AVS 51st International Symposium
    Semiconductors Tuesday Sessions
       Session SC-TuP

Paper SC-TuP2
Comparison of Ga- and N-polar GaN Surfaces

Tuesday, November 16, 2004, 4:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: R.P. Bhatta, Georgia State University
Authors: R.P. Bhatta, Georgia State University
B.D. Thoms, Georgia State University
C.R. Eddy, Jr., Naval Research Laboratory
R.T. Holm, Naval Research Laboratory
R.L. Henry, Naval Research Laboratory
Correspondent: Click to Email
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 ordered. Electron Energy Loss Spectroscopy (EELS) and High Resolution Electron Energy loss Spectroscopy (HREELS) were used to characterize the electronic and vibrational properties of the surfaces. After cleaning the N-polar surface by sputtering with 1 keV nitrogen ions and annealing to 900 @degree@C, HREELS showed Fuchs-Kliewer phonons, N-H stretching vibrations, and combination losses, which indicate that hydrogen is present on the surface after annealing. HREELS following exposure to atomic hydrogen (deuterium) confirmed the assignment of surface N-H (N-D) and showed no sign of surface Ga-H (Ga-D) species. In addition, heating to temperatures from 400 to 900 @degree@C was not sufficient to remove the surface N-H species. In contrast, HREELS of the Ga-polar surface after sputtering and annealing showed Fuchs-Kliewer phonons but not any adsorbate loss peaks, which indicates a hydrogen-free surface. HREELS 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 400 @degree@C. In addition to differences in surface termination and chemical reactivity, EELS was used to characterize differences in the electronic structure of the hydrogenated Ga- and N- polar surfaces.