INTRINSIC HIGH-FREQUENCY CHARACTERISTICS OF TUNNELING HETEROSTRUCTUREDEVICES

A general numerical method has been developed to solve the periodic ti me-dependent Schrodinger equation under a. weak ac held where the quan tum transmitting boundary method is employed to formulate boundary con ditions of far-from-equilibrium open systems. Also derived are current components for ac small-signal analysis, We apply the method to a res onant-tunneling diode (RTD) structure. Our calculations illustrate tha t the assumption of Lorentzian-like form of line shapes of the current functions is no longer valid at high frequencies. Thus a careful trea tment to these integral functions is fundamental to obtain a physicall y reasonable result. Results of linear admittance, rectification coeff icient, and second-harmonic generation coefficient are presented as a function of frequency and bias, at both positive-differential resistan ce and negative-differential resistance (NDR) region. The calculations have shown that at high frequencies (several THz), the reactive featu re of RTD, whether inductive or capacitive, depends on the bias and fr equency. The capacitive feature, i.e., the positive imaginary part of the admittance, reaches maximum in the middle of the NDR region. This behavior can be ascribed to the confined electrons in the wed. The cha racteristic of the transition from electron to optical behavior is obs erved when the frequency increases. The rectification coefficient and second-harmonic generation coefficient show a resonant enhancement at high frequencies. A comparison with the results obtained by the Wigner function is demonstrated. Different definitions of the ac reactive cu rrent component are discussed in order to clarify the confusion in the literature.