Monte Carlo calculation of electron initiated impact ionization in bulk zinc-blende and wurtzite GaN

Abstract

Calculations of the high-field electronic transport properties of bulk zinc-blende and wurtzite phase gallium nitride are presented focusing particularly on the electron initiated impact ionization rate. The calculations are performed using ensemble Monte Carlo simulations, which include the full details of the band structure derived from an empirical pseudopotential method. The model also includes the numerically generated electron impact ionization transition rate, calculated based on the pseudopotential band structures for both crystallographic phases. The electron initiated impact ionization coefficients are calculated as a function of the applied electric field. The electron distribution is found to be cooler and the ionization coefficients are calculated to be lower in the wurtzite phase as compared to zinc-blende gallium nitride at compatable electric-field strengths. The higher electron energies and the resulting larger impact ionization coefficients in zinc-blende gallium nitride are believed to result from the combined effects of a lower density of states and phonon scattering rate for energies near and below 3 eV above the conduction-band minimum, and a somewhat higher ionization transition rate compared to the wurtzite phase. The nature of the impact ionization threshold in both phases of gallium nitride is predicted to be soft. Although there is considerable uncertainty in the knowledge of the scattering rates and the band structure at high energies which lead to uncertainty in the Monte Carlo calculations, the results presented provide a first estimate of what the electron initiated impact ionization rate in GaN can be expected to be.

Very high voltage operation (>330 V) with high current gain of AlGaN/GaN HBTs

“…Assuming the effective collector thickness to be 2 m, the peak electric field at the base-collector junction is calculated to be 1.8 10 V cm, using a breakdown voltage of 340 V and a base doping concentration of 2 10 cm . Considering that surface effects and the presence of electric field crowding at the mesa edge have been neglected, the calculated field is in reasonable agreement with the theoretical predicted breakdown field [9]. The common emitter current-voltage ( -) characteristics and Gummel plot measurements were taken on HP 4145B semiconductor parameter analyzer.…”

High-Temperature Electronics in Europe

“…The transport properties of GaN, A1N, and InN have been studied using analytical calculations and Monte Carlo simulations (see, for example, Littlejohn, et al 1976;Joshi & Raha 1994;O'Leary, et al in pub;Kolnik, et al 1997;Foutz, et al 1997). These properties depend on materials quality, and the values given in Table 1 represent typical or theoretically predicted values.…”

Theory of high field transport and impact ionization in III-Nitride semiconductors

“…With the availability of more reliable information on multiplication gain of front-and backilluminated APD structures, it is also possible to reassess the theoretical understanding and the numerical modeling approach of high field carrier transport in wurtzite GaN and its ternary alloys. In previous investigations [10], [11] of high field carrier transport and impact ionization in wurtzite III-Nitrides a significant number of assumptions, especially about the fitting parameters concerning the carrier phonon interaction, were made. This makes the current models largely untested and the development of a more rigorous model for the carrierphonon interaction is needed.…”