Interplay of Native Point Defects with ZnO Doping Leonard J. Brillson, Ohio State University Research Foundation, DMR 0803276.
ZnO is a leading candidate for next generation opto- and microelectronics. We have used pulsed laser deposition (PLD) to grow degenerately Ga-doped ZnO (GZO) with near state-of- the-art carrier densities for transparent conducting oxides (TCOs) . We used depth-resolved cathodo-luminescence spectroscopy (DRCLS) to measure the Zn vacancy-related (VZn-R) native point defects in GZO vs. Hall-effect carrier density nHall. The figure shows that the strength of optical emission corresponding to isolated VZn and VZn clusters decreases as nHall increases. Ga diffuses into VZn sites at low temperatures during PLD growth, forming Ga-on-Zn-site donors (GaZn) and removing VZn acceptors. A 200ºC growth temperature maximizes Ga diffusion into Zn sites while minimizing Ga diffusion out of Zn sites, which increases at higher (>400ºC) temperatures. The interplay between native point defects and dopants suggests a new avenue for controlling doping.
Normalized Zn vacancy-related VZn-R native point defects in degenerately Ga-doped PLD-grown ZnO vs. nHall. This defect emission decreases dramatically as Ga atoms move into Zn vacancies, removing VZn acceptors and creating GaZn donors. Inset: Ga atoms in the ZnO lattice moving into Zn vacancy sites at low temperatures and moving out of Zn sites at higher temperatures, segregating to GZO interfaces as measured by depth-resolved X-ray photoemission.
High school women interns, from left to right: Asia Cunningham, Carly Green, Jessica Greer, Jasneet Singh, and Katelyn Lennon following the end-of-summer presentation of their research results. Second row left to right: Ohio State Prof. Leonard Brillson, Columbus School for Girls’ science teacher and liaison Dr. Kevin Sweeney, and Ms. Jemma Giddings, CSG Upper School Director.
Ms. Jasneet Singh ,a rising high school senior, and postdoc Snjezana “Snow” Balaz working in Prof. Brillson’s lab with an ultra high vacuum chamber, glancing incidence electron gun, and monochromator for DRCLS . Jasneet and Snow measured the type and depth of native point defects within the outer few atomic layers of oxide single crystals. They found major growth – dependent differences in the type of native point defects in the ZnO and SrTiO3 substrates used to grow most complex oxides. These defects then strongly influence interface electrical measurements.