Electron Transport Properties of AlxGa1−xN/GaN Transistors Based on

Abstract

High-electron-mobility transistors (HEMTs) based on Al x Ga 1-x N/GaN heterostructures have great potential for applications in power electronics and radio-frequency (RF) applications. Operating under large bias and electric fields, hot electrons are present in the channel where they can activate pre-existing benign defects that cause scattering or carrier trapping, resulting in device degradation, such as threshold-voltage shifts and transconductance degradation. Here we report a comprehensive investigation of the electron transport properties of wurtzite-phase GaN and AlN and of an Al 0.25 Ga 0.75 N/GaN HEMT by solving the Boltzmann transport equation with a synchronous ensemble Monte Carlo technique and employing first-principles electronic properties, including the full energy bands, phonon dispersions, and electron-phonon scattering rates. We find that, for electron collisions with the highest-energy optical phonon mode, nonpolar scattering by optical phonons contributes comparable to polar scattering. Polar scattering with acoustic phonons, i.e., piezoelectric scattering, is found to be as important as the polar scattering with optical phonons for low energy electrons at room temperature. We compare the calculated high-field transport characteristics of bulk GaN with previously reported results. We also calculate the nonpolar acoustic deformation potential, nonpolar optical deformation potential, and high-field transport characteristics of bulk AlN. We find that inclusion of piezoelectric scattering results in a low-field electron mobility of ~450 cm 2 /(V·s), which is very close to the experimental value. Simulation results are presented for an Al 0.25 Ga 0.75 N/GaN HEMT, including electric field, average carrier kinetic energy, and drift velocity in the channel. Finally, we present the carrier energy distribution function in the conducting channel, which is key to accurately determine hot-carrier-caused device degradation, and identify possible routes to an improved device design.

Increasing the mobility and power-electronics figure of merit of AlGaN with atomically thin AlN/GaN digital-alloy superlattices

“…We also use the electron-phonon matrix elements calculated using density-functional perturbation theory at the LDA level, which is a valid approximation since LDA wave functions are nearly identical to G0W0 wave functions in common semiconductors [34], and therefore should give accurate electron-phonon matrix elements. Our mobility results agree with Monte-Carlo simulations [41] and experimental measurements [42] of the mobility of AlN to within 25%, which is typical for first-principles calculations [43]. The effective mass, frequency of the highest LO mode, and dielectric constants of the 1ML superlattice are close to linear interpolations of the end binary compounds.…”

Understanding high-field electron transport properties and strain effects of monolayer transition metal dichalcogenides

“…The full-band full-scattering approach is thus more accurate than the conventional MC approaches that assume analytical expressions for transition rates and/or band structure. [30] The full-band full-scattering approach has been applied to study MX2, [12] and other 2D materials such as silicene, [17] germanene [17] and InSe. [18] Compared with those cases, here we use a much finer grid, which is necessary to converge the results [25] (see Fig.…”

“…The MC method is a statistical method used to yield numerical solution to the Boltzmann transport equation (BTE) [26][27][28][29][30][31][32] which includes complex band structure and scattering processes. In contrast to low-field case where analytic solutions can be derived under certain approximations, in high field, the numerical method becomes necessary due to the nonlinear terms in BTE.…”

An innovative technique for electronic transport model of group-III nitrides

“…However, the computational tool based on DFT suffers with limitations that it can be used for a very small structure of clusters of atoms. The other big limitations of DFT are that many times it doesn't correctly treat the exchange interaction and long-range non-covalent interactions 4 – 8 . Semi-empirical methods appear to be most suitable technique to address these issues.…”

“…Semi-empirical methods appear to be most suitable technique to address these issues. Furthermore, it can be easily extended to simulate dynamical properties of the materials 4 – 11 .…”