ac response of bipolar double-barrier resonant-tunneling structures

We have developed an explicit formulation of the total intrinsic admittance of bipolar double-barrier resonant-tunneling structures. The theory includes contributions from the tunneling currents through the barriers and the recombination current, as well as from the charge distribution. We have numerically solved the problem 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 below the internal frequency of the system, the susceptance is found to be entirely of a capacitive nature. We have studied both an ordinary bipolar double-barrier resonant-tunneling structure and an optimized resonant-tunneling light emitting diode. We have investigated the frequency dependence of the admittance as well as the dependence on recombination time. In both samples a delta-shaped peak in the susceptance is found in the negative differential resistance region. However, the details of the frequency response are found to be closely related to the specific structure under consideration. [S0163-1829(98)04739-0].