JPS61226978A - Light-emitting element - Google Patents

Abstract

PURPOSE:To improve luminous efficiency and stability by using an organic high molecular compound, which has mechanical and thermal strength higher than an LB film and is formed through a vacuum deposition method, as an insulating film for a MIS junction. CONSTITUTION:A GaP layer is formed onto a single crystal GaP substrate through epitaxial growth, sulfur and nitrogen are each doped to the GaP layer, and an indium electrode is shaped previously onto the back of the GaP substrate so as to be brought into ohmic-contact. The GaP substrate is mounted to a holder in a vacuum tank to which two evaporating sources are fitted. When the vacuum tank is evacuated and heated and an insulating film consisting of a high molecular compound is evaporated onto the GaP layer on the GaP substrate and the GaP substrate is thermally treated, an insulating film composed of polyimide is shaped onto the GaP layer on the GaP substrate through heat treatment. Accordingly, a light-emitting element having remarkably excellent luminous efficiency and stability is acquired.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to MIS (Metal Instructor)
The present invention relates to improvements in light emitting devices using semi-conductor junctions.

[Technical background of the invention and its problems]

MIS junctions are used for blue light-emitting elements in which it is difficult to obtain a good pn junction due to the large forbidden band width of the semiconductor. However, in semiconductors such as gallium nitride, selenium sulfide, zinc selenide, and silicon carbide used in such blue light emitting devices, it has been difficult to form a good insulating thin film corresponding to silicon oxide of a silicon semiconductor.

For this reason, recent attempts have been made to form ultra-thin films of organic matter on semiconductor surfaces using Langmuir-Blodgett's method and use them as insulators, mainly in the J.
, J., and the group led by Professor Loparts is taking the lead. The organic insulating film used for MIS junctions must be sufficiently thin (usually around 100X or less) to create a tunneling effect for electrons or holes, and must be free of defects such as pinholes. . Furthermore, if there is no trap level that captures electrons and holes in the insulating film or at the interface between the insulating film and the metal or semiconductor, the insulating film will not deteriorate due to the heat generated by energizing and emitting light. ,is necessary.

According to the report by Professor Roberts, in a GaP light-emitting device using a Langmuir-Blodgett film (hereinafter abbreviated as LB film) of cadmium stearate, the luminous efficiency increases with the thickness of the insulating film, and the thickest formed layer is 175X or more. However, the efficiency appears to increase further, and the luminous efficiency decreases over time. The professor also proposed a GaP film using an LB film formed from a copper phthalocyanine derivative as an insulating film.
It has been reported that the luminous efficiency of the light emitting device reaches its maximum when the insulating film is 40 μm thick, and the luminous efficiency is 8.6XIO%, which is comparable to a device using a pn junction. However, a film thickness of 40X has also been observed in a GaP light emitting device using 5IO2 as an insulating film.

Of the two examples mentioned above, in the case of cadmium stearic acid, it is difficult to imagine that it operates as an injection type element based on the electron tunneling phenomenon due to its electrical and luminescent properties, and its luminous efficiency is also low. On the other hand, devices using copper phthalocyanine derivatives are considered to operate as injection-type devices, suggesting the possibility of application of LB films to MIS junctions. However, changes in light emission over time have been observed, and it is desired to develop an insulating film with even higher thermal stability and fewer trap levels.

[Purpose of the invention]

The present invention aims to provide a light emitting element using an insulating film of an organic polymer compound formed by a vapor deposition method that has higher thermal stability than an LB film.

[Summary of the invention]

As a result of intensive research to solve the above-mentioned conventional problems, the present inventors discovered that an organic polymer formed by a vacuum evaporation method has higher mechanical and thermal strength than an LB film as an insulating film for MIS bonding. By using the compound, we have discovered a light-emitting device with improved luminous efficiency and excellent stability.

The organic polymer formed by the above vacuum evaporation method includes:
For example, polyimide? Examples include lyamide, epoxy resin, and the like.

[Embodiments of the invention]

The present invention will be explained in detail below.

Example 1 First, a GaP layer was formed on a single crystal GaP substrate by epitaxial growth, and then the GaP layer was doped with 10 cm and 10 cnr of sulfur and nitrogen, respectively. Note that an indium electrode is previously formed on the back surface of the GaP substrate so as to form an ohmic contact.

Next, the GaP substrate was attached to a holder in a vacuum chamber in which two evaporation sources were installed. One evaporation source consists of a test tube filled with pyromellitic dianhydride (PMDA), and the other evaporation source consists of diaminodiphenyl ether (O
It consists of a test tube filled with DA). These test tubes are separated by a heat shield and each is equipped with an individual heater. Next, the vacuum chamber was evacuated to 10 torr,
Heat each test tube to 150°C ± 2°C, and
After depositing an insulating film of a polymer compound on the P layer, the GaP substrate was heat-treated at 190° C. for 1 hour. In this vapor deposition process, the amount of vapor deposition was controlled by opening and closing a shutter placed above the test tube. Note that the 0 nm vapor deposition rate of the polymer compound under the above conditions is /rrlin. The PMDA,
ODA is a raw material for polyimide, and it is heated through heat treatment.
A polyimide insulating film was formed on the GaP layer of the aP substrate. The main component of this polyimide was confirmed by infrared absorption spectrum.

Next, all electrodes were formed by vacuum evaporation on the polyimide film (thickness: 10 nm) formed by evaporation for 1 minute.

Through this series of methods, Au/polyimide/n-G
An aP MIS junction EL device was manufactured.

When a voltage of 3 cm was applied with the Au electrode side of the obtained EL cord facing positive, yellow-green light emission was observed under the Au electrode. The current during light emission was ~100 min. The EL light spectrum had a sharp peak around 590°C.

Example 2 In place of PMDA and ODA, benzophenonetetracarboxylic acid dianhydride and benzenetetracarboxylic acid dianhydride were used as acid anhydrides, and diaminonaphthalene and p- were used as diamines.
G in the same manner as in Example 1 using phenylenediamine.
When an EL device was manufactured by forming a vacuum-deposited and heat-treated polyimide film on the GaP layer of the aP substrate and further forming an Au electrode, it was possible to observe the same luminescence as in Example 1.

Example 3 Terephthalic acid chloride is used as the raw material to be deposited! =4
．． Ga
When an aromatic polyamide thin film was formed on the GaP layer of the P substrate by vacuum evaporation and heat treatment, and an Au electrode was further formed to produce an EL device, light emission similar to that in Example 1 could be observed.

Example 4 Bisphenol A and 2,2-di(4-(1,2-epoxypropyl)oxyphenyl) as raw materials to be deposited
Propane (a reaction product of bisphenol A and epichlorohydrin) and a small amount of melamine (catalyst) were vacuum-deposited and heat-treated in the same manner as in Example 1 to form an epoxy resin thin film, and then an Au electrode was formed to form an EL element. When manufactured,
Light emission similar to that in Example 1 could be observed.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to provide a light emitting element with extremely excellent light emission efficiency and stability.

Claims (1)

[Claims] 1. A light emitting device using an MIS junction in which a metal, an insulating film, and a semiconductor are bonded together, characterized in that the insulating film is an insulating organic polymer compound synthesized by a vacuum evaporation method.