Electron Spectroscopies of III-Nitride Semiconductors

Rudra P. Bhatta

Department of Physics and Astronomy
Georgia State University
Atlanta GA 30303

Growth of wurtzite GaN(0001) thin films by metalorganic chemical vapor deposition (MOCVD) may produce either Ga- or N-polar surfaces resulting in differences in surface termination, electronic structure, and chemical reactivity. GaN surfaces of both polarities have been characterized, in particular by their reaction with atomic hydrogen and deuterium. Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED) showed that the surfaces were clean and well ordered. High Resolution Electron Energy loss Spectroscopy (HREELS) was used to characterize the vibrational properties of the surfaces. HREELS following exposure to atomic hydrogen (deuterium) revealed surface N-H (N-D) and showed no sign of surface Ga-H (Ga-D) species. In contrast, HREELS of the Ga-polar surface following exposure to atomic hydrogen (deuterium) reveals Ga-H (Ga-D) stretching vibrations along with combination modes, but no N-H (N-D) vibrational modes are observed. Hydrogen is desorbed completely from this surface below 400o C.
In addition, we have characterized the elemental composition of InN films grown by HP-CVD. As grown InN samples contain carbon and oxygen contaminants, but after cleaning by sputtering for several cycles most of the carbon is removed from the surface. However, some carbon and oxygen impurities are incorporated in the film during growth. Films with less carbon and oxygen impurities exhibit an indium to nitrogen ratio closer to the ideal 1:1 for InN.