AlxGa1-xN氮化物结构和热力学性质的第一性原理研究

为了掌握Ⅲ族氮化物微观结构对热力学性能的影响规律,进而为超高功率器件的设计提供数据支持,本文借助第一性原理计算软件CASTEP,对半导体Al_xGa_1-xN不同合金结构及其热性能进行了系统研究。结构优化和数据分析后发现,Al_xGa_1-xN的晶格常数、平均键长和晶格热容值随Al组分值x(原子数分数)增大而线性减小。热力学性质计算结果表明,在GaN中引入Al组分会在频率带隙中引入杂质模,随着Al组分浓度的增加杂质模变宽并进入低频段,在低频段顶部频率随Al组分增大而线性升高,在12.5%以上低频段顶部频率均大于 (1/2)A₁(LO)。温度从300 K到700 K变化时, 合金热容随温度变化关系结果证明,在确定温度时,Al_xGa_1-xN合金热容随Al组分增大而线性减小。本文的研究为以Al_xGa_1-xN为代表的Ⅲ族氮化物半导体高功率器件设计提供了一定的设计参考。

First-Principle Study on Structure and Thermodynamics Properties of AlxGa1-xN Nitride

With the help of CASTEP first-principles calculations, the different doping structures and thermal properties of the semiconductor Al_xGa_1-xN were carefully studied for better understanding the influence of the microstructure on the thermodynamic properties in group Ⅲ nitrides, and then provide data support during the design processes of ultra-high power devices. After the optimization of Al_xGa_1-xN structures, with the increase of Al composition (atomic fraction), the lattice constant, average bond length and lattice heat capacity linearly decreases. The calculation of properties results indicate that the introduction of Al component in GaN will introduce an impurity mode in the frequency band gap. As the concentration of Al component increases, the impurity mode widens and enters the low frequency range. The top frequency of the low frequency band increases with the increase of Al composition, and the top frequency of the low frequency band above 12.5% is larger than (1/2)A₁(LO). From 300 K to 700 K, at the fixed temperature, with the increase of Al composition, the heat capacity of Al_xGa_1-xN alloy linearly decreases. The result in this paper provides a useful reference for the design of Ⅲ-nitride semiconductor high-power devices, such as Al_xGa_1-xN.