JPH06310809A - Blue-green semiconductor laser - Google Patents

Abstract

PURPOSE:To make it possible to manufacture a blue-green semiconductor laser simply and with good reproducibility and to reduce an oscillation voltage for the laser by a method wherein a double heterostructure, consisting of a ZnCdSe active layer, an n-type ZnSSe clad layer, a p-type ZnSe clad layer and a p<+> ZnSe clad layer, is adopted. CONSTITUTION:A Cl-doped n-type ZnSxSe1-x layer 21 is laminated on an n-type GaAs substrate 10. The composition (x) of the S is set on the condition of 0<=x<=0.2 at a substrate temperature region where the ZnSxSe1-x layer having a good crystallizability is obtained. A Zn1-xCdxSe layer is used as an active layer. Provided that the composition (x) of the Cd is set in the extent of 0.05<=x<=0.5 for obtaining a sufficient difference between the band gaps of the Zn1-xCdxSe active layer 22 and the ZnSSe clad layer 21 in the heterojunction part between the layers 22 and 21. Moreover, a condition that an optical confinement and a carrier confinement in a fundamental mode can be simultaneously satisfied is a condition that the thickness of the active layer is in the extent of 3 to 100nm. Thereby, carriers can be confined and a laser oscillation can take place according to the distortion of the active layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a blue-green semiconductor laser device which uses a II-VI group compound semiconductor and oscillates in a region from blue to green.

[0002]

2. Description of the Related Art The structure of a conventional blue-green semiconductor laser device has a ZnCdSe active layer, a ZnSe separate confinement (SC
It had a structure composed of a H) layer and a ZnSSe clad layer. As a specific example, a single quantum well (SQW-SCH) structure with a separate confinement layer (eg MAHaase et al. Applied
Physics Letters 59, 1272 (1991).) And multiple quantum wells (MQ
W) Structure (eg H. Jeon et al. Applied Physics Letter
s 60 , 2045 (1992).) and multiple quantum well (MQW-SCH) structures with separate confinement layers (eg H. Jeon et al. Applied Phys.
Only ics Letters 59, 3619 (1991).) have been reported.

[0003]

In the prior art, ZnSe is used as the material for the separation confinement layer (SCH). However, since the lattice mismatch exists between the SCH layer of ZnSe and the ZnSSe clad layer, the crystallinity is deteriorated. Therefore, SQW-SCH structure and M
In the QW-SCH structure, the clad layer, the SCH layer, and the active layer have many crystal defects. The presence of crystal defects has a problem that the life of the semiconductor laser device is shortened.

The MQW structure of the prior art is ZnCd.
Se and ZnSe or ZnSSe have a layered structure in multiple layers, but the film thickness is 10n with an accuracy of 1 nm or less.
There is a problem that it is extremely difficult to manufacture a multi-quantum well in which thin films of m or less are stacked in multiple layers with good reproducibility.

Further, in the conventional blue-green semiconductor laser device, in order to improve the contact between the electrode and the p-type layer, for example, Applied Physics Letter Vol. 59, 127.
Page 2 (MA Haase et al. Applied Physics Letters 59 ,
1272 (1991).), Applied Physics Letter, Vol. 60, page 2045 (H. Jeon et al. Applied Physics Le.
tters 60 , 2045 (1992).), Applied Physics Letters Vol. 59, page 3619 (H. Jeon et al. Appli
ed Physics Letters 59, 3619 (1991).) etc., a p ⁺ type Z having a film thickness of about 100 nm as a contact layer.
An nSe layer was provided. However, the voltage during oscillation was 20 V or higher. The lower the voltage during oscillation, the smaller the amount of heat generation, so that the life of the semiconductor laser can be extended. A large oscillation voltage is a big problem in practical use.

Further, when the heat generated in the active layer of the blue-green semiconductor laser is radiated by the junction down die bonding, there is a problem that the heat conduction is poor because ZnSSe is used for the cladding layer of the prior art. It was

The present invention solves the above-mentioned drawbacks and makes it possible to reduce the optical confinement and achieve a single mode without employing an SCH layer which causes crystal defects, and it is possible to easily and reproducibly manufacture. An object is to provide a structure of a blue-green semiconductor laser.

Another object of the present invention is to provide a blue-green semiconductor laser with reduced oscillation voltage and improved heat dissipation.

[0009]

The present invention is 3 nm or more 1
Zn _1-X Cd _X Se having a thickness of 00 nm or less (where X is in the range of 0.05 ≦ X ≦ 0.5) is used as the active layer, and Zn
Se or ZnS _X Se _1-X (where X is 0 <X ≦ 0.2
The conventional problem is solved by a blue-green semiconductor laser in which a p-type clad layer and an n-type clad layer containing any of the above (1) are arranged via one active layer.

[0010]

The blue-green semiconductor laser of the present invention has a thickness of 3 nm or more and 100 nm or less, although the reason is not clear.
Since the active layer of n _1-X Cd _X Se is interposed between the n-type and p-type cladding layers, the strain of the active layer is larger than that of the laser of the conventional double hetero structure laser, and the carrier is generated depending on this strain. It is considered that the laser oscillation was achieved by confining the laser.

[0011]

EXAMPLE A blue-green semiconductor laser of the present invention is a Zn.Cd
-Se active layer is sandwiched between p-type and n-type Zn-Se, p
Type and n-type Zn.S.Se sandwiched, p-type Zn.Se and n-type Zn.S.Se sandwiched, or p-type Zn.S
・ It was demonstrated for the first time that laser oscillation was achieved with a double heterostructure sandwiched between Se and n-type Zn.Se.

Since these structures are extremely simplified structures, they can be manufactured with good reproducibility, instability such as kink is not observed in the optical output, and oscillation is fundamental mode.
It was de.

The composition X of the S component of the p-type and n-type ZnS _X Se _1-X layers can be determined within the range where the lattice matching with the substrate can be obtained depending on the growth temperature.

If the p-type clad layer is made to have a high acceptor density at a distance of 0.1 μm or more from the interface between the active layer and the p-type clad layer to form a p ⁺ -type clad layer, the voltage required for oscillation is about 30%. It was observed to decrease.

The reason for this is not clear, but it is considered that the series resistance of the p-type cladding layer can be reduced as compared with the prior art.

Further, when the heat generated in the active layer of the blue-green semiconductor laser of the present invention is radiated by the junction down, a Zn.Se clad layer is used instead of the Zn.S.Se clad layer of the prior art. Element life is 10
% To 200% was successfully extended.

The reason for this is that since Zn.S.Se of the prior art is a ternary mixed crystal, the thermal resistance is poor and the device life is shortened. However, in the present invention, the binary compound Zn.Se is adopted. Therefore, it can be interpreted that the efficiency of heat dissipation is improved.

(Embodiment 1) FIG. 1 is a structural sectional view of a blue-green semiconductor laser according to an embodiment of the present invention. A molecular beam epitaxy method is used for fabrication.

First, a Cl-doped n-type ZnS _X Se _1-X layer 21 was laminated on the n-type GaAs substrate 10 to a thickness of about 1.5 μm. The composition X of S was determined so as to be lattice-matched with the GaAs substrate 10 at the growth temperature. For example, in the case of this embodiment, the substrate temperature is 325 ° C., so that the range of 0.6 ≦ X ≦ 0.8 is set. However, when the substrate temperature is higher, the S composition X becomes larger. Z with good crystallinity
In the substrate temperature range where nS _X Se _1-X is obtained, the S composition X is 0 ≦ X ≦ 0.2.

The Zn.S.Se layers 21 and 23 were grown by heating and evaporating the metal Zn, the metal Se and the polycrystalline ZnS and irradiating the substrate 10.
For n-type doping, ZnCl ₂ was used as a raw material. carrier concentration of the n-type layer is about 7x10 ^{17 cm-3.}

Zn _1-X Cd _X Se is used as the active layer.
However, the Zn _1-X Cd _X Se active layer 22 and the Zn.S.Se
At the heterojunction of the cladding layers 21 or 23,
In order to obtain a sufficient band gap difference, the Cd composition X needs to be in the range of 0.05 ≦ X ≦ 0.5. Also,
Since the thickness of the active layer depends on the Cd composition, it is difficult to unconditionally define, but the smaller the Cd composition, the thicker the active layer, and the larger the Cd composition, the thinner the active layer pressure. The optical confinement of the basic mode and the confinement of carriers can be satisfied at the same time when the active layer thickness is in the range of 3 nm to 100 nm.

The growth of the Zn.Cd.Se layer 22 is performed by using the metal Z
n and the metal Se and the metal Cd were heated and evaporated, and the substrate 10 was irradiated.

Then, the p-type ZnS _X Se _1-X clad layer 2 is formed.
Grow three. The thickness is about 1.5 μm. ZnS _X S
The composition and growth material of e _1-X are the n-type Zn · S · Se layer 21.
Is the same as. The p-type conversion is achieved by doping nitrogen. Specifically, active nitrogen obtained by converting nitrogen into plasma was irradiated to the growing ZnS _X Se _1-X to obtain a p-type N-doped ZnS _X Se _1-X layer 23. The acceptor density of the p-type cladding layer 23 is 4 × 10.
^{It is 17} cm ^-3 .

Finally, the p ⁺ type ZnSe contact layer 24
To grow MBE. In order to increase the acceptor density, the growth rate was made extremely slow when the contact layer 24 was formed. That is, since the beam intensities of Zn and Se are reduced and the beam intensity of active nitrogen is not changed, more nitrogen enters. Specifically, the growth rate at the time of producing the cladding layer 23 is about 1 μm / h, but the growth rate at the time of producing the contact layer 24 is reduced to about 0.1 μm / h, which is about 1/10. .

The substrate having a double hetero structure obtained by the above method was a stripe type laser which is a rudimentary laser manufacturing process.

A sectional view of the completed laser device is shown in FIG. Insulating layer 41 made of SiO ₂ and having a thickness of about 150 nm
Are laminated by a magnetron sputtering method. Then, the electrode 42 with the p ⁺ type ZnSe 24 is formed by gold vapor deposition.

The laser element has a length of 1 m when cleaved.
m and a width of 0.5 mm. The current is confined by the insulating layer 41 and flows only on the stripes. The width of the stripe is about 10 μm, and the length of the stripe is 1 mm. It was confirmed that laser oscillation occurred when the laser element was cooled to 77K and a pulse current was passed.

However, the oscillation wavelength depends on the Cd composition, and Cd
When the composition is large, the oscillation wavelength becomes long, and the wavelength increases from 460 nm to 5
The area was 70 nm.

FIG. 2 shows the current-light output relationship of a laser device having a Cd composition X = 0.3. The oscillation threshold current density is 40
It was mA. The light output could easily exceed 100 mW per end face. Moreover, it has been confirmed that laser oscillation occurs even at room temperature. The oscillation threshold is 1700m
It was A.

These current-light output characteristics were measured without applying a high reflectance coating or the like to the end face of the laser element. If a high reflectance coating is applied to the end face, a reduction in threshold current can be expected.

Further, the cladding layers 21 and 23 of this embodiment are
It has been confirmed that ZnSe is oscillated even if the material is ZnSe. In this case, a GaAs substrate is used, but Z
If an nSe substrate is used, a clad layer having a lattice matching is obtained, and thus extremely high laser characteristics can be obtained.

Further, in the structure shown in FIG. 1, the substrate 10 and the cladding layers 21 and 23 are lattice-matched. Therefore, the laser structure of the present invention enables coherent growth with few crystal defects. In the electron microscope observation of the laser device of the present invention, the defect density is SQW-SCH structure or MQW-
It has been confirmed that the number is smaller than that of the SCH structure and that it is about the same as the MQW structure.

Since the MQW structure does not have a superlattice structure requiring precision, the laser structure of the present invention is easy to fabricate and has high reproducibility and is extremely practical.

Further, in the laser structure of the present invention, the optical confinement in the active layer region is weaker than that in the MQW structure.
It is thought that the level will increase. Therefore, the laser structure of the present invention shows the possibility of high output.

(Embodiment 2) FIG. 3 is a structural sectional view of a blue-green semiconductor laser according to another embodiment of the present invention. The molecular beam epitaxy method was used for the fabrication.

The growth means is the same as in Example 1, except that p
Type Zn / S / Se clad layer 23 has a thickness of about 0.2 μm.
P ⁺ type Zn.S.
The Se clad layer 25 is formed with a thickness of about 1 μm. Used p
The mold clad layer is optically excellent because it has few non-radiative centers. And its electrical characteristics are that the acceptor density is 4
The resistivity is about 0.7 Ωcm at × 10 ¹⁷ cm ^-3 . The p ⁺ -type cladding layer used has many non-radiative centers and is not optically excellent, but its electrical characteristics are that the acceptor density is 5 × 10 ¹⁷ cm ⁻³ or more and the resistivity is 0.5 Ωcm or less. Is. As described above, when the laser structure of the present invention is used, the number of electrically low resistance p-type regions increases, so that the voltage required for laser oscillation decreases.

FIG. 4 shows the result of current-voltage measurement at 77K. The laser structure shown in FIG. 1 requires a voltage of about 25V. However, when the laser structure of the present invention shown in FIG. 3 is adopted, the oscillation voltage becomes 17V, and there is an effect that the voltage can be lowered by about 30%. Thus, the laser structure of the present invention can significantly reduce the oscillation voltage.

When the acceptor density of the p-type clad layer separated by 0.1 μm or more from the interface between the active layer 22 and the p-type clad layer 23 is 5 × 10 ¹⁷ cm ⁻³ or more of the p ⁺ layer 25, the oscillation voltage is increased. The effect of decreasing Further, the nitrogen concentration of the obtained p ⁺ layer 25 is determined by secondary ion mass spectrometry (SI
It was observed to be 1 × 10 ¹⁸ cm ⁻³ or more by the MS method. That is, it is considered that the nitrogen concentration of 1 × 10 ¹⁸ cm ⁻³ or more is a condition for obtaining the p ⁺ layer.

(Embodiment 3) FIG. 5 shows an embodiment of the present invention.
It is a structure sectional view which mounted a blue-green semiconductor laser. Les
The p-type cladding layer 26 of the laser device is grown to about 0.3 μm.
There is. The acceptor density of the p-type layer 26 is 4 × 10.¹⁷cm
^{ー 3}Is. Following the p-type cladding layer 26, p ⁺Mold cladding
Layer 24 is grown about 1.5 μm. This p⁺Mold layer 24
Has an acceptor density of 8 × 10¹⁷cm^{ー 3}Is. laser
Gold bumps 44 are formed on the element by plating and heat sink
The gold bump 44 side was joined to Ink 45 with In.

The laser element structure of the present invention is characterized in that the cladding layer on the side of the heat sink 45, that is, the material of the p-type cladding layer 26 and the p ⁺ -type contact layer in this embodiment, is a binary compound. The point is that some ZnSe is adopted. The life of the laser device of the present invention is the same as that of the laser structure shown in FIG.
It was confirmed that the life was extended by 10% to 200% as compared with the case of being installed in No. 5.

In the prior art ZnSSe cladding layer, Z
Since it is a ternary mixed crystal of n, S, and Se, the thermal conductivity becomes very poor due to the mixed crystal effect. However, in the present invention, since the binary compound is adopted, it can be interpreted that the efficiency of heat dissipation is improved.

In order to obtain sufficient heat dissipation, it is preferable that the region from the active layer 22 to the heat sink 45 is a binary compound as in the present invention. Alternatively,
Among the clad layers on the side in contact with the heat sink, it is preferable that ZnSe has a thickness of 0.3 μm or more. That is, in the laser structure of FIG.
Even if Se mixed crystal is adopted, the subsequent p ⁺ layer 24 has a thickness of 1 μm.
When ZnSe before and after is used, the heat conduction is p ⁺ type cladding layer 2
It is more effective than the case where all 4 are ZnSSe.

In the present invention, the ZnSe cladding layer 24
And 26, the substrate 10 and the ZnSe clad layer 2
A lattice mismatch exists between 4 and 26 and causes a crystal defect in the ZnSe cladding layers 24 and 26. However, since the active layer 22 is grown before the region where the crystal defect occurs, the influence of the crystal defect is considered to be small.

[0044]

As described above, the present invention is 3 nm or more 1
Zn _1-X Cd _X Se having a thickness of 00 nm or less (where X is in the range of 0.05 ≦ X ≦ 0.5) is used as the active layer, and Zn
Se or ZnS _X Se _1-X (where X is 0 <X ≦ 0.2
Since the blue-green semiconductor laser has a p-type clad layer and an n-type clad layer containing any of the above (1) to be disposed via one active layer, it is possible to cause laser oscillation even at room temperature. .

Since the laser structure is simplified, it can be manufactured with good reproducibility and is excellent in productivity.

Since the p-type clad layer of the blue-green semiconductor laser of the present invention is a p ⁺ -type clad layer having a high acceptor density, the voltage required for oscillation can be significantly reduced.

Further, in the blue-green semiconductor laser clad layer of the present invention, since ZnSe having good thermal conductivity is adopted as the clad layer on the side to be installed on the heat sink, there is an effect that the device life can be extended.

[Brief description of drawings]

FIG. 1 is a structural sectional view of a blue-green semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a light output-current density characteristic diagram of a blue-green semiconductor laser according to an embodiment of the present invention.

FIG. 3 is a structural sectional view of a blue-green semiconductor laser according to an embodiment of the present invention.

FIG. 4 is a current-voltage density characteristic diagram of a blue-green semiconductor laser according to an embodiment of the present invention.

FIG. 5 is a structural cross-sectional view of a blue-green semiconductor laser according to an embodiment of the present invention.

[Explanation of symbols]

10 n-type GaAs substrate 21 n-type ZnSSe clad layer 22 ZnCdSe active layer 23 p-type ZnSSe clad layer 24 p ⁺ type ZnSe contact layer 25 p ⁺ type ZnSSe clad layer 26 p-type ZnSe clad layer 41 insulating layer 42 gold electrode 43 In electrode 44 gold bump 45 heat sink

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigeo Yoshii 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Tsuneo Mikuro, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. Within

Claims (4)

[Claims] 1. A ZnSe or ZnS _X Se layer comprising Zn _{1 -X} Cd _X Se having a thickness of 3 nm or more and 100 nm or less (where X is in the range of 0.05 ≦ X ≦ 0.5) as an active layer.
A blue characterized in that a p-type clad layer and an n-type clad layer containing any of _1-X (where X is in the range of 0 <X ≦ 0.2) are arranged through one active layer. Green semiconductor laser. 2. From the interface between the active layer and the p-type cladding layer,
2. The blue-green semiconductor laser according to claim 1, wherein the p-type cladding layer separated by 1 μm or more has an acceptor density of 5 × 10 ¹⁷ cm ⁻³ or more. 3. The p-type cladding layer is ZnSe or ZnS _x.
Se _1-X (where X is a range of 0 <X ≦ 0.2) containing active nitrogen, and the layer is separated by 0.1 μm or more from the interface between the active layer and the p-type cladding layer. The blue-green semiconductor laser according to claim 2, wherein the nitrogen concentration of the p-type cladding layer is 1 × 10 ¹⁸ cm ^-3 or more. 4. A heat sink is provided on either one of the p-type clad layer and the n-type clad layer, and the clad layer on which the heat sink is provided is ZnSe having a thickness of 0.3 μm or more. A blue-green semiconductor laser according to claim 1.