JP3141430B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser
The present invention relates to a semiconductor laser capable of emitting short-wavelength light, for example, blue, purple, or even ultraviolet light using an nP substrate.

[0002]

2. Description of the Related Art For example, due to the demand for higher density and higher resolution of recording / reproduction for optical disks and magneto-optical disks, blue,
Further, there is an increasing demand for a semiconductor laser that emits light having a short wavelength in the ultraviolet range.

Further, the realization of a blue-emitting semiconductor laser has made it possible to realize various display devices using a semiconductor laser, and further, a color display device using a three-primary-color semiconductor laser.

[0004] In order to construct a semiconductor laser emitting blue or ultraviolet light, a material having a large band gap Eg of a direct transition type is required. Particularly, in a double heterojunction type semiconductor laser, a clad layer having a band gap higher than that of an active layer is required.

Conventionally, II-VI compound semiconductors, particularly IIb-VI compound semiconductors (including mixed crystals of IIb-VI group compounds), are promising as optical device materials having a direct transition type band structure. Have been watched.

On the other hand, IIa-VI group compound semiconductors
Because of the indirect transition type and the stability of the characteristics, they have been reluctant to be used as semiconductor materials for optical devices, especially semiconductor lasers.

On the other hand, in a semiconductor laser, a substrate on which an active layer and a clad layer sandwiching the active layer are epitaxially grown, that is, a commercially available substrate having excellent crystallinity and excellent productivity is used as a substrate. It is desirable.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide, in particular, a substrate constituting a semiconductor laser, that is, an InP substrate which satisfies the above-mentioned conditions required for the substrate, and which emits light of a short wavelength. The present invention provides a semiconductor laser that can be used.

[0009]

That is, in the present invention, in particular, although Mg of group IIa has a large tetrahedral co-crystal radius despite its small atomic number, the IIa-VI by Mg Group semiconductors have a relatively large lattice constant, that is, they are considered to be advantageous for obtaining lattice matching with respect to an InP substrate having a relatively large lattice constant a. Focusing on having a relatively large band gap Eg, containing Mg
II-VI specified by a mixed crystal of a-VI group and IIb-VI group
A group of compound semiconductors has led to the discovery of a semiconductor laser that is well lattice-matched to an InP substrate, has excellent stability such as crystallinity, and therefore has stable emission characteristics, and can emit short wavelength light.

That is, in the present invention, at least cladding layers 2 and 3 and an active layer 4 are epitaxially grown on an InP substrate 1, as shown in FIG. In particular, the cladding layers 2 and 3 are made of a group II-VI containing Mg.

In this basic structure, the cladding layers 2 and 3 are made of, in particular, Mg _x Zn _y Cd _{1 -xy} Se.
(Where x and y are atomic ratios) of a II-VI group compound semiconductor layer composed of a mixed crystal of IIa-VI group and IIb-VI group. In this composition, each of x and y is 0 <x ≦ 0. 95, 0.50 ≧ y ≧ 0.05.

Alternatively, in the basic structure described above, the cladding layers 2 and 3 are formed of Mg _x Cd _{1 -x} S _j Se.
_1-j (where x and j are atomic ratios) a II-VI compound semiconductor layer formed by a mixed crystal of IIa-VI and IIb-VI, and in this composition, x and j are represented by 0 <x ≦ 1, 0.88 ≧ j ≧ 0.03.

[0013] In addition or the above-described basic configuration, the clad layer 2 and 3 constituted by _{MgS k Se 1-k, II} -VI of the active layer _{4 Mg l Zn 1-l Se} (k, L atomic ratio)
Composed of a group III compound semiconductor, and in this composition,
Let k and L be 0.03 ≦ k ≦ 0.13 0.85 ≦ L ≦ 0.95.

[0014]

According to the constitutions of the present invention described above, each clad layer 2
And 3 could be configured as a semiconductor layer having a sufficiently high energy band gap Eg, and could be well matched to the lattice constant (5.8694 °) of the InP substrate. Therefore, according to each of the above-described present inventions, the cladding layers 2 and 3
Of the active layer 4, the band gap of the active layer 4 is smaller than that of the cladding layers 2 and 3, and the difference between the band gaps is smaller than that of the cladding layers 2 and 3. Can be formed by a sufficiently high semiconductor layer while maintaining 0.2 eV or 0.3 eV or more, which can perform various types of short-wavelength light emitting lasers of an optical excitation type, an electron beam excitation type, and an injection type. Can be configured. In addition, II
Due to the constitution of the mixed crystal of the a-VI group and IIb-VI group, the alignment with the InP substrate 1 is favorably performed.
It has been confirmed that a semiconductor laser exhibiting stable and excellent emission characteristics can be obtained despite the addition of g.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to, for example, as shown in FIG.
MBE (molecular beam epitaxy) method, MOCV
The first cladding layer 2, the active layer 4, and the second cladding layer 3 are successively and successively epitaxied by a D (metal organic chemical vapor deposition) method or the like, so that a photo-excited, electron-beam-excited, or injection-type double heterostructure is formed. A junction type semiconductor laser is formed.

For example, a first cladding layer 2 having a thickness of, for example, about 1.0 μm and an
The active layer 4 having a thickness of about 0.2 μm and the second cladding layer 3 having a thickness of about 0.5 μm are sequentially epitaxied. Each of the cladding layers 2 and 3 and the active layer 4 are n-type layers doped with Cl, Ga or the like, and the length of the resonator constituted by the active layer 4 is set to, for example, 100 to 200 μm. In this configuration, an electron beam e is irradiated from the second clad layer 3 side to a stripe-shaped region A extending in a direction perpendicular to the plane of FIG. Resonator end face,
That is, the light emitting end face is constituted by, for example, a cleavage plane of a crystal.

According to such a configuration, 10 A / cm ²
An electron-beam-pumped semiconductor laser that emits light by a certain degree of electron-beam pumping can be constructed.

In order to construct an optically pumped semiconductor laser, the same configuration as that of the above-mentioned electron beam pumped type laser is used.
Excitation is performed by laser light irradiation with a power of about 500 kW / cm ² instead of electron beam irradiation.

Further, in the case of constructing an injection type laser using a pn junction, for example, an n-type InP substrate 1 having a thickness of about 1.0 μm and doped with Cl, Ga, etc. The first cladding layer 2 and a thickness of 0.1 to 0.
An active layer 4 of about 2 μm and O, N
For example, a p-type second cladding layer 3 doped with, for example, is epitaxially grown, and, for example, one electrode (not shown) of In or the like is ohmic-adhered to the entire back surface of the base 1, On the side of the cladding layer 3, another electrode (not shown) made of, for example, Au is applied in a stripe shape in the region A, for example, in an ohmic manner.

Also in this case, the resonator length is 100 to
The thickness can be selected to be about 200 μm, and both ends, that is, light emitting end faces can be formed by cleavage planes of the crystal.

In this case, if a current is applied by applying a required voltage between both electrodes, that is, a voltage of about the band gap of the cladding layer, laser oscillation is performed by recombination of carriers.

Embodiment 1 In each of the above types of semiconductor lasers, the first and second cladding layers 2 and 3 and the active layer 4 have the following composition, and in this quaternary system, Select 2

[0023]

Embedded image Mg _x Zn _y Cd _1-xy Se

## EQU1 ## 0 <x ≦ 0.95

[Equation 2] 0.50 ≧ y ≧ 0.05

In this composition, each of the layers 2 to 4 is made of InP
It matches well with the substrate 1.

In this composition, the band gap Eg of the active layer 4 is smaller than the Eg of the cladding layers 2 and 3, and the difference ΔEg between the two is at least 0.2 eV or more, preferably 0.3 eV or more. . Therefore, the active layer 4
The Eg is 2.3 eV to 3.2 eV (wavelength of about 5 eV).
390 ° to 3874 °), the Eg of the cladding layers 2 and 3 is set to 2.6 eV to 3.5 eV, which is always 0.3 eV or more higher than the Eg of the active layer 4. The active layer 4 is represented by the above formula 1.
In order to satisfy 2.3 eV ≦ Eg ≦ 3.2 eV in the composition of formula (1), the following formulas (3) and (4) are used in the chemical formula (1). At this time, the cladding layers 2 and 3 have the following formulas 5 and 6 in the composition of the chemical formula 1.

## EQU3 ## 0 <x ≦ 0.69

## EQU4 ## 0.50 ≧ y ≧ 0.18

## EQU5 ## 0.23 ≦ x ≦ 0.95

[Formula 6] 0.37 ≦ y ≦ 0.05

Example 2 In Example 1, CdS _q Se _1-q or Zn _p Cd _1-p Se (q and p are atomic ratios) as the active layer 4.
0.78 ≦ q ≦ 0.88, 0.42 ≦ p ≦ 0.52)
(Eg ≒ 2.3 eV). For the cladding layers 2 and 3, the composition of the above formula 1 is used. In this case, x ≧ 0.28 and y ≦ 0.37 are set so that the cladding layers 2 and 3 satisfy Eg ≧ 2.6 eV. In this case, the cladding layers 2 and 3 have an E value of the active layer 4 when the value of x is greater than 0.23 and the value of y is less than 0.37.
g can be increased and confinement can be increased. However, when x becomes too large, that is, Mg
When the amount of addition of Si is large, it is activated to easily take in impurities, or deterioration, variation, and instability of light emission characteristics as a laser due to deterioration of crystallinity due to the occurrence of three-dimensional growth are caused. From the consistency with the above, the active layer 4 has a thickness of 0.95 ≧ x ≧ 0.23, 0.05 ≦ y ≦ 0.3
7 is assumed.

Embodiment 3 In various lasers such as a photo-excitation type, an electron-beam excitation type and a pn junction type laser, the first and second cladding layers 2 and 3 and the active layer 4 have the following composition, In this case, the values of x and j are selected in the following equations (7) and (8).

Embedded image Mg _x Cd _1-x S _j Se _1-j

## EQU7 ## 0 <x ≦ 1

0.88 ≧ j ≧ 0.03 Each layer 2-4 of this composition
Is well matched to the InP substrate 1.

In this composition, the band gap Eg of the active layer 4 is smaller than the Eg of the cladding layers 2 and 3, and the difference ΔEg between them is at least 0.2 eV or more, preferably 0.3 eV or more. In the above Chemical Formula 2, Eg can be selected from 2.4 eV to 3.7 eV in the range of Expression 7, so that when Eg = 2.4 eV in the active layer 4,
The cladding layers 2 and 3 have Eg ≧ 2.7 eV. Therefore, the cladding layers 2 and 3 have x ≧ 0.20 and j ≦ 0.70.
And

[0029] Example 4-excited, electron beam excitation, the p-n junction laser or the like, the first and second cladding layers 2 and 3 MgS _k Se
_1-k (0.03 ≦ k ≦ 0.13) eg MgS _0.08 S
e _0.92 (Eg = 3.8 eV), and the active layer 4 is made of Mg _l Zn _1-l Se (0.85 ≦ L ≦ 0.95) such as Mg _0.91 Zn _0.09 Se (Eg = 3.8 eV). Constitute.

In each of the above-described semiconductor lasers of the present invention, the active layer 4 is confined by the cladding layers 2 and 3 having a large band gap, while being matched with the InP substrate 1 having a large lattice constant by adding Mg. The bandgap of No. 4 could be made large, which enabled emission of short wavelengths from green to purple to ultraviolet.

In the present invention, Mg is added. However, when the cladding layer containing Mg faces the surface of the semiconductor laser, the surface is oxidized by being left in a humid and high temperature for a long time. Figure 2
As shown in (1), the cap layer 5 which does not contain Mg and is not easily oxidized on the upper (second) clad layer 3 can be epitaxially grown following the epitaxial growth of the clad layer 3.

In this case, the cap layer 5 is made of ZnS, ZnSe, or the like, which is easily converted to an n-type and hardly oxidized when the clad layer 3 thereunder is an n-type layer. In the case of a p-type layer, the layer is made of, for example, ZnTe which is easily converted to a p-type and is hardly oxidized.

In FIG. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

In each of the examples according to the present invention described above,
The clad layers 2 and 3 and the active layer 4 are well lattice-matched to the InP substrate 1 and can be grown as a layer having excellent crystallinity. This is because each of the binary compositions shown in FIG. From the relationship between the lattice constant a and the band gap Eg, it can be seen that matching with the InP substrate 1 is possible. In the figure, straight lines d ₁ , d ₂ , and d ₃ are InP, GaAs, and Ga, respectively.
It shows the lattice constant position of P.

In the case of MgZnCdSe, MgSe, Z
In the case of each of nSe and CdSe, at 77 ° K, MgSe is a = 5.89 °, Eg = 3.6 eV, ZnS
e is a = 5.67 °, Eg = 2.79 eV, CdSe is a = 6.05 °, and Eg = 1.82 eV.

[0036]

According to the present invention, a semiconductor laser which is excellent in crystallinity, is relatively inexpensive, and can emit light with a short wavelength using a commercially available InP substrate can be formed.
Magneto-optical recording, furthermore, using these as a light source for optical reproduction, reproduction by the magneto-optical effect, etc., enables high-density recording, high resolution, low power consumption by a semiconductor laser,
It enables high-luminance color display, color image reproduction, and the like, and can bring great benefits in practical use.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a semiconductor laser according to the present invention.

FIG. 2 is a configuration diagram of an example of a semiconductor laser according to the present invention.

FIG. 3 is a measurement diagram of a relationship between a lattice constant a and an energy gap Eg.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 InP base 2 Cladding layer 3 Active layer 4 Cladding layer 5 Cap layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01S 5/327 H01S 5/347

Claims (3)

(57) [Claims] At least a clad layer and an active layer are formed on an InP substrate by epitaxial growth, and at least the clad layer is formed of Mg _x Zn _y Cd _{1 -x -y} S
x, y comprising an e-system II-VI compound semiconductor
(Each atomic ratio) 0 <x ≦ 0.95, 0.50 ≧ y ≧ 0.05. 2. An InP substrate comprising at least a cladding layer and an active layer epitaxially grown on at least the InP substrate, wherein at least the cladding layer is formed of Mg _x Cd _{1 -x} S _j Se.
A semiconductor laser comprising a _1-j group II-VI compound semiconductor, wherein x and j (each an atomic ratio) are selected as 0 <x ≦ 1, 0.88 ≧ j ≧ 0.03. 3. An InP substrate having at least a clad layer and an active layer epitaxially grown on at least the InP substrate. S _K Se _1-K system II
The active layer is made of Mg _L Zn
_1. A semiconductor laser comprising _1-L Se, wherein k and L (atomic ratios) are selected to satisfy 0.03 ≦ k ≦ 0.13, 0.85 ≦ L ≦ 0.95.