Al_xGa_(1-x)As:Si中DX中心的双极化子机制及统计分析

Bipolaron mechanism of DX center in Al_x Ga_(1-x)As:Si

基于极化子和双极化子的物理图像,采用无拟合参数的巨正则统计方法计算了Si掺杂的AlxGa1-xAs的导带载流子浓度,计算得到的理论结果从高温到低温都与实验结果定量一致.计算证实了AlxGa1-xAs:Si中的DX中心的基态DX-是电子-晶格相互作用产生的负电双极化子.处于热平衡状态时,施主Si在AlxGa1-xAs中除了电离状态,处于不同晶格构型的单、双极化子态共存,低温时双极化子态被冻结;光照下发生持续光电导时,双极化子态变成单极化子态同时向导带释放一个电子,此过程伴随着进一步的晶格弛豫.理论与实验的对照说明单电子局域的DX0态在热平衡时并不能稳定存在,这和提出的双极化子机制是完全一致的.

The free-carrier concentration in Si-doped AlxGa1-x As has been calculated by grand-canonical-ensemble statistics without any fitting parameters.Our results are quantitatively in agreement with various experimental data in the temperature range 77—300 K,which indicates that the physical picture of the ground state of DX center（DX-） is of an electronic bipolaron due to the interaction between excess electrons and lattice.When exposed to light,one bipolaron can turn into a polaron,meantime release one electron to the conduction band accompanied by lattice relaxations.Our calculations also prove that DX0 is unstable at thermal equilibrium,which further confirms our bipolaron mechanism.