GaN compound semiconductors, both electro-optical (LEDs,VCELs, etc.) and electronic ICs, are understood to be the next generation of higher performance solid-sate capability. In electronic applications this means new types of MOSFETs, Memories, Bipolar ICs, Power ICs, RF, Microwave and Milimeterwave devices, to name a few, that will work faster, in harsher conditions, with more bandwidth, more efficiently and with lower power. In the LED industry it means the advent of High Brightness low wavelength devices that will be applied to markets and product applications heretofore totally unattainable, including digitally compatible general “White ”lighting and big screen full-color solid-state outdoor video displays.

GaN is the only crystal, the fundamental ingredient of a semiconductor, with bandgap characteristics specifically advantageous for many visible short wavelength and ultraviolet LED applications. Bulk GaN cannot be grown by itself as a semiconductor crystal in a cost-effective manner yet, mostly because of physical constraints. Indeed, a major difficulty in growing high-quality GaN crystalline films was in establishing a suitable substrate material.

GaN was first successfully produced for High Brightness LEDs via MOCVD epitaxy on Al₂O₃ (Sapphire) and this combination continues today in large scale production from an increasing supplier base. Subsequently, GaN LEDs have also been produced on SiC (Silicon carbide) substrates as well and are currently in large scale production, albeit with somewhat lower brightness results. Other materials as well, each selected by device designers (both photonic and/or electronic) that base their selection upon the individual materials ’physical properties, are also in development for both LEDs and electronic components. For High Brightness LEDs, the current production platforms are Sapphire and Silicon Carbide, which are compared in the following table:

What goes into the selection of any material for any given semiconductor application are the basic material properties cited above in conjunction with the specific material required for deposition and crystal growth. In addition, other factors not cited above and exhibited by the substrate materials or based upon observation and/or development of various fabrication processes, also play a key part in substrate or superstrate material selection. III-V nitride semiconductors, such as InGaN, exhibit wurtzite (hexagonal lattice) crystal structure with tetrahedral bonding to next neighbors and a direct energy bandgap particularly useful for LEDs in the short wavelength regions. While SiC has a lattice mismatch to GaN of 3.5%, and between Al₂O₃ the mismatch is 13%, the mismatch, combined with differences in thermal expansion, was resolved by buffer layer deposition processes now used in large scale production. Other undesirable factors too have been reviewed and work-arounds implemented to resolve them, creating very effective results especially in LEDs. Additional observations, that have been part of this High Brightness LED semi-conductor design engineering process, are listed below:

Others Substrates: Silicon, Diamond, Gallium Nitride, GaAs, ZnO, Spinel (MgAl₂O₄), Lithium Gallium Oxide and other materials have been used to work with GaN or are in development. Some of this work encompasses LEDs. The potential for homoepitaxy with GaN wafer substrates would virtually eliminate lattice mismatch characteristics, for example, and is under development at many centers throughout the world. ZnO provides only a 2.2% lattice mismatch with GaN and is matched with InGaN. InGaN/ZnO, as well, is being worked with for use in LEDs by yet another cadre of research centers, both public and private.

Each material type posses unique combinations of physical, mechanical, chemical, thermal, electrical, optical, availability and economic characteristics. Frequently it is the combination of three or more of a materials' characteristics that make it the material of choice for a given semiconductor application. Electronic ICs, such as a Power FET, or an optoelectronic device such as a UV Photodetector, have different design criteria, hence different material combinations for each of them may provide the most optimum result. Research and improvements will continue to be pursued with breakthroughs established and used along the way.

UNIROYAL is unique in its business and technical approach to GaN, and its product implementation work, which includes: high volume production of InGaN/Al₂O₃ LEDs at UNIROYAL Optoelectronics, and the high volume production of 6H &4H SiC substrates, SiC Epitaxial products and is conducting work supplying fabricated digital, analog and high-frequency electronic devices at UNIROYAL Sterling Semiconductors.