JPH088484A - Electrode for light emitting and receiving element made of II-VI group compound semiconductor - Google Patents

Abstract

PURPOSE:To provide an electrode used for a light emitting/detecting device formed of II-VI compound semiconductor and capable of making ohmic contact with a P-type II-VI compound semiconductor crystal layer. CONSTITUTION:An electrode of a light, emitting/detecting device formed of II-VI compound semiconductor is composed of a P-type diamond carbon layer 21 formed on a P-type II-VI compound semiconductor layer 20 and a metal layer 22 formed on the carbon layer 21. Or, an electrode is composed of a P-type BETA-SiC layer (SiC layer of zinc blende structure that Si and C constitute a face-centered cubic lattice) formed on a P-type II-VI compound semiconductor layer and a metal layer provided onto the SiC layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for a light emitting / receiving element made of a II-VI group compound semiconductor, and more particularly to improvement of a so-called p-type electrode.

[0002]

2. Description of the Related Art ZnSe, ZnSSe, ZnMgSSe
Wide-gap II-VI group compound semiconductors such as the above are regarded as promising materials for short-wavelength (green, blue) light emitting diodes and semiconductor lasers. LED using ZnSe
Has a basic structure of n-type II-V formed on an n-type compound semiconductor substrate made of GaAs or ZnSe, for example.
A group I compound semiconductor crystal layer, a p-type II-VI group compound semiconductor crystal layer, a cap layer made of a p-type II-VI compound semiconductor crystal, and a metal electrode. Also,
The basic structure of a semiconductor laser having a double hetero structure using ZnSe is, for example, an n-type compound semiconductor substrate, an n-type I
First clad layer composed of I-VI group compound semiconductor crystal layer, active layer, second clad layer composed of p-type II-VI compound semiconductor crystal layer, cap layer composed of p-type II-VI compound semiconductor crystal , And a metal electrode. The metal electrode is made of, for example, Pd / Pt / Au. Further, low contact specific resistance and highly reliable ohmic contact are required between the cap layer and the metal electrode. The cap layer has a function as a contact layer and a function as an antioxidant layer of the II-VI group compound semiconductor crystal layer formed thereunder.

[0003]

However, under the present circumstances,
The contact between the cap layer and the metal electrode is a Schottky junction, and there is a problem that a current does not flow unless a high voltage is applied to the metal electrode. This is because the energy level of the valence band of the II-VI group compound semiconductor is deeper than the energy level of electrons responsible for electric conduction in the metal electrode, and the carrier concentration obtained in the p-type II-VI group compound semiconductor. Is as low as about 10 ¹⁸ / cm ³ .

Further, in order to improve the luminous efficiency of a light emitting element composed of a surface emitting diode or a surface emitting semiconductor laser, when the light generated inside the light emitting element is emitted to the outside,
The light should not be blocked by the electrodes. Therefore, when using an opaque electrode such as a metal electrode,
An electrode is formed outside the light emitting region so that the light emitting region is not covered with the electrode. In such a structure, it is necessary that the current flowing through the electrode is sufficiently spread in the compound semiconductor crystal layer in the light emitting region. By the way, p
Since the type II-VI group compound semiconductor has high resistance, it is difficult for current to sufficiently spread in the compound semiconductor crystal layer in the light emitting region. As a result, there is a problem that only the region directly under the electrode emits light, and it is difficult for the entire light emitting region to emit light. Since ITO, ZnO, and the like, which form the conventional transparent electrode, are n-type semiconductor materials, they cannot be ohmic electrodes having low resistance with the p-type II-VI group compound semiconductor crystal layer.

If a II-VI group compound semiconductor crystal layer is grown on a p-type compound semiconductor substrate made of GaAs and the uppermost layer is a cap layer made of an n-type II-VI group compound semiconductor crystal, ITO, ZnO, or the like is used. Conventional transparent electrodes can be used. Further, a metal electrode having ohmic contact and having a low contact specific resistance value can be easily formed on the n-type II-VI group compound semiconductor crystal layer. Therefore, it is possible to avoid the above problems. However, when such a light emitting device structure is formed on a p-type compound semiconductor substrate, it is more likely to have Ga than ZnSe.
As has a shallow valence band energy band of about 1.4 eV, a Schottky junction is formed between the p-type compound semiconductor substrate and the p-type II-VI group compound semiconductor crystal layer, and a high driving voltage is also required. become.

Also in the light receiving element, like the light emitting element,
Since a Schottky junction is formed between the p-type II-VI group compound semiconductor crystal layer and the metal electrode, the p-type II-VI is formed.
There is a problem that it becomes difficult for current to flow between the group compound semiconductor crystal layer and the metal electrode.

Therefore, an object of the present invention is to provide p-type II-VI.
I capable of forming ohmic contact with the compound semiconductor crystal layer, I
An object of the present invention is to provide an electrode for a light emitting element or a light receiving element which is made of a group I-VI compound semiconductor.

[0008]

An electrode for a light emitting and receiving element comprising a II-VI group compound semiconductor of the present invention for achieving the above object is formed on a p-type II-VI group compound semiconductor crystal layer. And a p-type diamond-based carbon layer and a metal layer formed thereon. Here, the diamond-based carbon layer is a layer made of single crystal or polycrystal diamond, or a layer made of amorphous carbon in which carbon such as diamond-like carbon or i-carbon is sp ³ -bonded. Means

Alternatively, an electrode for a light emitting and receiving element made of a II-VI group compound semiconductor of the present invention for achieving the above object is a p-type formed on a p-type II-VI compound semiconductor crystal layer. .Beta.-type SiC layer (SiC layer having a zinc blende type structure in which Si and C form a face-centered cubic lattice), and a metal layer formed thereon. β
The type SiC layer may be crystalline or amorphous.

In these electrodes for light emitting and receiving elements made of II-VI group compound semiconductors of the present invention, p-type II
The -VI group compound semiconductor crystal layer includes p-type ZnSe and p-type Z
It can be composed of nSSe or p-type ZnMgSSe. Au, Ti, P are used as materials for the metal layer.
Mention may be made of t, Pd and their alloys or multilayers. The term light emitting / receiving element in this specification includes a light emitting element and a light receiving element.

The light emitting and receiving element in the present invention includes any light emitting and receiving element in which a portion where an electrode is to be formed is composed of a p-type II-VI group compound semiconductor crystal layer, for example, a double hetero structure. (DH), separate confinement heterostructure (SCH), multiple quantum well structure (MQW), edge emitting type or surface emitting type pn junction type light emitting diode, semiconductor laser, photodiode, multiple quantum well structure (MQW) An optical absorption modulator having Alternatively, the light emitting / receiving element of the present invention may include a semiconductor laser having a one-dimensional quantum well structure or a two-dimensional quantum well structure, and further, GRIN-SC.
H semiconductor laser, lateral current injection MQW semiconductor laser,
A multi-stripe semiconductor laser or the like can be included.

[0012]

In the electrode for the light emitting / receiving element of the present invention, p
A p-type diamond-based carbon layer or a p-type β-type SiC layer is formed on the type II-VI group compound semiconductor crystal layer,
Further, a metal layer is formed on it. The energy level of the valence band of diamond or the like is about 1.3 eV deeper than the Fermi level of gold, which constitutes the metal layer. Further, it is almost equal to, for example, ZnSe which constitutes the II-VI group compound semiconductor crystal layer. Further, the diamond-based carbon layer or the β-type SiC layer can be made into a p-type conductive layer having a high carrier concentration by doping impurities. As a result, when holes are injected from the p-type diamond-based carbon layer or the p-type β-type SiC layer into the p-type II-VI group compound semiconductor crystal layer, no barrier is formed and ohmic contact can be obtained. . Further, the contact resistivity between the diamond-based carbon layer or the β-type SiC layer and the metal layer is on the order of 10 ⁻⁴ Ω · cm, and there is no problem.

Further, since the diamond-based carbon layer or the β-type SiC layer is composed of carbon or SiC having a high thermal conductivity, the electrodes are thermally stable and the temperature of the light emitting / receiving element during operation rises. Can be suppressed. Moreover, diamond-based carbon layer or β-type SiC
The layer is transparent to visible light. Therefore, when the electrode of the present invention is applied to a surface emitting type light emitting device, it is possible to avoid the problem that the light generated inside the light emitting device is blocked by the electrode emitted to the outside.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on embodiments with reference to the drawings.

(Embodiment 1) A light emitting device of Embodiment 1 whose schematic sectional view is shown in FIG. 1 is a surface emitting type light emitting diode. This light emitting device includes an n-type compound semiconductor substrate 10, a buffer layer 11 and an n-type clad layer 1 formed thereon.
2, active layer 13, p-type clad layer 14, p-type cap layer 20, insulating layer 30 for current confinement, p-type diamond-based carbon layer 21 made of diamond, metal layer 22, and n-type compound semiconductor substrate 10. And an n-type electrode 40 formed on the back surface of the. In the light emitting diode that is the light emitting element of Example 1, the light generated inside passes through the p-type diamond-based carbon layer 21 and is emitted to the outside. The light emitting diode which is the light emitting element of Example 1 can be manufactured by the steps described below.

As the n-type compound semiconductor substrate 10, for example, GaAs, GaP or InP can be used. The buffer layer 11 is formed by epitaxially growing InGaAs, InGaP, InAlGaAs or the like on the n-type compound semiconductor substrate 10 by the MOCVD method or the MBE method. ZnSe can also be used as the n-type compound semiconductor substrate 10. In some cases, the buffer layer 11 may not be formed.

Next, the n-type cladding layer 12, the active layer 13, the p-type cladding layer 14, and the p-type cap layer 20 are formed on the buffer layer 11 (in some cases, the n-type compound semiconductor substrate 10) by the MOCVD method or the MBE method. In order to grow epitaxially. Each of these layers is composed of, for example, the following combination II-VI group compound semiconductor crystal layers.

(Structural Example 1) Active layer: ZnSe Cladding layer: ZnMgSSe Cap layer: ZnSe, ZnSSe or ZnMgSSe (Structural example 2) Active layer: ZnSSe Cladding layer: ZnMgSSe Cap layer: ZnSSe or ZnMgSSe

After that, p forming the p-type cap layer 20 is formed.
The insulating layer 30 is formed on the type II-VI group compound semiconductor crystal layer by, for example, a sputtering method or a CVD method, and the insulating layer 30 is patterned into a desired shape by using a photolithography technique and an etching technique. The insulating layer is SiO ₂ , S
It can be composed of i ₃ N ₄ , Al ₂ O ₃ or the like.

Next, in the first embodiment, the p-type diamond-based carbon layer 21 made of polycrystalline diamond is formed on the p-type II-VI group compound semiconductor crystal layer constituting the p-type cap layer 20. It is preferable to polish the surface of the p-type cap layer 20 with diamond powder before forming the p-type diamond-based carbon layer 21 made of polycrystalline diamond in order to increase the density of diamond nucleus generation. P-type diamond-based carbon layer 21 made of polycrystalline diamond
Can be formed by, for example, an ECR plasma CVD method using CO gas or CH ₄ gas diluted with hydrogen gas as a source gas and diborane (B ₂ H ₆ ) as a dopant gas. As film forming conditions, for example, CH ₄ /
The molar ratio of B ₂ H ₆ / H ₂ is 0.005 / 0.00001 /
1. The pressure in the reaction chamber may be 230 Pa.

Alternatively, as disclosed in JP-A-4-266020, methane, carbon monoxide, ethanol, methanol, acetylene or the like is used as a carbon source, and nitrogen gas (N ₂ ) or ammonia is used as a nitrogen source. (N
H ₃ ), hydrazine (N ₂ H ₄ ) and nitrogen trifluoride (NF ₃ ).
Etc., and diborane (B ₂ H ₆ ) or boron carbide may be used as a boron source to form a film by the ECR plasma CVD method. The film forming conditions are, for example, CH ₄ / NH ₃ / B ₂ H ₆ = 1.
The reaction pressure may be 0/1/1 sccm and the reaction pressure is 10 ^-2 to 10 ^-1 Pa.

"Diamond deposition on silicon surface
s heated to temperature as low as 135 ° C ", M. Iha
ra, et al, Appl. Phys. Lett. 59 (12), pp 1473-147
The p-type diamond-based carbon layer 21 made of polycrystalline diamond can be formed by using the CVD method disclosed in 4, 16 September, 1991. That is, a filament is arranged above the p-type II-VI group compound semiconductor crystal layer that constitutes the p-type cap layer 20, and p
While heating the surface of the type II-VI group compound semiconductor crystal layer, for example, using CH ₄ / B ₂ H ₆ / H ₂ as a source gas, CVD
The p-type diamond-based carbon layer 21 can be formed by the method.

Alternatively, the p-type diamond-based carbon layer can be formed by a physical vapor deposition method such as an ion plating method or an ion beam sputtering method. When using the ion beam sputtering method, "Growth of diamond at
room temperature by an ion-beam sputter deposition
under hydrogen-ion bombardment ", M. Kitabatake, et
al, J. Appl. Phys. 58 (4), pp 1693-1695, 15 Augus
Ion beam sputtering using hydrogen ion bombardment may be employed as described in t 1985. A p-type diamond-based carbon layer made of polycrystalline diamond can be formed by ion-implanting or diffusing p-type impurities into the formed diamond layer.

Thereafter, if necessary, the p-type diamond-based carbon layer 21 is patterned. This patterning can be performed by a reactive ion etching method in which fluorine-based halogen is ionized and etched by ECR plasma or a direct etching method by a laser.

Thereafter, a metal layer made of, for example, Au is deposited on the p-type diamond-based carbon layer 21 by a sputtering method, and the metal layer 22 is patterned into a desired shape by using a photolithography technique and an etching technique. . Alternatively, after a metal layer made of Au / Ti is deposited by a sputtering method and subjected to alloying treatment in a forming gas, the metal layer 22 is patterned into a desired shape using a photolithography technique and an etching technique.
In this way, an electrode composed of the p-type diamond-based carbon layer 21 formed on the p-type II-VI compound semiconductor crystal layer 20 and the metal layer 22 formed thereon is formed.

Finally, on the back surface of the n-type compound semiconductor substrate 10, an n-type electrode 40 made of In or AuGe / Au is formed.
Are formed according to a conventional method.

(Embodiment 2) A light emitting element of Embodiment 2 whose schematic sectional view is shown in FIG. 2 is a semiconductor laser having an edge emitting double hetero structure. A light emitting device including this semiconductor laser includes an n-type compound semiconductor substrate 10, a buffer layer 11, an n-type clad layer 12, an active layer 13, a p-type clad layer 14, a p-type cap layer 20, and a current formed thereon. The insulating layer 30 for constriction, the p-type diamond-based carbon layer 21 made of polycrystalline diamond, the metal layer 22, and the n-type electrode 40 formed on the back surface of the n-type compound semiconductor substrate 10.
Consists of. In the semiconductor laser which is the light emitting device of the second embodiment, the light generated inside is emitted from the end face in the direction perpendicular to the plane of the drawing. The light emitting device of Example 2 is
It can be manufactured by a manufacturing method similar to that of the light-emitting element described in Embodiment 1.

(Example 3) In Examples 1 and 2, a diamond-based carbon layer 21 was formed on the p-type II-VI group compound semiconductor crystal layer 20. On the other hand, in Example 3, the p-type β-type SiC layer is formed on the p-type II-VI group compound semiconductor crystal layer. The structure of the light emitting element can be the same as the structure of the light emitting element described in the first and second embodiments.

The formation of the p-type β-type SiC layer on the p-type II-VI group compound semiconductor crystal layer is performed by, for example, SiH ₄ , C
It can be performed by an ECR plasma CVD method using a mixed gas of H ₄ , H ₂ and B ₂ H ₆ . Alternatively, it can be formed by a method of directly sputtering a SiC target in an argon atmosphere, or by vapor deposition of Si in a reactive atmosphere such as C ₂ H ₂ , sputtering vapor deposition, or ion plating. . SiC does not have to be 1: 1 in terms of chemical equivalent, and for example, Si / C of the SiC layer formed by the high frequency sputtering method is about 1.1 to 1.2.

Although the present invention has been described based on the preferred embodiments, the present invention is not limited to these embodiments. In the first and second embodiments, the diamond-based carbon layer has been described by taking diamond as an example.
It is also possible to form the diamond-based carbon layer from diamond-like carbon. In this case, diamond-like carbon may be formed by an RF plasma CVD method, an ion beam evaporation method, an ion beam sputtering method, a laser evaporation method, or the like.

The electrode of the present invention can be applied to a light emitting device having a semiconductor laser structure in which the active layer 13 has a multiple quantum well structure. In this case, the active layer, the clad layer, and the cap layer can be composed of compound semiconductor crystals having the following compositions. (Structural example 3) Active layer: ZnSe or ZnSSe (well layer) / Zn
MgSSe (barrier layer) Cladding layer: ZnMgSSe Cap layer: ZnSSe or ZnMgSSe (Structure example 4) Active layer: ZnCdSe (well layer) / ZnSe or Z
nSSe (barrier layer) Cladding layer: ZnMgSSe Cap layer: ZnSe, ZnSSe or ZnMgSSe

Alternatively, the electrode of the present invention can be used as a separate-confinement heterostructure (S).
It can also be applied to a light emitting device having a semiconductor laser structure having a CH) structure. In this case, the active region, the clad layer and the cap layer can be composed of a compound semiconductor crystal having the composition exemplified below. The active region is composed of the first light guide layer, the active layer, and the second light guide layer. (Structure example 5) Active layer: ZnCdSe Light guide layer: ZnSe or ZnSSe Clad layer: ZnMgSSe Cap layer: ZnSe, ZnSSe or ZnMgSSe (Structure example 6) Active layer: ZnCdSe Light guide layer: ZnSe, ZnSSe or ZnMgSSe Clad layer: ZnSSe Cap layer: ZnSe, ZnSSe or ZnMgSSe

The first and / or second light guide layer is
A so-called graded structure can also be used. That is, the active region of the light emitting element may have a GRIN-SCH structure.

Alternatively, the electrode of the present invention can be applied to an electrode of a light receiving element composed of a photodiode. In this case, the photodiode may have a structure similar to that of the surface-emitting type light emitting diode shown in FIG. Furthermore, the electrode of the present invention has a multiple quantum well structure (MQ
W) can be applied to the electrodes of the optical absorption modulator. In this optical absorption modulator, an electric field is applied perpendicularly to the well layer surface of the multiple quantum well structure. As a result, the quantum levels in the conduction band and the valence band change, and the shape of the wave function changes. As a result, the optical absorption spectrum of the multiple quantum well structure can be changed by applying an electric field.

[0035]

In the electrode for the light emitting and receiving element of the present invention, ohmic contact can be obtained with the p-type II-VI group compound semiconductor crystal layer, the driving voltage of the light emitting element can be reduced, and the p-type II can be obtained. It is possible to reduce the contact resistivity with the -VI compound semiconductor crystal layer. Further, it is possible to suppress the temperature rise of the light emitting / receiving element due to the improvement of the thermal diffusion characteristic. Furthermore, when the electrode of the present invention is applied to a surface emitting type light emitting element, it is possible to avoid the problem that the light generated inside the light emitting element is blocked by the electrode when emitted to the outside. The luminous efficiency of the device can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a light emitting device of Example 1.

FIG. 2 is a schematic cross-sectional view of a light emitting device of Example 2.

[Explanation of symbols]

10 n-type compound semiconductor substrate 11 buffer layer 12 n-type clad layer 13 active layer 14 p-type clad layer 20 p-type cap layer (p-type II-VI group compound semiconductor crystal layer) 30 insulating layer 21 p-type diamond-based carbon layer 22 metal layer 40 n-type electrode

Claims (3)

[Claims] 1. A II-V comprising a p-type diamond-based carbon layer formed on a p-type II-VI group compound semiconductor crystal layer and a metal layer formed thereon.
An electrode for a light emitting / receiving element made of a group I compound semiconductor. 2. A II-VI group compound comprising a p-type β-type SiC layer formed on a p-type II-VI group compound semiconductor crystal layer and a metal layer formed thereon. Electrode for semiconductor light emitting and receiving element. 3. A p-type II-VI group compound semiconductor crystal layer,
p-type ZnSe, p-type ZnSSe or p-type ZnMgSSe
The electrode for a light emitting and receiving element which consists of a II-VI group compound semiconductor of Claim 1 or Claim 2 characterized by the above-mentioned.