HEMT Material Technology and Epitaxial Deposition Techniques

Abstract

Compounds like gallium nitride (GaN), aluminum nitride (AIN, indium nitride (InN) and their alloys form a unique material system termed as nitride semiconductors. When compared to most of the other material systems, a much wider spectrum of bandgaps is covered by the nitrides. This is illustrated in Figure with the help of a bandgap-lattice constant plot. Nitrides have been researched by several research groups for more than three decades; it started when the first GaN-based light-emitting diode (LED) was reported by Pankove et al. The intrinsic material properties did not drive the performance of these early devices; instead, high-defect density and poor surface morphology of the heteroepitaxial films dictated the performance of these nitride semiconductor devices. The work done by Isamu Akasaki at Nagoya and Meijo Universities and Shuji Nakamura at Nichia Chemical Company in Japan during the mid-1980s did go a long way in mitigating such performance issues. Using AIN or GaN nucleation layers, metal-organic chemical vapor deposition (MOCVD) has been used to grow GaN films of high quality on sapphire substrates. This has led to an explosion in the field of GaN research in optoelectronics and gradually moved into electronics. Using the nitride semiconductor family of materials, blue, white, green and violet LEDs (along with blue-light semiconductor) lasers were fabricated by Shuji Nakamura, who currently a professor at the University of California at Santa Barbara. Owing to all the work that has happened to date, a very large number of applications starting from traffic light to large displays and high-definition DVD players make wide use of such nitride-based optoelectronics.