Shirun Ho

Three-dimensional numerical analysis of multi-mode quantum transport in zero-dimensional resonant tunnelling diodes

Lateral-mode non-conserving resonant tunnelling through a zero-dimensional AlGaAs/InGaAs/AlGaAs resonant tunnelling diode (0D RTD) has been analysed by numerically solving the three-dimensional Schrodinger equation with scattering boundary conditions. The authors report on the effect of lateral-mode mixing, caused by elastic scattering due to an hour-glass-shaped confinement potential, on the multi-mode transmission properties and current-voltage characteristics of the device. The calculated S-matrix clearly shows both new transmission peaks in the off-diagonal components which measure the lateral-mode-non-conserving resonant tunnelling and the related Fano-resonance-type structures in the diagonal components which represent an interference between the second-order resonant tunnelling process and the conventional tunnelling process for the off-resonant condition. The difference between the energy separations of the lateral modes in the cathode region and in the quantum box leads to observable fine current peaks in the current-voltage characteristics due to the lateral-mode-conserving tunnelling.

Possible new structure for one‐dimensional electron‐gas systems by interface bending of n‐AlGaAs/u‐GaAs heterojunctions

A new concept in one‐dimensional electron‐gas (1DEG) systems is proposed by introducing periodic bending of the heterointerface of an n‐AlGaAs/u‐GaAs modulation‐doped structure. The carrier densities and the electrostatic potential of this system are numerically analyzed based on the classical drift‐diffusion model where the doping concentration ND of n‐AlzG1−zAs is 1.0×1018 cm−3, the aluminum molar fraction z of AlzGa1−zAs is 0.3, the carrier density of p‐type GaAs is 1.0×1014 cm−3, and the bending angle of the heterointerface is 90°. We found that electrons are more accumulated in convex regions of the u‐GaAs layer than in concave ones, and the electron density in a convex region is about twice that in the conventional two‐dimensional electron‐gas structure. We can treat this high density of electrons as a 1DEG channel for field‐electron transistors (FETs) when the period of the bending interface is about 850 A.

Dynamic Simulation Of Multiple Trapping Processes And Anomalous Frequency Dependence In GaAs MESFETs

Frequency dependent characteristics of GaAs MESFETs due to deep traps are one of the most serious problems in achieving high device performance. In this study, mechanisms of frequency dependent transconductance Gm and output resistance Rd are unifyingly revealed by incorporating dynamics of quasi-Fermi levels. Multiple frequency dispersions of Gm and Rd, and pulse narrowing phenomena due to electron and hole traps are demonstrated using hydrodynamic transport theory and a Schokkley-Read-Hall type deep trap model, where rate equations associated with multiple trapping processes are analyzed self-consistently. It is also found that there exist spatial and time effects of multi-traps on the dispersion characteristics.

Theoretical Analysis Of Transconductance Enhancement Due To Electron Concentration Dependent Screening In Heavily Doped Systems

The transport mechanism in heavily doped systems is dominated by ionized impurity scattering involved with electron polarization. The objectives of this paper are to present a new mobility model which incorporates the quantum mechanical screening effect and to introduce a concept of effective mobility to reveal the possibility of transconductance enhancement. It is also demonstrated for the first time that heavily doped and short channel devices actually induce the enhanced characteristics.

Quantum Transport Simulation Based on Wigner Formula

The superiority of nonequilibrium quantum transport simulation based on the Wigner Formula over a conventional Transfer Matrix Method is clarified for the first time. With a new contact model, the present simulation technique is applied to a double barrier Resonant Tunneling Diode and the influence of some perturbations on quantum interference effects is investigated systematical ly. In particular it predicts that both ohmic drop and electronic accumulation in quantum mechanical distribution in a cathode region cause a remarkable decrease in the peak to valley ratio in current voltage characteristics.