氮化镓相图预测及其高压熔化特性研究

Phase diagram prediction and high pressure melting characteristics of GaN

采用经典分子动力学模拟,结合第一性原理计算及晶格动力学方法对氮化镓(GaN)纤锌矿结构与岩盐结构在0—80 GPa压力范围内的相图进行了预测.第一性原理计算与分子动力学模拟得到的零温下GaN纤锌矿到岩盐结构的相变压力分别为44.3 GPa和45.9 GPa,与已有研究的实验结果吻合;通过外推纤锌矿结构GaN的熔化曲线得到其零压下的熔化温度为2295 K,当压力增大到33.3 GPa时,纤锌矿结构熔化曲线与岩盐结构熔化曲线相交,两种结构的熔化温度均随压力的增大而上升;GaN还可能存在超离子相,纤锌矿结构在压力大于2.0 GPa且温度高于2550 K时发生超离子相转变,岩盐结构在压力温度大于33.1 GPa和4182 K后发生超离子相转变,二者的相转变温度均会随着压力的增大而升高;GaN纤锌矿和岩盐结构的相界线并非为一直线,在高温下相界线斜率为正,随着温度的降低逐渐变为一条具有负斜率的曲线.

The Ⅲ-Ⅴ compound semiconductor,GaN,has become an excellent semiconductor material for developing the high-frequency and high-power electronic devices because of its excellent characteristics,including large band width,high thermal conductivity and fast electron saturation rate,and has received extensive attention in recent years.However,the decomposition temperature of GaN is lower than the melting temperature,some of its fundamental properties,such as melting temperature and high temperature phase transition pressure,are still unclear,and so,now the investigation of fundamental properties dominates the whole process of this material from development to mature applications.In the present work,the classical molecular dynamics simulations combined with the first-principles calculations and lattice dynamics methods are adopted to predict the phase diagrams of GaN with wurtzite and rocksalt structures in a pressure range of 0-80 GPa.The phase transition pressures,44.3 GPa and 45.9 GPa,obtained from the first-principles calculations and molecular dynamics simulations from wurtzite to rocksalt structure in GaN at zero temperature,are in agreement with the available experimental results(Sadovyi B,et al.2020 Phys.Rev.B 102 235109).The melting temperature at 0 GPa is 2295 K obtained by extrapolating the GaN melting curve of the wurtzite structure.With the pressure increasing to 33.3 GPa,the melting curve of wurtzite structure in GaN intersects with the melting curve of rocksalt structure,and the melting temperatures of both structures increase with pressure increasing.It is found that GaN may have a super ionic phase and the super ionic phase transition occurs in the wurtzite structure at pressures greater than 2.0 GPa and temperatures above 2550 K,whereas the rocksalt structure undergoes a superionic phase transition at pressures and temperatures higher than 33.1 GPa and 4182 K,respectively,and both of the phase transition temperatures increase with pressure increasing.The slope of the phase boundary line of GaN is positive at high temperatures and gradually changes into a curve with a negative slope as the temperature decreases.