An explicit approximation for surface potential as a function of terminal voltages is developed for partially depleted polysilicon thin-film transistors. The resulting model has taken both Gaussian deep states and exponential tail states into account, which provides a complete modeling for surface potential. Furthermore, a drain current model based on terms of surface potential is proposed. Surface potential and drain current calculations are successfully verified by comparisons with numerical and experimental ones.

The hole mobility enhancement mechanism of wurtzite (0001)-oriented gallium nitride (GaN)/AlN heterojunction quantum well (QW) under stress engineering is investigated to overcome the low hole mobility, which is considered to be the fundamental obstacle toward the realization of GaN-based complementary electronics. The hole mobility model is obtained by the six-band stress-dependent $\textit{k}$ $\times$ $\textit{p}$ Hamiltonian and the Kubo–Greenwood formula, taking the scattering rates of acoustic phonon, polar optical phonon, and surface roughness into account. Using these methods, the microscopic relationship between stress and hole mobility can be predicted according to the variation of 2-D valence subband dispersion. We demonstrate that the biaxial tensile stress is not a desirable way in the hole mobility enhancement because a large compressive strain induced by the pseudomorphic GaN/AlN heterointerface has to be overcome. We also find that due to the efficient achievements in both effective mass reduction and hole scattering suppression, the uniaxial compressive stress along the current channel and the uniaxial tensile stress perpendicular to the current channel can increase the hole mobility significantly. Under the combined effect of these two 8 GPa non-exclusive mechanisms, a sevenfold mobility enhancement can be obtained, up to the theoretical value of 190 cm $^{\text{2}}$ /Vs at room temperature.

A quantized valence subband model is proposed to study the energy dispersion of zinc-blende GaN P -channel heterojunction quantum well under arbitrary stress. Anisotropic band structures of bulk GaN and GaN in quantum well under field confinement effect are computed using a six-band stress-dependent k·p Hamiltonian and self-consistently Poisson–Schrödinger equation. A comprehensive study of microscopic relationship between stress and hole effective mass in GaN quantum well has been performed according to the stress effects on quantized valence subband. Simulation results show that uniaxial compression can be considered as the most effective stress in the hole effective mass reduction of zinc-blende GaN heterojunction.

The influence of uniaxial compressive stress with different orientations to the current channel on the physical and transport properties of the wurtzite GaN heterojunction quantum well is investigated in this work. By using the six-band stress-dependent k × p Hamiltonian, accurate two-dimensional physical pictures are given for the quantized valence subband under the uniaxial compressive stress on the (0001) transport plane. The low-field hole mobility is obtained by the Kubo–Greenwood formula, taking the scattering rates for acoustic phonon, polar optical phonon, and surface roughness into account. Using these methods, the microscopic relationship between the orientation of uniaxial compressive stress and low-field hole mobility is obtained according to the variations of valence subband dispersion and hole effective mass. Results show that for temperatures around and above room temperature, the acoustic phonon scattering is predominant. We find that the mobility gain is mostly contributed from effective mass, and there is an increasing trend under uniaxial compressive stress with all orientations due to the effective mass reduction. For the same stress value, the mobility decreases monotonically as the stress orientation changes from 0° to 90° with respect to the current channel. At room temperature, the calculated low-field hole mobility is 182 cm²/V s under 8 GPa uniaxial compressive stress parallel to the current channel, with the hole density of 5.5 × 10¹³ cm⁻² and the effective electric field of 0.93 MV/cm.