Active solid-state devices (e.g. – transistors – solid-state diode – Specified wide band gap semiconductor material other than... – Diamond or silicon carbide
Patent
1997-11-24
1999-02-23
Monin, Donald
Active solid-state devices (e.g., transistors, solid-state diode
Specified wide band gap semiconductor material other than...
Diamond or silicon carbide
257 84, 257103, 257461, 257 81, 438107, 438133, 438 68, 438 87, H01L 3300, H01L 29161
Patent
active
058747478
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a light emitting optical device capable of emitting light in the green-blue to ultraviolet spectrum, and more specifically semiconductor devices formed using gallium nitride, e.g., comprising a gallium nitride active layer on a silicon carbide substrate, as well as to a method for forming gallium nitride devices using silicon caribide substrates.
2. Description of the Related Art
UV and blue light emitters (both lasers and light emitting diodes (LEDs)) have a wide range of applications including high density optical storage, full color displays, color determination systems, and spectroscopic analysis sources. Electroluminescent semiconductor devices such as lasers and LEDs that emit light in the green-blue to ultraviolet region of the electromagnetic spectrum are correspondingly of great interest, but have not yet reached the levels of performance that are presently available in red and yellow light emitters, as measured by quantum efficiency and luminous intensity. The major reason for the deficiency of the blue light-emitting devices is the much less well developed state of the semiconductor materials that are suitable for blue light emission.
Only a few material systems are capable of directly producing solid state light emission in the blue/UV region of the electromagnetic spectrum--the II-VI compounds, silicon carbide, and the III-V nitrides.
Although the II-VI compounds such as ZnSe, ZnS, CdS, and their alloys are direct band gap materials and thus have high optical efficiency, such compounds are plagued by fuidametal material property deficiencies, including softness and low melting temperatures, which cause defects to be readily generated and propagated, in turn leading to poor reliability characteristics and short product life. Thus, while LEDs and lasers have been demonstrated in II-VI compounds, the lack of stability and the short lifetimes of the resulting devices are major shortcomings which have severely restricted their commercial potential and use. It has been demonstrated that the short lifetimes in II-VI devices result from the rapid propagation of defects throughout their active regions, which act as nonradiative recombination sites. These results are indicative of low temperature and room temperature characteristics. Operation at higher temperatures or at high power conditions will increase the degradation rate and exacerbate the problem. Additional problems with the II-VI materials include the necessity of using quaternary layers to achieve blue emission in relatively lattice-matched heterostructures. The simplest and most well developed materials are ZnSe, ZnS, CdS, and their alloys which produce emission in the blue-green region, about 500 nm. Other II-VI compounds could be used to produce emission in the blue and ultraviolet, for example alloys of ZnS and either ZnSe, CdS, CdSe or MnSe. However, these materials have not been well investigated and have other major problems including the lack of a simple latticematched heterostructure system and the lack of a suitable substrate.
Blue LEDs formed in silicon carbide epilayers on silicon carbide substrates have been reported (U.S. Pat. No. 4,918,497). However, silicon carbide is an indirect band gap material, and therefore radiative recombination is inefficient, and consequently these SiC-based light emitting diodes (LEDs) have poor optical efficiency. A commercially available 6H-polytype SiC LED with a peak light emission at a wavelength of 470 nm has an external quantum efficiency of 0.02% and performance of 0.04 lumens/watt (Cree Research, Durham, N.C.). This performance is quite low compared to the best LEDs emitting in the red (AlGaAs, 16% quantum efficiency and 8 lumens/watt) and yellow-green (AlInGaP, 1% quantum efficiency and 6 lumens/watt), where quantum efficiency is defined as the number of photons emitted per electron supplied X 100%, and luminous intensity is the luminous (visible) flux output of a light source measured in lumens divided by the electrica
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Redwing Joan
Tischler Michael A.
Advanced Technology & Materials Inc.
Hultquist Steven J.
Monin Donald
Zitzmann Oliver A. M.
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