Magnetotunneling and Magnetic Freezeout in n-GaAs-Undoped AlxGa1-xAs-n+GaAs Capacitors

Abstract

We have reported the observation of a remarkable periodic structure in the current-voltage (I-V) curves of n-GaAs-Undoped AlxGa1-xAs-n+GaAs capacitors at 1.6 K in the presence of high magnetic fields.(1) Current flow in the semiconductor-insulator-semiconductor (SIS) capacitor is due to direct electron tunneling from n-GaAs through AlxGa1-xAs into n-GaAs. The periodic structure is seen only for magnetic fields, B, high enough (B>4 T) that magnetic freezeout of carriers in the n-GaAs-occurs. Contrary to the usual observations of magnetocon- duction or magnetophonon effects in semiconductors, neither the voltage spacing nor the phase of the observed oscillations depends on the magnitude of the magnetic field. The voltage periodicity is 0.036 V, independent of orientation of magnetic field. Results were presented for samples oriented perpendicular to the direction of the magnetic field; sixteen periods are observed in this case. We present here results for a sample oriented parallel to the magnetic field; at least thirty periods can be observed for −1.2 V<VG<0 V where VG is the voltage applied to the n+GaAs gate. Periodic structure is also seen in capacitance-voltage (C-V) characteristics of SIS capacitors. The mechanism appears to involve sequential LO phonon emission events by ballistic electrons. To our knowledge this is the first example of sequential single-phonon emission observed in electron transport.