Intrinsic admittance of unipolar double-barrier resonant-tunneling structures

Abstract

Following the definition of admittance, we have performed a theoretical analysis of the total intrinsic admittance of unipolar double-barrier resonant-tunneling structures. The theory includes contributions from the tunneling currents through the barriers, as well as from the charge distribution. We have solved the problem numerically for small ac voltage amplitudes in the framework of linear response. The calculations are fully quantum mechanical in the Hartree approximation. In linear response, and at frequencies much smaller than the internal frequencies of the system, the susceptance is found to be entirely of a capacitive nature. We have studied both a symmetric and a highly asymmetric sample, with a thick second barrier at the collector side. For the symmetric sample we found that the susceptance-voltage characteristic depends strongly on both frequency and temperature. A $\ensuremath{\delta}$-shaped peak in the susceptance is found in the negative differential resistance region, where the conductance also depends strongly on frequency. For the asymmetric sample the susceptance exhibits a sharp maximum in the negative differential resistance region, although its value is smaller than that for the symmetric case. The frequency dependence of the susceptance is also found to be quite weak for the asymmetric sample.