调制掺杂Al_xGa_(1-x)N/GaN异质结中Al_xGa_(1-x)N势垒层表面态及其他局域态性质研究

Surface States and Other Local States in Al_xGa_(1-x)N Barriers of Modulation-Doped Al_xGa_(1-x)N/GaN Heterosturctures

通过测量调制掺杂Al0 2 2 Ga0 78N/GaN异质结样品的变频电容 电压 (C V)特性 ,对Al0 2 2 Ga0 78N势垒层表面态的性质进行了研究 .结果发现在小偏压下 ,样品的电容随着测量信号频率的增加而下降 ,说明势垒层中存在表面态 .实验数据分析表明 :表面态密度约为 10 13 cm-2 量级 ,表面态的时间常数比势垒层中其他局域态大 .随着空间隔离层厚度的增加 ,势垒层中其他局域态密度随之增加 .在金属电极和Al0 2 2 Ga0 78N势垒层之间加入Si3 N4绝缘层可以对表面态起到显著的钝化作用 ,使表面态密度降为～ 10 12 cm-2

Characteristic of the surface states of modulation doped Al 0.22 Ga 0.78 N/GaN heterosturctures is investigated by means of frequency dependent capacitance voltage( C V ) technique.It is found that the capacitance decreases with increasing signal frequency under small forward bias voltage.This indicates the presence of the surface states on the surface of the barrier layer.The analysis of experimental data indicates that the density of the surface states is ～10 13 cm -2 ,and the time constant of the surface states is smaller than that of other local states in the barrier layer. When the thickness of the spacer increases,the density of the local states in the Al 0.22 Ga 0.78 N layer increases correspondingly.The presence of the insulating layer between the metal contact and the surface of Al 0.22 Ga 0.78 N can passivate the surface states remarkably,which decrease the density of surface states down to ～10 12 cm -2 .