Abstract
The semiclassical (local) approximation of mass discontinuity in the Wigner theory, when applied to resonant-tunneling diodes (RTD) with wide or high barriers, is shown to lead to unphysical results such as negative valley currents and negative peak-to-valley ratios (PVR). To deal with such problems, we propose to include the full nonlocal effect of mass discontinuity and restore the positive definiteness of the diagonal part of the density matrix. We have studied several examples and established the following points: (i) in the low narrow-barrier case, we obtain substantially lower PVR than that with the local approximation; (ii) in the wide- and/or high-barrier case, we obtain positive valley currents and hence meaningful PVR, indicating the applicability of the present theory to a wide range of RTD; specifically those which are actually in use; (iii) the peak currents are reduced substantially compared to that in the local approximation. In addition, effects of the mass discontinuity on ac characteristics of resonant-tunneling diodes are also presented for the ac admittance and the second-harmonic coefficients. © 1994 The American Physical Society.