JP3469745B2 - Semiconductor laser device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor laser device, and more particularly, to a quantum well cascade type semiconductor laser device which oscillates using a quantum well transition between quantum levels. 2. Description of the Related Art In a conventional semiconductor laser device, carriers are injected using a pn junction to form a population inversion, and injected electrons and holes are recombined by a transition between a conduction band and a valence band. Laser oscillation is realized using this phenomenon. Such a pn junction type semiconductor laser device has problems such as a large current threshold value for laser oscillation, a reactive current, a large power consumption, and difficulty in integration. There are also problems such as oscillation delay and temperature characteristics during modulation. On the other hand, in a material using InGaAs / InAlAs, laser oscillation using transition between quantum levels (hereinafter, referred to as subbands) of a quantum well is faced (J. Faist et al. Science Vo).
l. 264, pp. 553, 1994). A quantum well cascade laser using this intersubband transition can greatly reduce the current threshold for laser oscillation, and can theoretically be a zero threshold laser. However, the laser apparatus of Faith et al. Has a problem that the conduction band offset ΔEc is smaller than 0.6 eV, the oscillation wavelength is 4.2 μm or more, and it is impossible to shorten the oscillation wavelength. Was. Therefore, a quantum well cascade laser device that oscillates in a communication wavelength band has been proposed in Japanese Patent Application Laid-Open No. 8-88440. The laser device disclosed in this publication,
Using InGaAs / AlAsSb as the quantum well,
Laser oscillation is performed at 1.55 μm. This In
Conduction band offset ΔE of GaAs / AlAsSb
c is 1.5 eV. The gain of the quantum well cascade type semiconductor laser device using the quantum well system described above is larger than that of a conventional semiconductor laser device having a transition between a conduction band and a valence electron, but it is still insufficient. Absent. Further, the conduction band offset was not sufficient to further shorten the wavelength. [0007] In view of the above-mentioned conventional problems, the present inventors diligently studied materials used for quantum wells, and in a quantum well cascade type semiconductor laser device, a material having a small lattice mismatch and a high conduction band offset was used. It is another object of the present invention to provide a semiconductor laser device capable of further reducing the current threshold position of laser oscillation and enabling laser oscillation on the short wavelength side. The present invention is directed to a semiconductor laser device that oscillates using transitions between quantum levels in a quantum well. In the above quantum well structure, the conduction band offset and the effective mass of the quantum well are increased, and the quantum well alone can eliminate distortion. As a result, the current threshold of laser oscillation can be greatly reduced, and laser oscillation can be performed at a short wavelength. Further, since the threshold current can be greatly reduced, the power consumption can be reduced and the oscillation delay can be reduced. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a layer structure of a semiconductor laser device according to one embodiment of the present invention, in which a quantum well has a ZnCdTe / HgCdTe quantum well structure. As shown in FIG. 1, n-type Zn _0.70 Cd _0.30
On a Te substrate 1, n-type Mg _0.15 Zn doped with In
Cladding layer 2 made of _0.50 Cd _0.35 Te, ZnCdTe
/ HgCdTe structure quantum well layer 3, In-doped n-type Mg _0.15 Zn _0.50 Cd _0.35 Te cladding layer 4, In-doped n-type Zn _0.65 Cd _0.35 Te contact layer 5 formed by MBE method Have been. [0012] Each carrier concentration of the above layer is 1 ×
10 ¹⁸ cm ⁻³ , the cladding layer 2 is 5 × 10 ¹⁷ to 2 × 10
¹⁷ cm ⁻³ , the quantum well layer 3 is 2 × 10 ¹⁷ cm ⁻³ , the cladding layer 4 is 2 × 10 ¹⁷ cm ⁻³ , and the contact layer 5 is 5 × 10 ¹⁷ cm ⁻³ .
10 ¹⁷ cm ^-3 . Next, the specific configuration of this laser device will be further described. This laser device has an n-type Zn _0.70 Cd _0.30
N-type Mg _0.15 Zn _0.50 Cd having a thickness of 1 μm on a Te substrate 1
_A cladding layer 2 made of _0.35 Te is formed by MBE, and a quantum well layer 3 is formed thereon. The quantum well layer 3 has a carrier concentration of 2 × 10
7 cm thick n-type Zn _0.65 doped with In at ¹⁷ cm ^-3
20 nm thick n doped with Cd _0.35 Te30 and In
A well layer made of type Hg _0.1 Zn _0.55 Cd _0.35 Te31, and an undoped Hg _0.65 Cd _0.35 Te3 film having a thickness of 6 nm.
2 and a carrier concentration of 2 × 10 ¹⁷ cm ⁻³
7 nm thick n-type Zn _0.65 Cd _0.35 doped with In
Well layer of Te33 and undoped Hg of 5 nm thickness
_A barrier layer (light-emitting layer) made of _0.65 Cd _0.35 Te34 is formed by laminating 10 layers in one cycle. On this quantum well layer 3, a cladding layer 4 of n-type Mg _0.15 Zn _0.50 Cd _0.35 Te with a thickness of 1 μm and an n-type Z of 7 nm doped with In with a thickness of 0.1 μm.
contact layer 5 made of n _{0. 65} Cd _0.35 Te are sequentially formed. The ZnCdTe / H formed as described above
In the quantum well layer 3 having the gCdTe structure, photons are laser-oscillated from Hg _0.65 Cd _0.35 Te 34 due to the intersubband transition. The conduction band offset ΔEc of the quantum well layer 3 having the ZnCdTe / HgCdTe structure is 1.9 eV.
The peak gain is as high as 1400 / cm, the current threshold of laser oscillation can be reduced as compared with the conventional quantum well cascade laser, and oscillation can be performed at a short wavelength. Each of the above layers is grown and formed on the substrate 1 by MBE, and the growth temperature is 200 degrees. Table 1 shows the growth conditions of each layer described above. [Table 1] The substrate 1 may be any substrate that matches the lattice constants of the quantum well layer and the barrier layer. For example, an n-type Hg0.7Cd0.3Te substrate can be used in addition to the above-mentioned substrates. FIG. 2 is a schematic diagram showing a layer structure of a semiconductor laser device according to another embodiment of the present invention, in which a quantum well structure uses a ZnCdTe / HgCdSe quantum well structure. On an n-type Zn _0.50 Cd _0.50 Te substrate 1a,
N-type doped with In Mg _0.1 Zn _{0 .55} Cd _0.35 consisting of Te cladding layer 2a, ZnCdTe / HgCdSe structure of the quantum well layers 3a, doped with an In n-type Mg _0.1 Z
A cladding layer 4a made of n _0.55 Cd _0.35 Te and a contact layer 5a made of In-doped n-type Zn _0.5 Cd _0.5 Te are laminated by MBE. The carrier concentration of the above layer is 1
× 10 ¹⁸ cm ⁻³ , and the cladding layer 2a is 5 × 10 ¹⁷ to 2 ×
10 ¹⁷ cm ⁻³ , the quantum well layer 3a is 2 × 10 ¹⁷ cm ⁻³ ,
The cladding layer 4a is 2 × 10 ¹⁷ cm ⁻³ ,
a is 5 × 10 ¹⁷ cm ⁻³ . Next, the specific configuration of this laser device will be further described. This laser device has an n-type Zn _0.50 Cd _0.50
N-type Mg _0.1 Zn _0.55 C having a thickness of 1 μm on a Te substrate 1 a
A cladding layer 2a made of d _0.35 Te is formed by MBE, and a quantum well layer 3a is formed thereon. The quantum well layer 3a is a 7 nm-thick n-type Zn _0.6 Cd _0.4 Te30a doped with In having a carrier concentration of 2 × 10 ¹⁷ cm ^−3.
And In-doped n-type Hg _0.1 Zn doped with In
_A well layer made of _0.55 Cd _0.35 Te31a, an undoped barrier layer made of Hg _0.5 Cd _0.5 Se32a having a thickness of 6 nm, and a 7 nm thick n-type Zn _0.6 doped with In having a carrier concentration of 2 × 10 ¹⁷ cm ^-3 A well layer of Cd _0.4 Te33a and an undoped Hg _0.5 Cd _0.5 Se 3 film having a thickness of 5 nm
The barrier layer (light emitting layer) made of 4a is formed by laminating 10 layers in one cycle. On this quantum well layer 3a, a 1 μm-thick n
Cladding layer 4 of type Mg _0.1 Zn _0.55 Cd _0.35 Te
a and 7 nm thick n doped with 0.1 μm thick In
Contact layers 5a of type Hg _0.5 Cd _0.5 Te are sequentially laminated. The ZnCdTe / H formed as described above
In the quantum well layer 3a having the gCdSe structure, photons are laser-oscillated from Hg _0.5 Cd _0.5 Se 34a by inter-subband transition. The conduction band offset ΔEc of the quantum well layer 3a having the ZnCdTe / HgCdSe structure is 2.0 e.
V, and a peak gain as high as 1500 / cm is obtained. The current threshold value of laser oscillation can be reduced as compared with a conventional quantum well cascade laser, and oscillation can be performed at a short wavelength. Each of the above-mentioned layers is grown and formed on the substrate 1a by the MBE method, and the growth temperature is 200 degrees. Table 2 shows the growth conditions of each layer described above. [Table 2] The substrate 1a may be any substrate that matches the lattice constants of the quantum well layer and the barrier layer. In addition to the above-mentioned substrates, for example, an n-type Hg _0.4 Cd _0.6 Te substrate may be used. FIG. 3 shows that the quantum well of the present invention is made of ZnCdT.
Quantum well cascade type semiconductor laser device formed with an e / HgCdSe structure and ZnCdTe / HgCd
A quantum well cascade type semiconductor laser device having a quantum well formed of an AlAsSb / GaSb structure for comparison with a quantum well cascade type semiconductor laser device formed of a Te structure;
A quantum well cascade type semiconductor laser device in which a quantum well is formed with an AlAsSb / InAs structure and an InGaAsP-based transition band transition semiconductor laser are prepared and oscillated under the conditions of 300 K and an electron density of 2 × 10 ¹⁸ cm ^−3. 4 shows the result of examining the relationship between gain and transition energy of a band laser. The peak gain of the ZnCdTe /
HgCdSe structure of 1500 / cm, ZnC of the present invention
While the dTe / HgCdTe structure is 1400 / cm, the AlAsSb / GaSb structure is 1100 / cm,
AlAsSb / InAs structure of 670 / cm, InGa
According to the present invention, where the AsP-based transition laser between conduction bands is 350 / cm, the gain is large and the laser oscillation current threshold can be further reduced. FIG. 4 shows that the quantum well of the present invention is made of ZnCdT.
Quantum well cascade type semiconductor laser device formed with an e / HgCdSe structure and ZnCdTe / HgCd
A quantum well cascade type semiconductor laser device having a quantum well formed of an AlAsSb / GaSb structure for comparison with a quantum well cascade type semiconductor laser device formed of a Te structure;
A quantum well cascade type semiconductor laser device in which a quantum well is formed in an AlAsSb / InAs structure and an InGaAsP-based inter-conduction band transition semiconductor laser device are prepared, and oscillated under the conditions of 300K and an electron density of 1 × 10 ¹¹ cm ⁻³ , and a peak gain The results of examining the relationship between the transition energy and the transition energy are shown. As can be seen from FIG. 4, according to the laser device of the present invention, the transition is at 1.8 eV,
Laser oscillation can be performed even on the short wavelength side. As described above, in the quantum well structure of the present invention, the conduction band offset and the effective mass of the quantum well are increased, and the quantum well alone can eliminate the distortion, and the laser oscillation Can be greatly reduced and laser oscillation can be performed at a short wavelength. Further, since the threshold current can be greatly reduced, the power consumption can be reduced and the oscillation delay can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a layer structure of a semiconductor laser device according to an embodiment of the present invention, wherein a quantum well is formed of ZnCdT.
An e / HgCdTe quantum well structure is used. FIG. 2 is a schematic diagram showing a layer structure of a semiconductor laser device according to another embodiment of the present invention, in which a quantum well is formed of ZnCd.
It uses a Te / HgCdSe quantum well structure. FIG. 3 is a diagram showing a relationship between gain and transition energy of a 1.55 μm band laser. FIG. 4 shows the results of examining the relationship between the peak gain and the transition energy. [Description of Signs] 1 Substrate 2 Cladding layer 3 Quantum well layer 4 with ZnCdTe / HgCdTe structure 4 Cladding layer 5 Contact layer

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-9-102653 (JP, A) JP-A-9-455993 (JP, A) JP-A-6-334263 (JP, A) JP-A 8- 179387 (JP, A) JP-A-8-236854 (JP, A) JP-A-8-88440 (JP, A) Applied Physics, Japan, 1995, Vol. 64, No. 7, pp. 674-677 (58 ) Surveyed field (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00

Claims (1)

(1) A semiconductor laser device that oscillates using transition between quantum levels of a quantum well, wherein the quantum well is formed of ZnCdT.
e / HgCdSe quantum well structure or ZnCdTe / H
A semiconductor laser device comprising a gCdTe quantum well structure.