Study of Wannier-Stark Effect in GaAs/AlGaAs Superlattices

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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.