Quantitative low-energy electron diffraction analysis of the GaN (1 × 1) reconstruction

The atomic structure of the GaN ( 000 1 ¯ ) (1 × 1) reconstruction was investigated by quantitative low-energy electron diffraction (LEED). The GaN ( 000 1 ¯ ) surface was annealed in an NH3 atmosphere and cooled down without any NH3 flux. LEED patterns with 6-fold symmetry were measured after annealing. The diffraction symmetry was explained by the presence of two domains on the GaN surface. LEED intensity–voltage (I–V) curves were acquired up to 500 eV and calculated in the framework of the dynamical theory of electron scattering. Good agreement between the experimental and theoretical curves was achieved for the bare GaN ( 000 1 ¯ ) (1 × 1) surface. Relaxation of the surface atomic layers decreased Pendryʹs R-factor to 0.21 ± 0.03. The plane relaxations derived from the LEED analysis were found to be in qualitative agreement with ab initio calculations. By using previously suggested models with adlayers on the bare GaN ( 000 1 ¯ ) (1 × 1) surface, much worse R-factors were obtained. It was concluded that the measured LEED I–V curves could be used to determine the bare GaN polarity.