JPH06244499A - Laser diode - Google Patents

Abstract

PURPOSE:To prevent the deterioration in crystallizabilities by lattice disorder, by forming ZnS-ZnSe short-period superlattices of a specific component ratio as photoconfinement layers and Zn (S, Se) compounds of a specific ratio as photowaveguide layers, on a GaAs substrate. CONSTITUTION:(ZnS)n-(ZnSe)m short-period superlattices (however n and m are natural numbers, n<5, and 0.1<=n/(n+m)<=0.3) are formed on a silicon added GaAs substrate 1 as photoconfinement layers. Besides, ZnSxSe1-x (0.06<=x<=0.09) layers are formed as photowaveguide layers. The short-period superlattices 2 and 6 have lattice disorder against the GaAs substrate, but their crystallizabilities do not deteriorate by making them very thin. Besides, it becomes possible to suppress the deterioration of the crystallizabilities of the photowaveguides 3 and 5 by making them lattice-match to the substrate. Consequently, it becomes possible to make the efficiency of a blue-range semiconductor laser higher.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to II-VI laser diodes. More specifically, II- in the blue range
The present invention relates to a laser diode using a VI compound semiconductor.

[0002]

2. Description of the Related Art A conventional ZnSe laser diode is
For example, Applied Physics Letter Vol. 59, No. 11, p. 1272 (1991) (Applied Physics Letter v
ol. 59, No. 11, p.1272 (1991)), ZnS _0.07 Se _{0. 0} that lattice-matches a GaAs substrate having high crystallinity as an optical confinement (cladding) layer _{.
The 93} mixed crystal is used, and ZnSe having a lattice mismatch of 0.27% is used as the optical waveguide (waveguide) layer.

[0003]

However, when the ZnSSe-based ternary mixed crystal is used as described above, it is impossible to lattice match both the cladding layer and the waveguide layer to the substrate, and the crystallinity due to the lattice mismatch is inevitable. Was deteriorated.

In order to solve the above problems, the present invention provides
It is an object of the present invention to provide a highly efficient laser diode in which deterioration of crystallinity is suppressed.

[0005]

In order to achieve the above object, the laser diode of the present invention comprises:
As a light confinement layer {(ZnS) _n- (ZnSe) _m }
Short-period superlattice (where n and m are natural numbers and n <
5, 0.1 ≦ n / (n + m) ≦ 0.3), and ZnS _X Se _1-X (where X represents a range of 0.06 to 0.09) as an optical waveguide layer. Is.

[0006]

According to the structure of the present invention, (ZnS) _n (Z
The nSe) _m short-period superlattice has a lattice irregularity with respect to the substrate, but since each layer is very thin, it can be coherently formed on the substrate without deteriorating the crystallinity.
Moreover, since this short-period superlattice is uniform in the growth plane, it does not have the local distortion of strain that is observed in a normal mixed crystal, and is more resistant to strain as a crystal. In addition, ZnS _X Se _1-X (X;
By setting 0.06 to 0.09), it is possible to provide an optical waveguide layer in which deterioration of crystallinity is suppressed. Therefore, GaAs
By forming this (ZnS) _n (ZnSe) _m short-period superlattice on a substrate and using ZnS _X Se _1-X (X; 0.06 to _0.09 ) that is lattice-matched to the substrate as a waveguide layer. Thus, it is possible to achieve a high-efficiency laser diode having excellent crystallinity in the entire device.

[0007]

EXAMPLES The present invention will be described in more detail with reference to the following examples. FIG. 1 is a sectional view schematically showing the structure of a laser diode according to an embodiment of the present invention. A molecular beam epitaxial growth method is preferable as a method for forming this structure.

A GaAs single crystal substrate 1 was used as the substrate, and a low resistance n type substrate was used so that the electrodes could be removed. The temperature of the substrate was set between 200 ° C. and 350 ° C. in order to obtain a ZnSe-based compound semiconductor having good crystallinity. By irradiating the substrate 1 with metal selenium and sulfur molecular beams alternately while irradiating the molecular beam of metallic zinc as a crystal matrix material and zinc chloride (ZnCl ₂ ) as a donor source in an ultrahigh vacuum. 1.2 μm thick chlorinated n-type (ZnS) ₂ (ZnS
e) An ₈ short period superlattice cladding layer 2 was formed. The ALE (atomic layer epitaxy) method was used to form the clad layer, and the film thickness was controlled in atomic layer units. Here, a (ZnS) _n (ZnSe) _m short-period superlattice (n =
2, m = 8) was used, but when the cladding layer thickness is 1.2 μm, G is satisfied if 0.1 ≦ n / (n + m) ≦ 0.3.
The clad layer can be formed on the aAs substrate without deterioration of crystallinity. Moreover, ZnS _X Se _1-X (X;
0.06 to 0.09) Sufficient light could be trapped in the waveguide layer. Further, if the barrier layer thickness of the short-period superlattice was n <5, tunnel conduction of carriers was possible without being significantly affected by the barrier layer.

Next, the substrate is irradiated with all the raw materials at the same time.
And 0.3 μm thick ZnS_0.07Se _0.93Wave guide
Layer 3 was formed. ZnS on GaAs substrate_XSe_1-XMixed crystals
In the case of room temperature, lattice matching occurs at X = 0.06 at room temperature,
Then, lattice matching is performed at X = 0.09. Double with 500 ℃
Conventional epitaxial growth to form heterostructures
It is the highest temperature in the law. This composition range (X; 0.0
6 to 0.09), a film with good crystallinity can be obtained. Well
ZnS_0.07Se_0.93The layer thickness was 1.2 μm
Is 1 μm or more, the light leaks from the waveguide layer
Can be sufficiently reduced practically.

Next, the supply of ZnCl ₂ molecular beam is stopped,
By irradiating the n-type ZnS _0.07 Se _0.93 layer 3 with a molecular beam of metallic cadmium, metallic zinc and metallic selenium,
A Zn _0.9 Cd _0.1 Se active layer 4 having a thickness of m is formed. The Cd composition of the active layer is preferably 0.3 or less. If it exceeds 0.3, due to the difference in lattice constant from the ZnSe waveguide layer,
This is because crystal lattice defects occur during growth and the luminous efficiency is not good. Although the thickness of the active layer 4 is set to 10 nm,
The luminous efficiency was high in the range of 5 nm to 50 nm. If the thickness is less than 5 nm, carriers are not sufficiently accumulated, and 5
When it exceeds 0 nm, lattice relaxation occurs. In either case,
Luminous efficiency is reduced due to poor crystallinity.

Next, an activated nitrogen molecular beam is used as an acceptor source.
By using a molecular beam of metallic zinc, metallic selenium, and sulfur as an active layer
Of 0.3 μm thick nitrogen-doped p-type ZnS_0.07
Se _0.93Waveguide layer 5 was formed.

Further, by irradiating the substrate 1 with the molecular beam of metallic zinc and the molecular beam of active nitrogen while irradiating the molecular beam of metallic zinc and active nitrogen so that the cladding layer 2 is formed, 1.2 μm thick nitrogen is added. p-type (ZnS) ₂ (ZnSe)
_{8 The} clad layer 6 was formed.

Then, an Au electrode 7 was formed on the p-type short period superlattice layer 6 and an In electrode 8 was formed on the back surface of the n-type GaAs substrate 1. Finally, cleavage was performed so that the length and width were each about 500 μm, and cleaved surface mirrors were formed on the end faces to form a resonator.

The laser diode obtained by using the short period superlattice for the cladding layer in this way oscillated in the blue at 485 nm by pulse current injection at room temperature. On the other hand, the laser diode obtained by using the ZnS _0.2 Se _0.8 mixed crystal as the cladding layer without using the short period superlattice did not oscillate.

Zn _0.9 Cd _0.1 Se is used as the active layer.
However, by changing the Cd composition in the range of 0 or more and 0.3 or less, a laser diode of blue to green could be manufactured. Quaternary mixed crystal Z with S added
n _1-Y Cd _Y S _X Se _1-X (X; 0.06 to 0.09,
When Y; 0 to 0.3) was used as the active layer, a laser diode having a shorter oscillation wavelength could be manufactured. All of these had practically high luminous efficiency.

Molecular beam epitaxy was used for crystal growth. In addition to this, MOCVD (metalorganic chemical
Similar growth can be performed by changing the source gas even in a vapor deposition method such as a vapor deposition method. Furthermore, by controlling the layer thickness using the atomic layer epitaxial growth method, the film thickness controllability and crystallinity were further improved, and characteristics such as oscillation threshold and external differential quantum efficiency were improved.

Although chlorine was used as a dopant for the n-type layer, aluminum, gallium, indium, fluorine, iodine and bromine are preferable in that a low resistance sample can be obtained.

Nitrogen was used as the dopant for the p-type layer, but phosphorus, arsenic, lithium and sodium are preferable in that a low resistance sample can be obtained. The carrier density of each layer is 2 × 10 ¹⁷ cm ⁻³ for both n-type and p-type, but it is preferably 5 × 10 ¹⁶ cm ⁻³ or more at room temperature in order to obtain sufficient electric conduction.

Although n-type GaAs was used as the substrate, almost the same characteristics were exhibited even when the structure was reversed in electric conductivity, that is, the device was formed by exchanging p-type and n-type. Further, in this embodiment, the formation of the separate confinement type laser diode is shown, but in addition to this, in any laser structure, G
This (ZnS) _n (ZnS) is added to the optical confinement layer on the aAs substrate.
Se) _m short-period superlattice (n, m: natural number, n <5, 0.
A highly efficient laser diode could be obtained by using the 1 ≦ n / (n + m) ≦ 0.3) layer.

[0020]

As described above, according to the laser diode of the present invention, it is possible to realize the high efficiency of the blue semiconductor laser using the II-VI group compound semiconductor. Such a highly efficient blue laser diode is used for high-density optical recording and
It has a great effect in fields such as information and communication, and is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a laser diode according to an embodiment of the present invention.

[Explanation of symbols]

1 Silicon-added n-type GaAs substrate 2 Chlorine-added n-type (ZnS) ₂ (ZnSe) ₈ Short period superlattice layer (1.2 μm) 3 Chlorine-added n-type ZnS _0.07 Se _0.93 layer (0.3 μm) 4 Zn _0.9 Cd _0.1 Se layer (10 nm) 5 Nitrogen-added p-type ZnS _0.07 Se _0.93 layer (0.3 μm) 6 Nitrogen-added p-type (ZnS) ₂ (ZnSe) ₈ Short period superlattice layer (1.2 μm) 7 Au electrode 8 In electrode

Claims (1)

[Claims] 1. A {(ZnS) _n- (ZnSe) _m } short-period superlattice as an optical confinement layer on a GaAs substrate (where n and m are natural numbers and n <5, 0.1 ≦ n / (n
+ M) ≦ 0.3), and ZnS _X Se as an optical waveguide layer
_1-X (where X represents a range of 0.06 or more and 0.09 or less).