., The quantum well light emitting layer is composed of GaInNAs.
In order to emit light at a wavelength of 3 μm or more, it is necessary to further increase the N composition, and it is difficult to form a high-quality GaInNAs epitaxial growth layer. Therefore, 1.3
It is difficult to realize a low threshold semiconductor laser oscillating at μm. An object of the present invention is to provide a semiconductor laser having a low threshold value and a high characteristic temperature.

[0005]

The above object is achieved by the following means.

That is, the present invention provides a first optical waveguide layer having a first conductivity and a second optical waveguide layer having a conductivity different from the first conductivity, which are laminated on a GaAs substrate. And a semiconductor laser having an active layer region sandwiched between the two optical waveguide layers, wherein the active layer region is constituted by at least one layer containing B. Wherein the layer containing B is B
GaAs, BInAs, BGaInAs, BAsSb,
BGaAsSb, BInAsSb and BInGaAsS
b, and the layer containing B is a quantum well layer, a quantum wire layer, or a quantum dot layer.

Further, the present invention provides a first optical waveguide layer having a first conductivity and a second optical waveguide layer having a conductivity different from the first conductivity, which are stacked on a GaAs substrate. And a method for manufacturing a semiconductor laser having an active layer region sandwiched between the two optical waveguide layers, wherein the semiconductor laser is formed by growing at least one layer containing B in the active layer region. Wherein the method of forming at least one layer containing B is gas source molecular beam epitaxy or metal organic chemical vapor deposition, and the layer containing B is BGaAs, BIn.
B is one of As, BAsSb, BGaAsSb, BInAsSb and BInGaAsSb;
Is a quantum well layer, a quantum wire layer or a quantum dot layer.

According to the present invention, a light emitting layer having a wavelength of 1.3 μm or more can be obtained on a GaAs substrate by using a layer containing B. This is because large bowing occurs in the energy gap of the mixed crystal system due to B having a large electronegativity. The material of the barrier layer is GaAs, AlGaAs, InGaP, GaAs, AlGaAs, InGaP, which is a material of a barrier layer or a cladding layer of a normal semiconductor laser having an oscillation wavelength of 0.6 μm to 1 μm on a GaAs substrate.
Since UnAlP, InAlGaP or the like is used, the conduction band discontinuity with the layer containing B can be made large, and
Overflow of electrons to the cladding layer can be reduced.

According to the present invention, BGa is added to the B-containing layer.
As, BInAs, BGaInAs, BAsSb, BG
By using at least one of aAsSb, BInAsSb, and BInGaAsSb, an active layer having a desired oscillation wavelength of 1.3 μm or more can be formed. In particular, the composition of the B-based mixed crystal can be easily controlled, and a high-quality epitaxially grown film can be obtained. Also, by changing the composition, the strain of the epitaxial layer can be controlled.

Further, according to the present invention, it is possible to improve the characteristics of a semiconductor laser device due to a change in state density due to a reduction in dimension by forming the layer containing B into a structure of a quantum well, a quantum wire or a quantum dot. Become.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a sectional structural view of a semiconductor laser according to the present invention. This semiconductor laser is a ridge waveguide type laser. An active layer region 12 is laminated on an n-type optical waveguide layer 11, and a p-type optical waveguide layer 13 is laminated thereon. Furthermore, the high-concentration p-type doped contact layer 14 is
3 are stacked. In order to realize current confinement, the present semiconductor laser has two trench structures 19, and an insulator film 15 is formed in order to prevent a current from flowing except for a ridge portion sandwiched between these two trenches 19. Have been. Finally, a p-type contact metal film 16 and an n-type contact metal film 17 are formed. When a voltage is applied between the two metal films, current flows only in the ridge portion, and light is emitted in the active layer region 12. The generated light is guided in the ridge stripe direction by the upper and lower optical waveguide layers. The end of the stripe is a cleavage plane, and a part of the light is reflected to form an optical resonator as a whole. In this way, laser oscillation can be obtained at a threshold current density or higher.

An important part of the present invention is the configuration of the active layer region 12 described above, which will be specifically described below with reference to a detailed structural diagram. FIG. 1B shows a detailed layer structure of the active layer region 12. Lower optical waveguide layer 120, barrier layer 1
A multiple quantum well structure in which quantum well layers 122 including B and B are alternately stacked, and an upper optical waveguide layer 123 is stacked thereon, and the entire active layer region 12 is formed.
The lower and upper light guide layers 120 and 123 are for improving light confinement in the active layer region. In the present embodiment, the multi-quantum well structure has been described as an example of the active layer. However, the quantum well layer 122 may be a quantum wire layer or a quantum dot layer.

[0014]

Next, a more specific embodiment will be described with reference to FIG.
I will explain. The growth method is gas source molecular beam epitaxy.
Method was used. First, Si dope (3 × 10¹⁸cm^-3)
On a GaAs substrate 20, Si-doped (1 × 10¹⁸cm^-3)
GaAs buffer layer 21, 1.5 μm thick Si doped
(1 × 10¹⁸cm^-3) Al (0.4) Ga (0.6) A
The n-type optical waveguide layer 11 is formed by stacking the s layers 22. continue
40 nm undoped Al (0.2) Ga (0.8) A
s layer 23, 10 nm undoped GaAs layer 24 and 6n
m strain B (0.1) Ga (0.4) In (0.4) As
The quantum well layer 25 is stacked for four periods, and a 40 nm
The doped Al (0.2) Ga (0.8) As layer 26
The active layer region 12 was formed by layering. 1.5μm on it
Thick Be dope (1 × 10¹⁸cm^-3) Al (0.4) G
a (0.6) As layer 27 is laminated to form p-type optical waveguide layer 13
Done. Finally, as a p-type contact layer, a 50 nm thick B
e-doped (5 × 10¹⁸cm^-3) GaAs contact layer 2
8 were laminated. For ridge stripe laser conversion, first
Ridge stripe by lithography and chemical etching
Are formed on both sides of the trench. Ridge strike
In a region other than the top surface of the_Two Insulator film
15 to allow current to be injected only into the ridge stripe
It was to so. Then, Ti / Au p-type contact gold
Metal film 16 and Ti / Au n-type contact metal film 17
And alloyed. Oscillation of this semiconductor laser at room temperature
The wavelength is 1.3 μm and the threshold current density is 1.0 KA /
cm ^Two It is. The characteristic temperature from room temperature to 85 ° C is about
Good characteristics of 120K were obtained.

FIG. 3 shows the band structure of the semiconductor laser of the present invention formed as described above. GaAs barrier layer 2
4 and a strained BGaInAs quantum well layer 25 alternately form a quantum well structure. A characteristic feature of the present invention is that, as shown in FIG.
Emission of a wavelength of 1.3 μm or more is obtained on an As substrate, and a cladding layer of AlGaAs, InGaP, InAlP or the like can be used as a laser structure, so that the electron confinement energy is large and the overflow from the quantum well layer is suppressed. Can be.

Although the present invention has been described with reference to the ridge stripe semiconductor laser, another laser structure such as a buried semiconductor laser may be used. Further, the growth method may be a method other than the gas source molecular beam epitaxy method, for example, a vapor phase growth method such as a metal organic vapor phase epitaxy method. Further, the light confinement structure in the active layer region may be a GRIN-SCH structure in which the composition of AlGaAs is changed. In this embodiment, BGaInA is used as the B-containing layer.
s has been described as an example, but this is BGaAs, BIn
As, BAsSb, BGaAsSb, BInAsSb, and BInGaAsSb may be used.

[0017]

As described above, the semiconductor laser according to the present invention can realize highly efficient laser characteristics with a small threshold current even at a high temperature of about 85 ° C. The reason is B
A high-quality active layer that emits light at a wavelength of 1.3 μm or more can be realized on a GaAs substrate by using a layer containing
This is because, since the cladding layer can be combined with a material system having a large conduction band discontinuity, electron overflow is suppressed, and characteristic deterioration at high temperatures is suppressed.

[Brief description of the drawings]

FIG. 1A is a sectional structural view showing an example of a semiconductor laser of the present invention, and FIG. 1B is an enlarged sectional view of a portion A in FIG. 1A.

FIG. 2 is a sectional structural view of a semiconductor laser according to an embodiment of the present invention.

FIG. 3 is a band structure diagram of the semiconductor laser of the present invention.

[Explanation of symbols]

 Reference Signs List 10 voltage power supply 11 n-type optical waveguide layer 12 active layer region 13 p-type optical waveguide layer 14 high-concentration p-type doped contact layer 15 insulator film 16 p-type contact metal film 17 n-type contact metal film 18 ridge portion 19 trench 120 Lower optical waveguide layer 121 Quantum well layer including barrier layer 122 B 123 Upper optical waveguide layer 20 n-type GaAs substrate 21 n-type GaAs buffer layer 22 n-type Al (0.4) Ga (0.6) As layer 23 Al (0.2) Ga (0.8) As layer 24 GaAs barrier layer 25 BGaInAs quantum well layer 26 Al (0.2) Ga (0.8) As layer 27 p-type Al (0.4) Ga (0. 6) As layer 28 p-type GaAs contact layer

Claims (7)

[Claims] A first optical waveguide layer having a first conductivity, a second optical waveguide layer having a conductivity different from the first conductivity, laminated on a GaAs substrate; A semiconductor laser having an active layer region sandwiched between two optical waveguide layers, wherein the active layer region is formed of at least one layer containing B. 2. The method according to claim 1, wherein the layer containing B is BGaAs, BInA.
The semiconductor laser according to claim 1, wherein the semiconductor laser is one of s, BAsSb, BGaAsSb, BInAsSb, and BInGaAsSb. 3. The semiconductor laser according to claim 1, wherein the layer containing B is a quantum well layer, a quantum wire layer, or a quantum dot layer. 4. A first optical waveguide layer having a first conductivity, laminated on a GaAs substrate, a second optical waveguide layer having a conductivity different from the first conductivity, and A method of manufacturing a semiconductor laser having an active layer region sandwiched between two optical waveguide layers, wherein the method includes growing at least one layer containing B in the active layer region. 5. The method according to claim 4, wherein the method for forming at least one layer containing B is a gas source molecular beam epitaxy method or a metal organic chemical vapor deposition method. 6. The B-containing layer is made of BGaAs, BInA.
6. One of S, BAsSb, BGaAsSb, BInAsSb and BInGaAsSb.
3. The method for manufacturing a semiconductor laser according to item 1. 7. The method of manufacturing a semiconductor laser according to claim 4, wherein the layer containing B is a quantum well layer, a quantum wire layer, or a quantum dot layer.