The estimation of impact ionization coefficients for $\beta $-Ga$_{2}$O$_{3}$

TL;DR

This paper estimates impact ionization coefficients for anisotropic $eta$-Ga$_{2}$O$_{3}$ along different crystallographic directions, fitting models to universal plots, and compares results with other wide-bandgap semiconductors.

Contribution

It provides the first estimation of impact ionization coefficients for $eta$-Ga$_{2}$O$_{3}$ along multiple directions using model fitting and compares these with other semiconductors.

Findings

Maximum ionization rate of 3.98×10^6 cm^{-1} along [010] direction.

Estimated critical electric field of 0.921×10^8 V/cm along [010].

Phonon mean free path varies with direction, affecting thermal properties.

Abstract

Impact ionization coefficients of anisotropic monoclinic $\beta $-Ga$_{2}$O$_{3}$ are estimated along four crystallographic directions and the plot for the $\left[ 010 \right]$ direction is shown. The approximation models were fitted to Baraff's universal plot for ionization rate in semiconductors and the values were obtained for $\beta $-Ga$_{2}$O$_{3}$. The phonon mean free path of $\beta $-Ga$_{2}$O$_{3}$ was estimated to be 5.2604 \si{\angstrom} using Gray medium approximation. The phonon group velocity takes the value of longitudinal acoustic phonons. The ionization rate has a maximum value of $ 3.98\times \,10^{6}\,cm^{-1}$ along the $\left[ 010 \right]$ direction over the applied electric field range $(1.43-4)\times10^{7}\,V\,\cdot\,cm^{-1}$. Contrary to expectations, the phonon mean free path along direction $\left[ \bar{2}01 \right]$ is the lowest since it has a lower thermal conductivity to phonon group velocity ratio. The plots were compared with GaN and 4H-SiC, which shows that as bandgap increases the field required for ionization increases. The critical electric field was estimated to be $ 0.921 \times10^{8}\,V\cdot\,cm^{-1}$ along $\left[010 \right]$ direction.