JPH067601B2 - Light emitting element - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to improvement of a light emitting device having a MIS (Metal Insulator semi-conductor) junction.

[Technical background of the invention and its problems]

The MIS junction is adopted for a blue light emitting element in which it is difficult to obtain a good pn junction due to a large semiconductor band gap. However, in a semiconductor such as gallium nitride, selenium sulfide, zinc selenide, or silicon carbide used for such a blue light emitting element, it was difficult to form a good insulating thin film corresponding to silicon oxide of a silicon semiconductor.

For this reason, recently, attempts to form an ultrathin film of an organic material on a semiconductor surface by the Langmuir-Blodgett method and use it as an insulator have been mainly conducted by J.
The group led by Professor J. Roberts is leading the process. The organic insulating film used for the MIS junction must have a sufficiently thin film thickness (usually around 100 Å or less) so that an electron or hole tunnel effect is generated, and no defects such as pinholes are required. . Furthermore, the trap level for trapping electrons and holes does not exist in the insulating film or at the interface between the insulating film and the metal or semiconductor, and the insulating film is not deteriorated by heat generated by energization and light emission. is necessary.

According to the report of Professor Roberts, the Langmuir-Projet film of cadmium stearic acid (hereinafter abbreviated as LB film)
In the GaP light emitting device using, the luminous efficiency increases with the film thickness of the insulating film, and even if the thickest 175 Å or more formed,
The efficiency seems to increase further, and the luminous efficiency decreases with time. He also said that in a GaP light-emitting device that uses an LB film formed of a copper phthalocyanine derivative as an insulating film, the luminous efficiency is maximized when the insulating film thickness is 40Å, and the efficiency is 8.6 × 10 ^-3 . Although it has been reported that a luminous efficiency comparable to that of a device using a pn junction was obtained, a film thickness of 40Å is also observed in a GaP light emitting device using SiO ₂ as an insulating film.

Of the two examples described above, cadmium stearic acid is unlikely to operate as an injection-type device based on the tunneling phenomenon of electrons due to its electric and light emission characteristics, and its luminous efficiency is low. On the other hand, the element using the copper phthalocyanine derivative is considered to operate as an injection type element, suggesting the possibility of application to the MIS junction of the LB film.
However, it has been observed that light emission changes with time, and further development of an insulating film having less thermal stability and trap levels is desired.

[Object of the Invention]

The present invention is intended to provide a light emitting device using an insulating film of an organic polymer compound formed by a vapor deposition method having higher thermal stability than an LB film.

[Outline of Invention]

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

The organic polymer formed by the above vacuum deposition method,
For example, polyimide, polyamide, epoxy resin, etc. can be mentioned.

Example of Invention

 Examples of the present invention will be described below.

Example 1 First, GaP was grown epitaxially on a single-crystal GaP substrate.
After forming the layer, the GaP layer was doped with sulfur and nitrogen, respectively.
Doped with ¹⁷ cm ^-3 and 10 ¹⁹ cm ^-3 . An indium electrode was previously formed on the back surface of the GaP substrate so as to form an ohmic contact.

Then, the GaP substrate was attached to a holder in a vacuum chamber in which two evaporation sources were installed. One of the evaporation sources is a test tube filled with pyromellitic dianhydride (PMDA),
The other evaporation source consists of a test tube filled with diaminodiphenyl ether (ODA). These test tubes are isolated by a heat shield plate, and individual heaters are installed in each. Then, the vacuum chamber was evacuated to 10 ^-5 torr and each test tube was
After heating to 0 ° C. ± 2 ° C. and depositing an insulating film of a polymer compound on the GaP layer of the GaP substrate, 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 arranged on the test tube. The deposition rate of the polymer compound under the above conditions is 10 nm / min. The PMDA and ODA are raw materials of polyimide, and a polyimide insulating film was formed on the GaP layer of the GaP substrate by heat treatment. The main component of this polyimide is
Confirmed by infrared absorption spectrum.

Then, all electrodes were formed by vacuum evaporation on the polyimide film (thickness 10 nm) formed by evaporation for 1 minute. A MIS junction EL element of Au / polyimide / n-GaP was manufactured by such a series of methods.

When a voltage of 3 V was applied with the Au electrode side of the obtained FL element being positive, yellow-green light emission was observed under the Au electrode.
The current during light emission was -100 mA. The EL spectrum had a sharp peak near 590 nm.

Example 2 Instead of PMDA and ODA, benzophenonetetracarboxylic acid dianhydride and benzenetetracarboxylic acid dianhydride were used as acid anhydrides, diaminonaphthalene and p-phenylenediamine were used as diamines, and GaP was prepared in the same manner as in Example 1. Vacuum deposition, heat treatment polyimide film is formed on the GaP layer of the substrate,
Further, when an EL device having an Au electrode formed was manufactured, the same luminescence as in Example 1 could be observed.

Example 3 As raw materials to be vapor-deposited, terephthaloyl chloride and 4,4 ′ were used.
In the same manner as in Example 1, using diaminodiphenyl ether (or p-phenylenediamine),
An EL element was manufactured by vacuum vapor deposition on the aP layer, heat treatment to form an aromatic polyamide thin film, and further forming an Au electrode.
Light emission similar to that in Example 1 could be observed.

Example 4 As raw materials to be vapor-deposited, bisphenol A and 2,2-di [4-1,2 [-epoxypropyl) oxyphenyl] propane (a reaction product of bisphenol A and epichlorohydrin) and a small amount of melamine (catalyst) were used. In the same manner as in Example 1, vacuum deposition and heat treatment to form an epoxy resin thin film,
Further, when an EL element was manufactured by forming an Au electrode, the same light emission as in Example 1 could be observed.

〔The invention's effect〕

As described above in detail, according to the present invention, it is possible to provide a light emitting device which is extremely excellent in light emission efficiency and safety.

Claims (1)

[Claims] 1. A light emitting device having an MIS junction in which a metal, an insulating film and a semiconductor are bonded, wherein an insulating organic polymer compound synthesized by a vacuum deposition method is used as the insulating film.