Cl. Fernando et Wr. Frensley, INTRINSIC HIGH-FREQUENCY CHARACTERISTICS OF TUNNELING HETEROSTRUCTUREDEVICES, Physical review. B, Condensed matter, 52(7), 1995, pp. 5092-5104
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functions is no longer valid at high frequencies.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.