Structure and Properties of AlN and InN Surfaces and Defects

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Technical: Although nitride semiconductor materials are being used in some electronic and photonic applications including heterostructure field-effect transistors and blue light emitters, defects, impurities, and surface issues are hampering new applications such as the use of increasingly higher aluminum content AlGaN alloys for ultraviolet light emitting diodes and lasers and the development of InN-based transistors for terahertz emitters. This project aims to address these materials science issues through a tightly coupled experimental and computational effort. High quality AlN, InN, and their alloys are grow epitaxially and the high quality samples enable detailed characterization of surfaces, point defects, and impurities using structural, electrical, and optical techniques. Electron accumulation layers on the surface are investigated and controlled. The limits of n-type and p-type doping will be pushed. The experimental effort is directly tied to state-of-the-art first-principles calculations based on density functional theory; the "band-gap problem" will be addressed through the use of techniques that have recently successfully been implemented, such as quasi-particle calculations and hybrid functionals. Deep (localized) and shallow (extended) levels of defects and impurities are investigated, as well as surface reconstructions and surface states. Closing the loop between theoretical and experimental results is expected to provide deep understanding of fundamental atomic-level mechanisms and phenomena associated with synthesis and processing of these novel materials. Non-technical: This project addresses basic research issues in a topical area of materials science with high technological relevance. The wide-band-gap semiconductors that are the focus of the investigation are recognized as the prime materials for light emitters throughout the visible and into the ultraviolet, and the transition to solid-state lighting will have tremendous impact both in the developed as well as the developing world. Nitrides are also starting to gain ground in the area of high-frequency devices, with applications in telecommunications and radar. Another area of high potential impact is for photovoltaics, where the nitride materials systems can span the range from ultraviolet to infrared. This project has significant educational value: the graduate students are involved in a tight collaboration between theory and experiment. In addition, the computational project will make use of the brand new Allosphere facility at the California Nanosystems Institute at UCSB. The Allosphere is a 3-story-high spherical space in which a fully immersive and interactive virtual environment can be experienced. It will be helpful with the visualization and understanding of wave functions and bonding environments in the various materials, as well as with the dissemination of results to a broad audience.