INTRINSIC ADMITTANCE OF UNIPOLAR DOUBLE-BARRIER RESONANT-TUNNELING STRUCTURES

Following the definition of admittance, we have performed a theoretica l analysis of the total intrinsic admittance of unipolar double-barrie r resonant-tunneling structures. The theory includes contributions fro m the tunneling currents through the barriers, as well as from the cha rge distribution. We have solved the problem numerically for small ac voltage amplitudes in the framework of linear response. The calculatio ns are fully quantum mechanical in the Hartree approximation. In linea r response, and at frequencies much smaller than the internal frequenc ies of the system, the susceptance is found to be entirely of a capaci tive nature. We have studied both a symmetric and a highly asymmetric sample, with a thick second barrier at the collector side. For the sym metric sample we found that the susceptance-voltage characteristic dep ends strongly on both frequency and temperature. A S-shaped peak in th e susceptance is found in the negative differential resistance region, where the conductance also depends strongly on frequency. For the asy mmetric sample the susceptance exhibits a sharp maximum in the negativ e differential resistance region, although its value is smaller than t hat for the symmetric case. The frequency dependence of the susceptanc e is also found to be quite weak for the asymmetric sample. [S0163-182 9(98)04939-X].