Focus Issue on Modelling of Quantum Mechanical Effects in Nanoscale Devices

Non-monotonic mobility μ of electrons is obtained in a pseudomorphic GaAs/In_xGa_1−xAs high electron mobility transistor having double quantum well structure with asymmetric doping concentrations in the outer barriers. A dip in μ occurs close to the resonance of subband states because of the quantum mechanical transfer of the wave functions between the wells. Near resonance, the asymmetry in subband wave functions and anticrossing of energy levels as a function of doping concentration influence the intra- and intersubband scattering rate matrix elements. Near resonance, the subband wave functions spread asymmetrically and the energy levels exhibit anticrossing as a function of doping concentration thereby influencing the intra and intersubband scattering rate matrix elements. The dip in μ, which amplifies with raise in the asymmetry of the width of wells, is basically due to the subband mobilities limited by the interface roughness scattering. We also show that an appropriate selection of the structure parameters leads to a hump in mobility dominated by the intersubband effects on the screened ionized impurity scattering potential under double subband occupancy. The nonlinearity in μ can be utilized to study the characteristics improvement of devices such as high electron mobility transistors.

In this work, we present theoretically the effect of external electric field F_e on low temperature multisubband electron mobility μ in V-shaped double quantum well (V-DQW) HEMT structure. We consider the impact of ionised impurity and alloy disorder scatterings for the calculation of μ. We show that, in the proposed structure, when F_e, is absent, there are two subbands occupied below the Fermi levels. However, as F_e increases, there is an alteration of the potential profile, which changes the energy levels and wave function distributions leading to variation of occupation of subband states, i.e. from double to single. During double subband occupancy, initially, μ enhances with F_e, attains a peak value and then decreases. Whereas, for F_e where the transition from double to single subband occupancy occurs, there is a sudden rise in μ due to the cease of inter-subband interaction. It is interesting to note that different structure parameters, e.g. well widths Ww, central barrier width B_C, doping concentrations N_D, alloy concentrations x_v at the well edges of the V-DQW have a fascinating impact on μ. We show that increasing Ww, and B_C and decreasing N_D, and x_v enhances μ.

Gate-all-around (GAA) cylindrical Si channel nanowire field-effect transistor (NW-FET) devices have the potential to replace FinFETs in future technology nodes because of their better channel electrostatics control. In this work, 3D TCAD physics-based simulations are performed for the first time to evaluate the potential of NW-FETs at extreme scaling limits of 3 nm using quantum corrected 3D density gradient finite element simulations. Simulations are also performed to study the effects of process-induced variabilities, such as metal grain granularity (MGG) on 3 nm gate length device performance in the sub-threshold region. The importance of MGG induced variability for gate-all-around stacked devices having 3 horizontal nanowires in the 3 nm technology nodes is shown.