Monte carlo simulations of carrier transport in diamond and GaN thin films: The effect of dislocations and electron interactions

Abstract

Using a molecular dynamics simulation with a Monte Carlo algorithm, we examine the role of dislocations and collective excitations in transport of charge carriers in the conduction band of diamond and GaN. For very thin films (LsO.01 pm) and for low fields (F<lO V/p), the energy spectra of both diamond and GUN contain a series of peaks which are attributed to the absorption and emission of discrete plasmons. For thicker diamond films (L=O.l p), there is hot electron transport for F-IO V/w and quasi-ballistic transport for F-100 V/,m. In GaN with L=O.Ol pm and fields F-IO V/,, there is a discrete series of peaks in the energy spectrum corresponding to excitations of polar optical phonons. The inclusion of extended defects in the form of line dislocations with densities up to 1011 cm-2 shows the expected broadening of the distribution but does not suppress the quasi-ballistic transport characteristics. I. Introduction A multi-step model previously used to describe field emission from a thin film metal diamond composite cold cathode can be used to describe the field emission process in other similar wideband gap semiconductor devices involving nitride III-V compounds. The model features internal field emission at the substrate interface for the injection of electrons into the conduction band of diamond, transport through the film and subsequent emission into vacuum[l,2]. In this paper we investigate some new features of the charge transport in the conduction band in diamond and GaN. Earlier calculations by the authors have demonstrated that both quasi-ballistic transport and hot electron transport through diamond and GaN films are possible[3]. However, the collective electron-plasmon interaction (e-pl), the polar-optical interaction and the effects of extended defects such as line dislocations were not included. In this aper, we focus on the influence of these additional scattering processes on the scattering statistics and the energy distribution. The functional form of the first two different types of scattering processes is very similar despite their different physical origin[4]. Both are present in GaN: the electron-plasmon interaction due to the relatively high level of unintentional n-doping (lo17 cm-9, and the polar optical scattering due to the structure of GaN as a 111-V compound. In the calculations to be described, both GaN and diamond will, to facilitate comparison, always have the same electron density in the simulation studies. Our ability to correlate the calculated energy spectra with corresponding scattering statistics provides important insights on the ability of the quasi-classical Monte Carlo algorithm to model electron energy losses due to collective excitations. The fact that ballistic or hot-electron transport may be possible is a consequence of the following physical considerations. The emission rates for the collective