Tunneling and nonparabolicity effects in in-plane magnetic fields.

Abstract

In this paper, tunneling processes between two two-dimensional electron systems in in-plane magnetic fields are used to investigate the nonparabolicity in the GaAs conduction band. The two two-dimensional systems are realized on a GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As heterostructure and are separated by a barrier of only 200 \AA{}. All resonant tunneling processes between the quantized states on each side of the barrier are reflected as large and narrow peaks in the current-voltage characteristics. If a small magnetic field is applied perpendicular to the direction of the tunneling current, all resonance peaks are significantly broadened and shifted to different bias voltages. In addition, these peaks exhibit a characteristic shoulder, which is not present at zero magnetic fields. The broadening of the resonances is well understood in terms of common models, but to explain the shifting of the peaks and the formation of the characteristic shoulder, different effective masses in the emitter and collector electrode have to be assumed. Comparing the experimental data with the results of a model calculation, the effective mass in the two-dimensional subbands is determined as a function of energy.