Impact ionization in β-Ga2O3

Abstract

A theoretical investigation of extremely high field transport in an emerging wide-bandgap material β-Ga2O3 is reported from first principles. The signature high-field effect explored here is impact ionization. Interaction between a valence-band electron and an excited electron is computed from the matrix elements of a screened Coulomb operator. Maximally localized Wannier functions (MLWF) are utilized in computing the impact ionization rates. A full-band Monte Carlo (FBMC) simulation is carried out incorporating the impact ionization rates, and electron-phonon scattering rates. This work brings out valuable insights on the impact ionization coefficient (IIC) of electrons in β-Ga2O3. The isolation of the Γ point conduction band minimum by a significantly high energy from other satellite band pockets play a vital role in determining ionization co-efficients. IICs are calculated for electric fields ranging up to 8 MV/cm for different crystal directions. A Chynoweth fitting of the computed IICs is done to calibrate ionization models in device simulators.Recent advancement in electronic structure and lattice dynamics calculations motivates accurate model development for non-equilibrium carrier dynamics. There have been several reports on firstprinciples EPI calculation and subsequent carrier relaxation time estimation with high accuracy [24][25][26] . There are reports on the high-field transport based on empirical pseudo-potential models under rigid-ion approximations [27] that include impact ionization. Conventionally, deformation potential based theories for EPI and a Keldysh empirical ionization model are common practice [28,29] in Monte Carlo simulations. Here, the authors explore impact ionization starting from density functional theory (DFT) under local density approximation (LDA). The uniqueness of this work is that the authors utilize maximally localized Wannier functions (MLWFs) to calculate electron-electron interactions (EEI). While MLWFs have been used in EPI formulation with high accuracy [30], they have not been used to calculate EEI to the best of the

Ultra-high critical electric field of 13.2 MV/cm for Zn-doped p-type β-Ga2O3

“…To the best of the authors knowledge, in the case of β-Ga2O3, the popular value of 8 MV/cm (a value frequently given in the literature) was originally simply from an interpolation (it was indeed not calculated or measured experimentally) on the basis of a band gap energy model reported in 2012 [5]. Short after, further efforts in the theoretical front, corroborated a theoretically calculated critical electric field of 8 MV/cm (for undoped β-Ga2O3) [6]. Irudayadass and Shi [4], predicted a much larger electric field in the range of 9-17 MV/cm but it is largely anisotropic; i.e.…”

Field-plate engineering for high breakdown voltage β-Ga2O3 nanolayer field-effect transistors

“…The impact ionization coefficients of b-Ga 2 O 3 were estimated to be approximately 6.1 Â 10 4 cm À1 and 9.5 Â 10 3 cm À1 at the peak electric elds of 11.4 MV cm À1 (without eld-modulating plate) and 6.6 MV cm À1 (with eld-modulating plate), which are much lower than those of 4H-SiC (1.7 Â 10 6 ) and GaN (1.8 Â 10 4 ) at electric elds of 6.6 MV cm À1 . 38 The b-Ga 2 O 3 shows a lower impact ionization coefficient under the same electric eld due to its high bond strength of the binding energy of Ga-O ($531 eV (O1s)), much larger than that of Ga-N ($397 eV (N1s)) and Si-C ($283 eV (C1s)). The breakdown eld is generally proportional to (energy bandgap) 2-2.5 .…”

Simulation of β - Ga2O3 based MOSFETs for Depletion and Enhancement Mode Operation

“…(1) Where, a= 7.9 × 10 5 /cm and b= 2.92 × 10 7 V/cm [16]. These exact values are considered in the simulations without any modifications.…”