高压强下GaN的结构相变及电子结构的第一性原理研究

First-principles Investigation of Structural Phase Transition and Electronic Structures of GaN Under High Pressure

基于密度泛函理论的平面波赝势方法,选择广义梯度近似(GGA)下的PBE算法-关联泛函对GaN晶体结构、能带结构以及电子态密度随压强的变化进行了研究,并计算出GaN材料的相变点压强值。研究结果表明:随着压强增加,常见的纤锌矿与闪锌矿GaN会发生结构相变成岩盐矿结构,并且其能带结构均由直接带隙转变成间接带隙。其中,通过焓相等原理得到纤锌矿到岩盐矿结构的相变压强为44.4GPa,而闪锌矿到岩盐矿结构的相变压强为43.6GPa。此外,随着压强增大,GaN纤锌矿、闪锌矿和岩盐矿的价带态密度均向低能方向偏移,而导带态密度向高能方向偏移,从而导致GaN共价性增强及带隙随压强增大而展宽。

This research is based on the plane wave ultra-soft pseudo-potential technology of density function theory. The crystal structure, band structure and electronic state density of GaN under high pressure were investigated by employing associated functional PBE algorithm within generalized gradient approximation （GGA）. The pressures of GaN near the point of phase transition also were calculated. The results indicate that with the increase of pressure, GaN in wurtzite and zinc blende structure can convert into rock salt structure under phase transition. Moreover, their band structures transform from direct band gap to indirect band gap. In the enthalpy equal principle, the transition pressure of GaN changes from wurtzite to rock salt phase is 44. 4 GPa, while it is 43.6 GPa for GaN changes from zinc blende to rock salt phase. In addition, with the increase of pressure, the density of states of valence band of GaN in wurtzite, zinc blende and rock salt structures move towards to low engery direction, while conduction band of it to high engery direction. For this reason, the increasing pressure enhances the covalence and increase the band gap of GaN.