TITLE: "Aspects of hydrogen behavior in GaN: Mg-acceptor passivation/compensation and interaction with point defects"

SPEAKER: Dr. Alan F. Wright,

TIME: Thursday Nov. 29, 2001 at 4 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

Hydrogen can be incorporated into GaN during growth by metalorganic chemical vapor deposition and during post-growth processing steps needed to fabricate electronic and optoelectronic devices. Incorporation of hydrogen during growth of Mg-doped GaN is beneficial in that it passivates or compensates the Mg acceptors, thereby suppressing the formation of compensating nitrogen vacancies. After growth, the hydrogen must either be removed or neutralized in order to achieve hole concentrations needed for device operation. A major goal of our research is to understand hydrogen behavior in Mg-doped GaN, and specifically, its release during postgrowth annealing treatments. A broader goal is to understand how hydrogen interacts with the impurities and point defects thought to exist even in state-of-the-art GaN. The approach we are pursuing utilizes density-functional theory to determine defect atomic structures, zero-temperature formation energies, hydrogen vibration frequencies, and energy barriers for diffusion of mobile species. These quantities are used as input to a numerical model describing the coupled transport and reactions of impurities, dopants, defects and charge carriers, and the modeling results are compared with measurements to assess the extent to which currently recognized processes can account for hydrogen behavior. In this talk, I will describe in detail results pertaining to hydrogen behavior in p-type GaN:Mg. Notable conclusions from this work are that: 1) Hydrogen is highly soluble in this material, and 2) Hydrogen release during post-growth annealing treatments is impeded by a substantial surface barrier. I will also describe recent density-functional-theory results for hydrogen interacting with various point defects in GaN and discuss the pos sibilities for hydrogen passivation of point defects in GaN. This work was done in collaboration with S. M. Myers. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under Contract DE-AC04-94AL85000.