First Principles Study Of Photoelectric Properties Of Doped GaN And GaN/ZnO Interface

In this paper photoelectric properties of doped GaN and GaN/Zn O are mainly researched. Useing first-principles methods based density functional theory calculate the optoelectronic properties of model by the CASTEP which is in MS. The main findings are as follows:The inner reasons of wurtzite as stable structure and zinc-blende as metastable structure is that Ga-N bond of wurtzite is more stable than zinc-blende and the energy of wurtzite smaller than zinc-blende. In addition, wurtzite GaN have more wider conduct band so that its optical response is more wider. Optical properties of these two structures change with the energy, and can be divided into four are similar regions.These areas are analyzed in detail and provides the theoretical basis for design and application of GaN.Different dopant atoms have different effect on the photoelectric properties of GaN. Mg, Si, Al and In are used as dopant in this paper.(1) Mg provide the acceptor level near the top of valence band to form conductive holes, which is typical of the P-type semiconductor. The more Mg doping concentration, the higher formation energy can be, so the high-quality P-type GaN is more difficult to form. In addition, there is significant optical response in low energy and high energy region.(2) Fermi level of Si-doped GaN move into the conduction band, and provide the injected electronic, which form the n-type semiconductor. The formation energy of Si-doped GaN is negative and the formation energy of Mg-doped GaN is positive, so doping Si is easier than doping Mg. Besides thiere is a small amount of optical response in the low energy region.(3) Al-doped GaN and In-doped GaN are still direct band gap semiconductor, and the Fermi level do not move, and the band structure is similar to the pure GaN. They conform to Vegard’s law, former show an inverse relationship and latter show proportional relationship. The higher Al concentration, the bigger the band gap can be. And the higher In concentration, the smaller the band gap can be. So Al and In can regulate the GaN band gap value continuously, and get the continuous light band.(4) The band gap value of the pure and doped GaN increases with the increase of the stress, which make the optical constant blue shift. And their internal cause of the change of the band gap value is also analyzed in detail. Mg-doped GaN and Si-doped GaN began to appeare blue shift phenomenon when the energy higher than 5eV. But the pure GaN, Al-doped GaN and In-doped GaN began to appear blue shift phenomenon at the beginning of the optical response.Finally the electronic structure and optical properties of GaN, ZnO and GaN/ZnO is calculated and analysed. The results show that they are all direct band gap semiconductor material, and the static dielectric constant is almost the same. The top of valence band of GaN/ZnO is determined by the N 2p and O 2p, and the bottom of conduction band is determined by Zn 4s. Dielectric function of GaN/ZnO is between dielectric function of GaN and ZnO; the range of energy loss of GaN/ ZnO is the smallest but strength is the biggest; absorption spectrum of GaN/ZnO is between GaN and ZnO; the range of reflection response of GaN/ZnO is the smallest, but the strength is the biggest.