Study of Wannier-Stark Effect in GaAs/AlGaAs Superlattices

为了阐明Di Carlo等人提出的“Wannier-Stark共振”现象，测量了本征层为（GaAs）_5/（AlAs）_2超晶格的PIN二极管的齐纳电流。我们使用的样品是由慕尼黑理工学院的Weimann教授小组种植的。我们采用标准的锁定技术测量了齐纳电流的导数信号，并观察到齐纳电流的二阶导数中的几个峰。峰位与理论值吻合良好。电反射测量也进行了，以澄清电子能带结构的超晶格。所观察到的电反射光谱清楚地表明，斯塔克阶梯的形成在超晶格。斯塔克阶梯的能量与齐纳电流的二阶导数的峰值电压具有良好的对应关系。这些结果有力地说明了Zener电流的二阶导数峰来自于超晶格中的斯塔克阶梯，从而为Wannier-Stark共振提供了实验依据。

In order to clarify the existense of a new phenomenon called "Wannier-Stark resonance" which was predicted by Di Carlo et al., we measured Zener current throught a pin diode with a (GaAs) _5/ (AlAs) _2 superlattice in the intrinsic layr. The sample we used were grown by the group of professor Weimann in Munchen Institute of Technology. We measured the derivative signals of Zener current by employing a standard lock-in technique and observed several peaks in the second derivative of Zener current. The peak positions agree well with theoretical values. Electroreflectance measurements were also carried out so as to clarify electronic band structure of the superlattice. Observed electroreflectance spectra clearly show the formation of Stark-ladders in the superlattice. Energies of the Stark-ladders show good correspondence to the peak voltages of the second derivative of the Zener current. These results strongly indicates that the peaks in the second derivative of Zener current arise from Stark-ladders in the superlattice.In conclusion, we found an experimental evidence for the Wannier-Stark resonances.