JPH0677546A - Light emitting element - Google Patents

Abstract

PURPOSE:To provide a light emitting element capable of stably emitting light extending over the wavelength band from the infrared to millimeter wave region. CONSTITUTION:A normal conductive metallic superconductor junction J2 is formed of a normal conductive metal 2 and a superconductor 3 so that a current in normal direction may be fed to said junction 2 for emitting light by the recoupling of the reflecting electrons e2 of this normal conductive metal 2 with outgoing holes h2. This normal conductive metallic superconductive junction J2 may be substituted with the junction formed of a semiconductor 1 and the superconductor 3. At this time, the recoupling probability can be increased by providing a potential well for accumulating electrons of holes in the semiconductor region. Besides, the electrons and the holes can be ballistically implanted by using Schottky junction J1 or hetero junction with any other semiconductor so as to equalize the energy of incident electrons for increasing the recoupling probability. Furthermore, the laser beams can be oscillated by providing a cavity around the light emitting region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element, and more particularly to a light emitting element which emits light stably in a wavelength band ranging from far infrared to millimeter waves.

[0002]

2. Description of the Related Art Conventionally, a direct transition type semiconductor device such as a light emitting diode has been widely used as a light emitting element which emits light continuously and has a stable light emission wavelength. In this light emitting diode, an electric current is applied to a pn junction of a semiconductor in a forward direction to recombine excess electrons and holes generated near the junction to emit light.

Further, in the structure of this light emitting diode, there is obtained a laser diode (LD) which realizes a strong population inversion and further confines the entire active region in an electromagnetic cavity to resonate oscillated light.

A semiconductor heterojunction is used for these light emitting elements or laser diodes (LD).
The emission wavelength λ is determined by λ = ch / Eg, where Eg is the band gap of the semiconductor, c is the speed of light, and h is the Planck constant.

[0005]

In the conventional light emitting device using the above-mentioned conventional semiconductor pn junction,
When a semiconductor having a band gap of about 1 eV is used, it is limited to light having a wavelength ranging from visible light to infrared light. Therefore, an object of the present invention is to provide a light emitting element that stably emits light in a wavelength band extending from far infrared to millimeter waves.

[0006]

In a light emitting device according to the present invention, a junction is formed by a normal-conducting metal and a superconductor, and a forward current is applied to the junction to generate electrons and holes in the junction. A structure is adopted in which the light is recombined to emit light.

Further, a structure is adopted in which a junction is formed by a semiconductor and a superconductor, a forward current is applied to this junction, and electrons and holes generated in this junction are recombined to emit light.

In this case, electrons or holes can be ballistically injected by using a Schottky junction or a heterojunction with another semiconductor.

Further, a cavity is provided around the joint,
Laser oscillation can be performed.

[0010]

According to the present invention, the material of the light emitting device is the junction of the normal conductive metal and the superconductor, or the junction of the semiconductor and the superconductor. FIG. 1 is an explanatory view of the light emitting principle of the light emitting device of the present invention. The principle of light emission of the light emitting element using the junction of the normal conductive metal and the superconductor of the present invention will be described with reference to this figure. In this figure, 1 is a semiconductor, 2 is a normal conductive metal,
3 is a superconductor, J ₁ is a Schottky barrier, J ₂ is a normal metal superconductor junction, e ₁ is an incident electron, e ₂ is a reflected electron, h
₂ is an outgoing hole.

In this figure, a semiconductor 1 and a normal conductive metal 2 are shown.
Minute Schottky barrier (junction) formed on the interface of J ₁
An electron e ₁ having an energy exceeding ₁ is formed at the interface between the normal metal 2 and the superconductor 3, and the normal metal superconductor junction J ₂
Is reached. The electrons no energy only beyond a Schottky barrier J ₁ is not incident unless tunneling Schottky barrier J _1.

[0012] This normal metal superconductor junction J₂Then enter
Electron e₁Form a Cooper pair in superconductor 3.
This is a normal metal superconductor junction J₂Incident from
Electronic e₁Backscattered electron e which is a part of₂Is reflected, and this
At the same time, the incident electron e₁Exit hole with opposite direction of motion to
h₂Is released.

This phenomenon is called Andreev reflection, and when a part of the incident electron e ₁ is changed to a Cooper pair in the superconductor 3, the conservation law of energy, charge and momentum in the superconductor 3 is used. This is a phenomenon in which holes are emitted so as to fill the holes. Although the ratio between Andreev reflection and normal reflection differs depending on the energy of the incident electron e ₁ , it is possible to make them the same order of magnitude.

Although this energy is relaxed through various scattering processes with time, the normal metal superconductor junction J
By causing a current to flow steadily perpendicular to ₂ , a region where electrons and holes coexist can be formed in the normal conductive metal. In such a state, when electrons and holes recombine spontaneously and emit an electromagnetic wave (light), this electromagnetic wave (light)
Acts on nearby electrons and holes to induce their recombination and emit electromagnetic waves (light). Then, this electromagnetic wave (light) again acts on electrons and holes in the vicinity to induce recombination, and a recombination is multiplied in an avalanche to generate a highly efficient light emitting action.

In the light emitting device of the present invention, as described above, since the energies of the reflected electrons e ₂ and the emitted holes h ₂ are almost the same and they are moving in the same direction, the electromagnetic wave ( Since the properties of the (light) direction, the polarization plane, etc. are almost the same, the generated electromagnetic waves (light) are less likely to cancel each other, and a highly efficient light emitting element is realized.

[0016] In this case, as described above, simply by merely applying a forward bias to the normal metal superconductor junction J _2, electron motion direction incident to the normal metal superconductor junction J ₂ is slightly Isotropic, reflected electron e ₂ and outgoing hole h ₂
There is some variation in the kinetic energy in the direction of the optical axis.

However, as shown in FIG. 1, for example, a Schottky barrier (junction) J ₁ is provided on the normal metal 2 side to make the thickness of the normal metal 2 shorter than the mean free path of electrons. By injecting electrons from the Schottky barrier (junction) J ₁ ballistically, an electron beam with more uniform momentum (energy) can be produced. At this time, when the electron beam reaches the normal metal superconductor junction J ₂ of the superconducting metal 2 and the superconductor 3, the reflected electron e ₂ and the emitted hole h ₂ form a beam in the same direction, and each reflected electron The energies of e ₂ and emitted hole h ₂ are the same.

In such a state, backscattered electrons e ₂
And the exit hole h ₂ can recombine with a higher probability and be converted into light having twice the energy of the original incident electron e ₁ and thus a steady emission in the far infrared region. Will be possible.

Unlike ordinary quasi-particle injection, Andreev reflection causes a current even for an incident electron e ₁ which is equal to or smaller than the energy gap of a superconductor, so that an arbitrary small energy which is not restricted by the energy gap. It is possible to emit light. A further advantage is that since the region in the k-space where electrons and holes are distributed is near the Fermi surface of the normal metal, the density of states is very high, the recombination probability is high, and the threshold value is low. A light emitting element can be realized.

Further, the uniformity of the momentum of the collective of electrons and holes described above makes the uniformity of the emission efficiency, monochromaticity, polarization property, etc. very high. This property is a particularly remarkable advantage when the light emitting device is configured as a laser.

In order to construct a laser with this light emitting element, it is necessary to use a conventionally known means such as cleavage, a reflective film such as a multilayer dielectric layer, etc., and to put the three-layer structure in the cavity. is necessary. From the above description, it is clear that the light emitting device of the present invention can form a strong population inversion even at a low current density. The laser device thus manufactured has a low threshold current and a high coherence.

In the above description, the junction formed by the normal conductive metal and the superconductor is used, but the junction formed by the semiconductor and the superconductor may be used.

[0023]

EXAMPLES Examples of the present invention will be described below. Figure 2
FIGS. 3A to 3C and FIGS. 3D to 3F are explanatory views of the manufacturing process of the light emitting device of one example. In this figure, 11
Is a semi-insulating substrate, 12 is a semiconductor layer, 13 is a normal conductive metal layer, 14 is a superconductor layer, 15 is a SiO ₂ film, 16 is a resist film, and 17 is a gold layer.

The structure and manufacturing process of the light emitting device of this embodiment will be described with reference to the manufacturing process explanatory diagram.

First step (see FIG. 2A) A semi-insulating substrate 11 made of GaAs and having a thickness of 300
A semiconductor layer 12 made of 0Å n-type GaAs is grown by a molecular beam epitaxy (MBE) method. A normal conductor metal layer 13 made of Au having a thickness of 500Å and a superconductor layer 14 made of Nb having a thickness of 3000Å are formed thereon by a vapor deposition method.

Second step (see FIG. 2B) A resist is applied on the laminate formed in the first step and patterned by a photolithography technique. Using the patterned resist film as a mask, ion milling is performed. By doing so, a part of the superconductor layer 14 made of Nb and the normal metal layer 13 made of Au is removed.

Third step (see FIG. 2C) After depositing the SiO ₂ film 15 on the entire surface by CVD, a resist is applied on the SiO ₂ film 15 and patterned into a shape having openings, and the patterned resist film 16 is formed. Using as a mask, the SiO ₂ film 15 is removed by etching with a dilute aqueous solution of HF / NH ₄ F to form an opening.

Fourth step (see FIG. 3D) A thickness of 3000 is formed on the entire surface of the resist film 16 including this opening.
Gold layer 17 is formed by vapor deposition of gold (Au).

Fifth step (see FIG. 3 (E)) By removing the entire resist film 16 with a resist stripping solution, the gold layer 17 on the resist film 16 is removed, and n-type G
The semiconductor layer 12 made of n-type GaAs, leaving the gold layer 16 directly formed on the semiconductor layer 12 made of aAs.
An ohmic electrode is formed on.

Sixth step (see FIG. 3F) A part of the SiO ₂ film 15 on the superconductor layer 14 is removed by ordinary photolithography and wet etching to draw out the anode electrode.

As described above, in this embodiment, instead of the junction formed by the normal conductor and the superconductor, the junction formed by the semiconductor and the superconductor can be used.

The incident electrons can be ballistically injected by using a semiconductor heterojunction instead of the Schottky junction, and a laser emitting device can be formed by providing a cavity around the junction.

[0033]

As described above, according to the present invention,
A light-emitting element that stably oscillates light in the wavelength band from far infrared to millimeter waves has been obtained, and it is practically used as an information propagation means body of light in this wavelength band, which is not currently used for information propagation such as communication. There is a big contribution.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a light emitting principle of a light emitting device of the present invention.

2A to 2C are explanatory views (1) of a manufacturing process of a light emitting device of one example.

3 (D) to (F) are explanatory views (2) of the manufacturing process of the light emitting device of the example.

[Explanation of symbols] 1 semiconductor 2 normal metal 3 superconductor J ₁ Schottky barrier J ₂ normal metal superconductor junction e ₁ incident electron e ₂ reflected electron h ₂ emitted hole 11 semi-insulating substrate 12 semiconductor layer 13 Normal conductive metal layer 14 Superconductor layer 15 SiO ₂ film 16 Resist film 17 Gold layer

Claims (4)

[Claims] 1. A light emitting device, characterized in that a junction is formed by a normal conductive metal and a superconductor, and a forward current is applied to the junction to recombine electrons and holes generated in the junction to emit light. 2. A light emitting device, wherein a junction is formed by a semiconductor and a superconductor, and a forward current is applied to the junction to recombine electrons and holes generated in the junction to emit light. 3. An electron or hole is ballistically injected using a Schottky junction or a heterojunction with another semiconductor, according to any one of claims 1 to 4. Light emitting device. 4. The light emitting device according to claim 1, wherein a cavity is provided around the joint to perform laser oscillation.