AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS3-ThM

Paper SS3-ThM4
Molecular Beam Epitaxy-Scanning Tunneling Microscopy of Wurtzite GaN Thin Films

Thursday, October 5, 2000, 9:20 am, Room 210

Session: Surface and Interface Structure II
Presenter: Q.Z. Xue, Tohoku University, Japan
Authors: Q.Z. Xue, Tohoku University, Japan
Q.K. Xue, Tohoku University, Japan
S. Kuwano, Tohoku University, Japan
K.F. Kelly, Tohoku University, Japan
S. Nakayama, Tohoku University, Japan
I.S.T. Tsong, Tohoku University, Japan
T. Sakurai, Tohoku University, Japan
T. Ohno, National Research Institute of Metals, Japan
Correspondent: Click to Email
Gallium nitride has been known for their enormous potential applications for optoelectronics devices operating in the spectral range from blue to ultraviolet. As the present application depends critically on controlled heteroepitaxy of GaN thin films, complete knowledge of its growth behavior and fundamental physical properties is highly desired to optimize its film growth and device applications. GaN can crystallize into both hexagonal and cubic forms, depending on the substrates and the growth conditions. And the hexagonal GaN has a further freedom in its film polarity, which has direct influence on its surface structure and growth process. In the present work, a systematic investigation of the growth and the surface reconstructions of the wurtzite GaN have been in-situ performed using molecular beam epitaxy (MBE) combined with scanning tunneling microscopy (STM) system. A two-step method is developed to prepare the 6H-SiC substrate, and the Ga-polar GaN(0001) and N-polar thin films are grown by plasma-assisted-MBE on the Si-polar and C-polar 6H-SiC respectively. Through the post-growth Ga-deposition, distinctly different series of surface reconstructions have been obtained on the films for each polarity, that is, on GaN(0001) surface, 1x1, 2x2, 4x4, @sr@7x@sr@7, 5x5, 5@sr@3x2@sr@13, 10x10 and 1x1-Ga fluid are formed, while on GaN(000-1) surface, 2x4, 6x6, 2@sr@7x2@sr@7 are observed. All these phases are Ga-rich, and no ordered N-rich phase has been observed. Based on the atomically-resolved STM images and first principles total energy calculations, we will show that the structures of these phases can be understood under Ga-adatom scheme. Since many of them are not satisfied with electron counting which is popular for the conventional semiconductors, we will document that stability of these phases can be interpreted by Peierls or Mott-Hubbard metal-insulator transitions due to the many-body effects.