First-Principles Study Of Al_xGa_1-xSb Ternary Mixed Crystals

Gallium antimonide (GaSb), which have many advantages, such as low melting point, high electron mobility and photoelectric conversion rate, compared with GaAs, and the zinc blende lattice of GaSb is well lattice-match to other III-V mixed crystal systems. Especially, the bandgap of ternary mixed crystal AlxGa1-xSb can be adjusted by changing the Al component to produce optoelectronic device. In order to better understand nature of the ternary mixed crystal of AlxGa1-xSb, in this paper, the physical properties of the GaSb, AlSb, InSb and ternary mixed crystal AlxGa1-xSb (0≤x≤1) were studied by using the first-principles calculation using plane-wave ultrasoft pseudo-potential method based on the density functional theory.The results show that, GaSb, AlSb and InSb are direct bandgap semiconductors after structure optimization, their energy band structures are divided into the lower, middle and the upper valence band and conduction band. We also calculated the complex dielectric function, complex refractive index, reflectance and loss spectroscopy of these materials, and the specific heat, entropy, enthalpy and free energy as functions of temperature from 0 to1000K. The constant-volume specific heat varying with temperature followed Dulong-Petit Law.Further, based on the structural optimization, we studied electronic structure and optical properties for the ternary mixed crystal AlxGa1-xSb material. By calculating total energy and formation energy of AlxGa1-xSb under different Al component, obtained lattice constant of AlxGa1-xSb and compared with experimental data. Then we researched the electronic structure of AlxGa1-xSb, given the bandgap, band structure and density of states. The results show that, the bandgap of AlxGai-xSb increases with Al component increases, and the band structure divided to four parts. Combination with density of states, the electronic states intensity of Al-3p13s2 gradually increased, and Ga-3d104s24p1 electronic states of intensity gradually weakened, causing the bottom of conduction band move to high-energy range and the bandgap widened. Finally, based on the electronic structure calculations, we also calculated the complex dielectric function, the high-frequency dielectric constant, static dielectric constant and absorption spectra of AlxGai-xSb material for different Al component. We found that the high-frequency and static dielectric constant were decrease with increased of Al component, a blue-shift of the optical absorption spectra was observed, that is anti-Stokes phenomenon, the results obtained agree well with the experimental and other theoretical value.