Electronic structure and optical properties of nonpolar Ga0.75Al0.25N surfaces

In order to study the nonpolar Ga0.75Al0.25N surfaces theoretically, models of Ga0.75Al0.25N(1,0,−1,0) and (1,1,−2,0) surfaces are built. Surface morphology, surface energy, work function, band structure, density of state, and optical properties of the two nonpolar surfaces are calculated using first principle based on density function theory (DFT). Results show that the N atoms and Ga(Al) atoms are not in the same height for both Ga0.75Al0.25N(1,0,−1,0) and (1,1,−2,0) surfaces. The GaN and AlN bonds rotate with the N atoms outwards, and the length of GaN bond and AlN bond decrease compared with that of bulk. The surface energy values of Ga0.75Al0.25N(1,0,−1,0) and (1,1,−2,0) surfaces are 1.902 J/m2 and 2.014 J/m2 respectively. The work function values of Ga0.75Al0.25N(1,0,−1,0) and (1,1,−2,0) surfaces are 4.025 eV and 4.007 eV respectively. The absorption coefficients of nonpolar surfaces are lower than that of bulk Ga0.75Al0.25N. This work provides a theoretical basis for the design and preparation of Ga1−xAlxN photocathodes.