Al_x Ga_(1-x)As中DX中心的研究进展

Recent Advances on DX Center Problem in Al_x Ga_(1-x)As

(一)DX中心与能带结构的关系 原来Lang等认为DX中心是AlxGa1-xAs中施主杂质与空位形成的络合物。奇怪的是它的浓度与Al的成分x有关。最近的实验彻底澄清了这个问题。因为AlxGa1-xAs能带结构随x的变化,与GaAs能带结构随压力p的变化相似,如果DX中心与能带结构有关,改变压力p与改变组分x应有相似效果。Mizuta等首先发现,对GaAs加压力到20多kbar时,DLTS测量出现一个峰。他们认为这个就是DX中心对应的峰。

A new electron trap state SD was found by DLTS measurement under light illumination in Si doped A.lxGa1-xAs. This new trap energy level ESD is shallower than the DX center energy in the gap and the concentration of SD is comparable to that of DX centers. The emission activation energy Ec=0.20±0.05eV and capture activation energy Ec= 0.17±0.05eV. The SD DLTS peak has never been detected previously because under dark and thermal equilibrium condition most of the electrons occupy the deeper DX states and most of SD states are empty. However, when the sample is illuminated by light, electrons are excited to the conduction band and then re-captured by SD since the deeper DX states have a slower electron capture rate, thus a new DLTS peak corresponding to SD appears. Constant temperature capacitance transient C-t and transient C-V measurements were also used to further confirm the existence of SD states.