SBIR-STTR Award

This SBIR proposal addresses the liquid phase epitaxy (LPE) of gallium nitride (GaN) films using nitrogen-enriched metal solutions. Growth of GaN from solutions offers the possibility of drastically reducing the density of line defects. As these defects adversely affect both breakdown voltages and electron velocities, their reduction can significantly increase the performance of high power Ka-band HEMT structures used for satellite communications. To achieve low defect densities in GaN films and efficient, large scale manufacturing, IIIAN will utilize new chemical growth methods based on nitrogen-enriched metal solutions, in particular the Ca-Ga-N ternary system. In the binary calcium-gallium alloy system it is possible to achieve a nitrogen atomic fraction of 2% at 900 oC and 2 bar. This is a significantly higher fraction than is possible in pure gallium solutions. For example, a temperature of ~1700 oC and pressure of ~10 kbar are necessary to achieve even 0.1% atomic nitrogen fraction in pure gallium solvent. Anticipated

Benefits:
Group III-nitride optoelectronics have become prevalent in commercial applications for shortwavelength blue and UV LEDs. Laser diodes made from this material system are still limited in lifetime by thermal degradation due to scattering effects IR-loss at line defects. The approach presented here for defect density reduction will benefit these commercial optoelectronics. This proposal addresses the specification stated in solicitation topic O1.07 for "Epitaxial GaN films with threading dislocations less than 106 per cm2 for use in space qualified wide band-gap semiconductor devices at X- and Ka-band." The goal of The IIIAN Company is to provide these low defect density GaN films on 6" diameter substrates as starting templates for subsequent growth of GaN/AlGaN HEMT structures. With the common epitaxial growth techniques for group III-nitrides, Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Vapor Deposition (MOCVD), line defects follow through from those in the initial buffer layer. By utilizing LPE to produce low defect density GaN films on 6" substrates, IIIAN will enable compound semiconductor manufacturers (i.e. RFMD, TriQuint, Anadigics) to better utilize the group III-nitride material system for the high frequency, high power SSPAs requested in this topic for future NASA missions to the moon and the planets.

The innovations proposed here are Ka-band (38 GHz) group III-nitride power FETs and the dislocation density reducing epitaxial growth methods (LPE) needed for their optimal performance and reliability. Ka-band power transistors with >60% Power Added Efficiency (PAE) are not commercially available. The primary limitations to their manufacture are lack of mature process technology at major GaN foundries for sib-100nm lithography necessary for gate definition, and the difficulty of obtaining low dislocation density GaN templates in a suitable wafer size format (3-inch SiC and 6-inch Si) for mass production. Demonstration of Ka-band operation in the group III-nitrides has, to date, been primarily the realm of academic research labs. IIIAN's proposal bridges the gap between commercially available nitride foundry capabilities and pure research by utilizing proven process technology at RFMD for processes not requiring deep, submicron lithography and utilizing state-of-the-art nanofabrication technology available at the University of Minnesota's NanoFabrication Center. Anticipated

Benefits:
Group III-nitride semiconductor technology for discrete transistors and MMICs has a wide range of applications for cell phones, wireless infrastructure (base stations), switching power supplies, and in high performance military electronics. Most of these applications are related to power amplification, but group III-nitrides having much higher breakdown voltages than other compound semiconductors like GaAs or InP also offer significant advantages for toughened, low noise receivers. Low dislocation density GaN films are also a necessity for long-lived blue and UV semiconductor lasers, and a more robust and cost efficient GaN template technology will directly impact the viability of solid state lighting. The proposed work is in direct response to the call in subtopic O1.07 in the 2009 NASA SBIR solicitation for "High-efficiency (> 60%) Solid-State Power Amplifiers (SSPAs), of both medium output power (10 W-50 W) and high-output power (150 W-1 KW), using power combining techniques and/or wide band-gap semiconductor devices at X-band (8.4 GHz) and Ka-band (26 GHz, 32 GHz and 38GHz)" and "Epitaxial GaN films with threading dislocations less than 106 per cm2 for use in space qualified wide band-gap semiconductor devices at X- and Ka-band." These calls for technical advancement are in turn directly related to high data rate communications with future NASA missions to the moon, to Mars, and to the outer solar system.