Electronic Performance Study Of Chemically Ordered Al_x Ga_1-x N Alloys

Wurtzite GaN and its alloys, such as Al_xGa_1-xN,In_xGa_1-xN, have been viewed as the promising materials and widely used in the development of blue-ultraviolet optoelectronic devices including light-emitting diodes and laser diodes because of their advantages including the thermal stability and the tunable emitting wavelength. In particular, Al_xGa_1-xN alloys have attracted much attention due to their applications for ultraviolet and deep ultraviolet optoelectronic devices. In order to obtain an efficient ultraviolet light source, the control of Al composition and the improvement of crystal quality for Al_xGa_1-xN alloys are essential and necessary. The fabrication of devices needs band gap engineering. The band gap engineering allows band-gap from 3.44 eV for GaN to 6.28eV for AlN by controlling x of Al_xGa_1-xN alloys. To achieve the physical parameters in single system by controlling x of chemically ordered Al_xGa_1-xN alloys, the material of the ultraviolet photoelectric devices covering range from blue to deep ultraviolet light should be prepared, so chemical ordered Al_xGa_1-xN alloy became a hot topic. With the development of chemically ordered Al_xGa_1-xN alloys and the detection technology, the theoretical analysis of the properties of chemically ordered Al_xGa_1-xN alloys cannot only rely on the empirical parameters method. Therefore, the analysis of the properties of chemically ordered Al_xGa_1-xN alloys and the phenomena in the devices fabricated by chemically ordered Al_xGa_1-xN alloys need to be studied on basis of the full quantum theoretical methods. So the first principle methods was used to study chemically ordered Al_xGa_1-xN alloys.First-principles calculations have been carried out to study the chemically ordered Al_xGa_1-xN (0<x<1) alloys. The results showed that with increase of x (0<x<1), the lattice parameter of chemically ordered Al_xGa_1-xN alloys decreased, and the stability increased from view of energetic point. Perfect GaN and AlN are more stable that chemically ordered Al_xGa_1-xN alloys. It is more likely to form chemically ordered Al_xGa_1-xN alloys when the alloys approximation to perfect GaN and AlN. The calculated electronic structure demonstrated that chemically ordered Al_xGa_1-xN is still direct-gap semiconductor, and the band-gap of chemically ordered Al_xGa_1-xN alloys was increased with increasing x (0<x<1). The effects of ordering on band gap may be due to localization of quantum-well-like states, and the bond of chemically ordered Al_xGa_1-xN alloys was covalent bond with strong ionic characteristics. The simulation results of chemically ordered Al_xGa_1-xN alloys are significantly helpful for the growth of this alloys. And the results have certain reference value for the device which made of chemically ordered Al_xGa_1-xN alloys.