JPH0878729A - Semiconductor element - Google Patents

Abstract

PURPOSE: To provide a semiconductor element high in reliability, suppressing a deterioration in crystallization due to lattice mismatching. CONSTITUTION: On a crystal surface of an n type GaAs substrate 1, an n type (ZnS)1 (ZnSe)12 strain superlattice layer 2, an n type ZnMgSSe mixed crystal clad layer 3, an n type ZnSSe mixed crystal optical waive-guide layer 4, a ZnCdSe active layer 5, a p type ZnSSe mixed crystal optical waiveguide layer 6, a p type ZnMgSSe mixed crystal clad layer 7, a p type ZnSSe layer 8, a p type Zn(Se, Te) superlattice layer 9 and a p type ZnTe contact layer 10 are successively stacked to form an insulation film 11, a p type electrode 12 and an n type electrode 13. As the (ZnS)1 (ZnSe)12 strain superlattice buffer layer 2 is formed between the clad layer 3 and GaAs substrate 1, crystallization of a higher layer than the strain superlattice buffer layer is enhanced, and also reliability is high without propagating structure defects (dislocation) up to an active layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to prolonging the life of semiconductor devices such as light emitting diodes in the blue to green region, semiconductor laser diodes and the like, which use II-VI group compound semiconductors.

[0002]

2. Description of the Related Art In recent years, in order to increase the density of optical disks and the resolution of laser printers, there is an increasing demand for shorter wavelength semiconductor laser diodes. Conventional blue-green semiconductor laser diodes are, for example, Electronics Letters
9th December 1993 Vol.29 No.25 p.2194 etc.

FIG. 3 is a diagram showing a conventional semiconductor laser diode using a II-VI group semiconductor. In the figure, a ZnSSe mixed crystal buffer layer 42 lattice-matched to the n-type GaAs substrate 41 on the n-type GaAs substrate 41, an n-type Z
nMgSSe cladding layer 43, n-type ZnSSe mixed crystal optical waveguide layer 44, ZnCdSe mixed crystal active layer 45, p-type ZnS
Se mixed crystal optical waveguide layer 46, p-type ZnMgSSe cladding layer 47, p-type ZnSSe layer 48, p-type ZnTe / p-type Z
An nSe multiple quantum well structure 49 and a p-type ZnTe contact layer 50 are sequentially stacked. These are manufactured by the MBE (molecular beam epitaxial growth) method. A Pd / Au electrode as the p-type electrode 52 is in contact with the p-type ZnTe contact layer 50 through the stripe-shaped opening of the insulating film 11 made of TiO ₂ . An In electrode is formed as the n-type electrode 13 on the back surface of the n-type GaAs substrate 41.

[0004]

However, the semiconductor laser diode described above has an extremely short device life of less than 1 second. This is due to structural defects that occur in the early stage of growth. In the initial stage of growth of the n-type ZnSSe mixed crystal buffer layer 42, the GaAs substrate 41 reacts with S (sulfur) to cause Ga
Make S compound. Since this compound has a larger lattice constant than GaAs, if it exists at the interface between the GaAs substrate 41 and the initial growth stage, structural defects (dislocations) due to lattice mismatch occur. S
Also, e (selenium) is not preferable because it forms a compound having a lattice constant different from that of the GaAs substrate 41. In addition, the GaAs substrate 41
Due to the difference in thermal expansion coefficient between the crystal growth layer and the upper layer, structural defects occur during crystal growth or when the temperature is lowered from the crystal growth temperature to room temperature. These structural defects (dislocations) obtain thermal energy from defects such as non-radiative centers and propagate to the active layer 45 to deteriorate the characteristics of the semiconductor device. For this reason, the life is remarkably shortened, which is a serious problem in practical use. In view of the above problems, it is an object of the present invention to provide a highly reliable semiconductor element that suppresses the deterioration of crystallinity due to lattice mismatch.

[0005]

As a means for achieving the above object, the present invention has a buffer layer on a GaAs substrate, a clad layer on the buffer layer, and an active layer above these semiconductor layers. , II-VI group compound semiconductor, a ZnS (zinc sulfide) layer and a ZnSe (zinc selenide) layer are alternately stacked as the buffer layer (ZnS) n (ZnSe).
Provided is a semiconductor device using an m-strained superlattice layer.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing a semiconductor laser diode of a first embodiment of the present invention. In FIG. 1, an n-type GaAs (0015) substrate 1 doped with Si as an n-type impurity by an MBE growth device (not shown).
N-type (ZnS) ₁ (ZnSe) ₁₂ strained superlattice layer 2 doped with Cl as an n-type impurity and n-type Zn _0.9 Mg doped with Cl (chlorine) as an n-type impurity on the crystal plane
_0.1 S _0.18 Se _0.82 mixed crystal cladding layer 3, Cl-doped n-type ZnS _0.07 Se _0.93 mixed crystal optical waveguide layer 4, Zn _0.8 Cd _0.2 Se active layer 5, N (nitrogen) as p-type impurity Doped p-type ZnS _0.07 Se
_0.93 mixed crystal optical waveguide layer 6, p-type Zn _0.9 Mg _0.1 S _0.18 Se _0.82 mixed crystal cladding layer 7 doped with N as a p-type impurity, p-type ZnS doped with N as a p-type impurity
_{A 0.07} Se _0.93 layer 8, a p-type Zn (Se, Te) superlattice layer 9 doped with N as a p-type impurity, and a p-type ZnTe contact layer 10 doped with N as a p-type impurity are sequentially stacked.

As the p-type electrode 52, a Pd / Au electrode is
in contact with the p-type ZnTe contact layer 50 through the stripe-shaped opening of the insulating film 11 made of iO _2. An In electrode is formed as the n-type electrode 13 on the back surface of the n-type GaAs substrate 41.

In the epitaxial growth by the MBE method, the purity is 99.999 as the molecular beam raw material.
9% Zn (zinc), Cd (cadmium), Mg (magnesium), Se (selenium), and S (sulfur) are used, and the n-type doping is performed as an n-type impurity raw material with a purity of 99.999.
9% ZnCl ₂ is used, and p-type doping is performed by irradiating active nitrogen from a nitrogen plasma generated by electron cyclotron resonance as a p-type impurity material.

In order to obtain a semiconductor crystal having good crystallinity, the temperature of the substrate is set between 200 ° C. and 350 ° C., and a Zn molecular beam, which is a ZnSe host crystal material, which has been set to a predetermined vapor pressure in advance in an ultrahigh vacuum. By irradiating the substrate with the molecular beam of ZnCl ₂ which is a doping material simultaneously with the Se molecular beam, Zn
12 monolayers (12 atomic layers) of Se are formed, and then Zn molecule molecules that are ZnS host crystal materials and Zn molecule ₂ that is a donor source doping material and ZnCl ₂ molecules that are the ZnS host crystal material and are preset to a predetermined vapor pressure. By irradiating the substrate with a line, one monolayer (one atomic layer) of ZnS is formed to form one cycle of n-type (ZnS) ₁ (ZnSe) ₁₂ layer and n-type (ZnS) ₁ (ZnSe) ₁₂ A cycle is repeatedly grown until the thickness of the strained superlattice buffer layer 2 reaches 1000 angstrom.

Between the GaAs substrate 1 and the cladding layer 3 of ZnMgSSe mixed crystal lattice-matched to the GaAs substrate 1 (Z
By forming the nS) ₁ (ZnSe) ₁₂ strained superlattice buffer layer 2, structural defects caused by lattice mismatch, thermal expansion coefficient difference, and the like at the substrate interface cause (ZnS) _{1 of the} strained superlattice.
And (ZnSe) ₁₂ have the effect of changing the propagation direction or stopping the propagation at the hetero-interface of the strained layer due to the lattice mismatch, and further repeating (ZnS) ₁ and (ZnSe) ₁₂ in a short cycle. Thus, the propagation of structural defects can be suppressed more effectively. Although (ZnS) ₁ and (ZnSe) ₁₂ have a lattice mismatch, (ZnS)
_{As the 1} (ZnSe) ₁₂ strained superlattice buffer layer 2, G
It is lattice-matched with the aAs substrate and the ZnMgSSe mixed crystal cladding layer 3.

Although the (ZnS) ₁ (ZnSe) ₁₂ strained superlattice buffer layer 2 is used here, the lattice elongation caused by the difference in the thermal expansion coefficient during the growth depending on the growth temperature is taken into consideration.
In order to perform lattice matching with the aAs substrate 1 and the cladding layer 3,
In the (ZnS) n (ZnSe) m strained superlattice buffer layer, the values of n and m are n = 1 to 5 monolayers and m = (10 to 1).
5) It is preferable to change appropriately within the range of xn monolayer.

Further, ZnSe was used as the layer of the (ZnS) ₁ (ZnSe) ₁₂ strained superlattice buffer layer 2 in contact with the GaAs substrate 1, and the compound formed by the reaction between the GaAs substrate 1 and Se is GaAs. Since the lattice constant is closer to that of the GaAs substrate 1 than that of the compound formed by the reaction between the substrate 1 and S, it is possible to suppress structural defects caused by the lattice mismatch between the GaAs substrate 1 and the formed compound, and to form a layer with good crystallinity. This is to form.

Further, the compound of ZnS and ZnSe is used because, when a mixed crystal of these is used, a new lattice defect is generated in the strained superlattice layer due to the composition fluctuation of the mixed crystal, which is favorable. This is because the propagation of structural defects cannot be suppressed.

Next, Zn _0.9 Mg is formed on the strained superlattice layer 2.
_0.1 S _0.18 Se _{0.82 Base} material of Zn molecular beam and S
Molecular beam, Se molecular beam, and Mg preset to a predetermined vapor pressure
ZnC which is a doping material of a donor source at the same time as a molecular beam
n-type Zn _0.9 Mg by irradiating the molecular beam of l _{2
A 0.1} S _0.18 Se _0.82 mixed crystal clad layer 3 is laminated to a thickness of 2 μm. The composition of the Zn _0.9 Mg _0.1 S _0.18 Se _0.82 mixed crystal cladding layer 3 is selected so as to be lattice-matched with the GaAs substrate 2 so as not to generate structural defects due to lattice mismatch with the GaAs substrate 2. If the thickness of the Zn _0.9 Mg _0.1 S _0.18 Se _0.82 mixed crystal cladding layer 3 is 1 μm or more, the leakage of light from the optical waveguide layer 4 can be confined, so that there is no practical problem.

Next, n-type Zn _0.9 Mg _0.1 S _0.18 Se
_By irradiating the _0.82 mixed crystal clad layer 3 with a ZnS _0.07 Se _0.93 matrix crystal material Zn molecular beam, an S molecular beam and a Se molecular beam, simultaneously with a molecular beam of ZnCl ₂ which is a doping material of a donor source, A ZnS _0.07 Se _0.93 optical waveguide layer 4 having a thickness of 2500 Å was formed. Zn
The composition of the optical waveguide layer 4 of S _0.07 Se _0.93 mixed crystal is Zn _0.9
Mg _0.1 S _0.18 Se _{0.82 The} mixed crystal clad layer 3 was selected so as not to generate structural defects due to lattice mismatch.

Next, ZnC as a donor source doping material
The supply of the molecular beam of l ₂ is stopped, and the Zn molecular beam, the Se molecular beam, and the Cd molecular beam previously set to a predetermined vapor pressure are simultaneously n-type Z
nS _0.07 Se _0.93 Mixed crystal optical waveguide layer 4 was irradiated with Zn _0.8 Cd _0.2 Se having a thickness of 60 Å.
The mixed crystal active layer 5 was formed. The thickness of the active layer used here was such that no structural defect is generated during growth due to the difference in lattice constant from the n-type ZnS _0.07 Se _0.93 mixed crystal optical waveguide layer 4.
The Cd composition of the active layer 5 is 0.2 here, but C
By changing the d composition from 0 to 0.3, a semiconductor laser diode from blue to green can be manufactured.

Next, as in the case of forming the n-type ZnS _0.07 Se _0.93 mixed crystal optical waveguide layer 4, active nitrogen, which is a doping material of the acceptor, is supplied instead of ZnCl ₂ to obtain Zn _0.8 Cd _0.2 Se. P-type Zn on the mixed crystal active layer 5
An S _0.07 Se _0.93 mixed crystal optical waveguide layer 6 was formed to a thickness of 2500 Å.

Next, n-type Zn _0.9 Mg _0.1 S _0.18 Se
_{Under the} same growth conditions as the formation of the _0.82 mixed crystal clad layer 3, the Zn molecular beam, the S molecular beam, the Se molecular beam, and the Mg molecular beam are simultaneously doped with active nitrogen, which is a doping material of the acceptor source, into p-type ZnS.
_0.07 Se _0.93 mixed crystal optical waveguide layer 6 is irradiated with p-type Zn _0.9 Mg _0.1 S _0.18 Se _0.82 mixed crystal cladding layer 7
Was laminated to a thickness of 1.5 μm.

Next, under the same growth conditions as the formation of the n-type ZnS _0.07 Se _0.93 mixed crystal optical waveguide layer 4, Zn molecular beam, S molecular beam, and Se molecular beam are simultaneously doped with active nitrogen, which is a doping material of an acceptor source, by p-doping. Type Zn _0.9 Mg _0.1 S _0.18 Se _0.82 p-type ZnS _0.07 by irradiating on the mixed crystal clad layer 7.
A Se _0.93 mixed crystal layer 8 having a thickness of 0.3 μm was formed.

Furthermore, on the p-type ZnS _0.07 Se _0.93 mixed crystal layer 8, p-type ZnS grown simultaneously from Zn molecular beam and Se molecular beam from active nitrogen which is a doping material of an acceptor source.
e layer, Zn molecular beam and T preset to a predetermined vapor pressure
At the same time as the e molecular beam, a p-type ZnTe layer grown from active nitrogen, which is a doping material of the acceptor source, is alternately p-typed.
Type ZnSe is 18 angstrom and p type ZnTe is 2
Angstrom, p-type ZnSe is increased by 17 angstrom, p-type ZnTe is increased by 1 angstrom such as 3 angstrom, and p-type ZnSe is repeatedly laminated until it becomes 2 angstrom and p-type ZnTe becomes 18 angstrom, and p-type Zn (Se, Se, Te) Superlattice layer 9
To form. Then, a p-type ZnTe layer having a thickness of 300 Å is laminated to form a contact layer 1 of the p-type electrode 12.
Set to 0. The p-type Zn (Se, Te) superlattice layer 9 used here gradually relaxes the current barrier in the valence band between the p-type ZnS _0.07 Se _0.93 mixed crystal layer and the p-type ZnTe contact layer 10. It has a smoothing effect as a whole, so that the injection current can be made to flow efficiently.

After the wafer having the above structure is taken out from the MBE growth apparatus, a current confinement layer TiO ₂ 11 having a thickness of 2000 angstrom is laminated by sputtering. After forming a stripe-shaped opening by photolithography, a Pd film having a thickness of 100 Å and an Au film having a thickness of 4000 Å are sequentially stacked by a vapor deposition method, and heat treatment is performed at 250 ° C. for 1 min in a nitrogen atmosphere to form a p-type film. The electrode 12 is formed. In addition, n-type GaA
The n-type electrode 13 on the s substrate 1 side is formed by vapor deposition of In. Finally, cleavage is performed so that each length and width is about 0.3 mm to 1 mm, and a cleavage plane mirror is formed to form a resonator.

The semiconductor laser diode thus obtained oscillates in blue-green at room temperature due to current injection, and is compared with a semiconductor laser diode in which the strained superlattice layer 2 is not included.
The optical output with respect to the injection current increased significantly, and the time until the semiconductor laser diode stopped oscillating significantly increased. Therefore, a highly efficient and highly reliable semiconductor laser diode can be manufactured, which is very effective for high density optical recording and information related equipment.

A second embodiment of the present invention will be described below. FIG. 2 is a sectional view schematically showing the structure of the light emitting diode of the second embodiment of the present invention. In the figure, M
N doped with Si as an n-type impurity by the BE method
N-type (ZnSe) 1 (ZnS) doped with Cl as an n-type impurity on the crystal plane of the n-type GaAs (100) substrate 21.
e) 12-strained superlattice layer 22, n-type ZnMgSSe mixed crystal cladding layer 23 doped with Cl as an n-type impurity, Zn _0.8 Cd _0.2 Se / ZnSe active layer 2 having a multiple quantum well structure
4, p-type Zn _0.9 M doped with N as a p-type impurity
g _0.1 S _0.18 Se _0.82 mixed crystal cladding layer 25, p-type ZnS _0.07 Se _0.93 layer 2 doped with N as a p-type impurity
6, p-type Zn (S doped with N as a p-type impurity)
e, Te) superlattice layer 27 and p-type ZnTe contact layer 28 doped with N as a p-type impurity are sequentially stacked. Then, on the p-type ZnTe contact layer 28, a Pd / Au electrode as a p-type electrode 29 is circularly formed on the p-type ZnT contact layer 28.
e is in contact with the contact layer. On the other hand, an In electrode is formed as the n-type electrode 30 on the back surface of the n-type GaAs substrate.

Epitaxial growth by the MBE method is performed under the same growth conditions using the same molecular beam raw material and doping material as in the first embodiment. First, as in the first embodiment, n-type (ZnSe) ₁ (Z
nSe) ₁₂ strained superlattice layer 22, n-type Zn _0.9 Mg _0.1 S
_0.18 Se _0.82 mixed crystal clad layers are sequentially laminated.

Next, n-type Zn _0.9 Mg _0.1 S _0.18 Se
_{On the 0.82} mixed crystal cladding layer 23, a Zn _0.8 Cd _0.2 Se mixed crystal well layer having a thickness of 60 Å was irradiated by irradiating Zn molecular beam, Se molecular beam and Cd molecular beam, and Zn molecular beam and S.
e Z-ray having a thickness of 100 angstrom by irradiating with molecular beam
Zn _0.8 Cd _0.2 Se / ZnS having a multiple quantum well structure in which an nSe barrier layer is grown and six layers are alternately laminated.
e The active layer 24 is formed.

Furthermore, on the active layer 24 of the Zn _0.8 Cd _0.2 Se / ZnSe multiple quantum well, as in the first embodiment,
p-type Zn _0.9 Mg _0.1 S _0.18 Se _0.82 mixed crystal clad layer 2
5, p-type ZnS _0.07 Se _0.93 layer 26, p-type Zn (Se,
Te) Superlattice layer 27 is sequentially laminated.

After the wafer having the above structure is taken out from the MBE growth apparatus, the Pd film 1 is formed by the lift-off method.
00 angstrom and Au film 4000 angstrom were sequentially laminated, and 250 ° C. and 1 mi in a nitrogen atmosphere.
A heat treatment of n is performed to form a circular p-type electrode 29. Further, In is formed by vapor deposition as an n-type electrode on the n-type GaAs substrate side. Lastly, dicing is performed so that the length and width are each about 0.3 mm to obtain a light emitting diode.

The light emitting diode thus obtained emits a blue-green color at room temperature, and compared with a light emitting diode without the strained superlattice layer 22, the light output with respect to the injection current is significantly increased, and the light emitting diode The time required for the emission intensity to reach 80% of the initial emission intensity was significantly extended. Therefore, light emission with high efficiency and high reliability can be manufactured, which is a great effect for a related device using a light emitting diode.

Although the n-type GaAs substrate is used for explanation here, the same effect can be expected with an element structure having an opposite conductivity type. Although the MBE method is used as the crystal growth method, other similar vapor phase growth methods such as the MOVPE method can be used for the same growth. Further, as the structure of the semiconductor laser diode, the description has been made by using the separate confinement type double hetero structure semiconductor laser diode, but the same effect can be obtained even in the normal double hetero semiconductor laser diode structure.

[0030]

As described in detail above, according to the present invention,
Since the (ZnS) n (ZnSe) m strained superlattice layer is used as the buffer layer between the cladding layer and the GaAs substrate,
Structural defects caused by lattice mismatch or difference in coefficient of thermal expansion at the substrate interface change the propagation direction or stop propagation at the hetero interface of the strained superlattice, increasing the crystallinity of the upper layer from this buffer layer. As a result, structural defects (dislocations) do not propagate to the active layer, and a highly reliable semiconductor device can be obtained.
Therefore, high reliability of the semiconductor laser and the light emitting diode in the blue region using the II-VI group compound semiconductor can be realized, which is extremely effective in practice.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing the structure of a light emitting diode according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing a structure of a conventional semiconductor laser diode.

[Explanation of symbols]

 1 substrate 2 strained superlattice buffer layer 3 clad layer 4 optical waveguide layer 5 active layer 6 optical waveguide layer 7 clad layer 9 superlattice layer 10 contact layer 11 insulating layer 12 p-type electrode 13 n-type electrode

Claims (3)

[Claims] 1. A semiconductor device using a II-VI group compound semiconductor, comprising a buffer layer on a GaAs substrate, a clad layer on the buffer layer, and an active layer above these semiconductor layers. ZnS (zinc sulfide) layer as a buffer layer, and Z
nSe (zinc selenide) layers were alternately laminated (Zn
A semiconductor device using an S) n (ZnSe) m strained superlattice layer. 2. The (ZnS) n (ZnSe) m strained superlattice layer comprises n = 1 to 5 monolayers and m = (10 to 15) ×.
The semiconductor element according to claim 1, wherein the semiconductor element is an n monolayer. 3. The crystal layer of the (ZnS) n (ZnSe) m strained superlattice layer grown first on a GaAs substrate is the Z layer.
The semiconductor device according to claim 1, which is an nSe layer.