E. Bellotti et al., MONTE-CARLO STUDY OF ELECTRON INITIATED IMPACT IONIZATION IN BULK ZINCBLENDE AND WURTZITE PHASE ZNS, Journal of applied physics, 83(9), 1998, pp. 4765-4772
This paper presents a theoretical study of the high field electronic t
ransport properties of the cubic and hexagonal phases of zinc sulfide
(ZnS) using an ensemble Monte Carlo method. Essential features of the
model are the inclusion of realistic energy band structures calculated
from a local pseudopotential method and numerically calculated impact
ionization transition rates. The polar optical phonon scattering rate
has also been computed numerically from the band structure. The relev
ant transport quantities have been computed for field values between 1
00 kV/cm and 2 MV/cm. On the basis of these calculations it is predict
ed that the electron distribution is cooler and the average energy low
er in the wurtzite phase than in the zincblende phase over the entire
field range examined. The difference in average energy between the two
phases becomes pronounced for field magnitudes above 1 MV/cm while it
is smaller in the field range between 700 kV/cm and 1 MV/cm. As a res
ult, the ionization coefficients are expected to be higher in the zinc
blende phase than in the wurtzite phase. This can be attributed to dif
ferences in the density of states between the two polytypes. The quant
um yield has also been computed. It is found that even though the thre
shold for impact ionization is relatively hard in both polytypes, the
threshold for the wurtzite phase is harder than the threshold for the
zincblende phase. (C) 1998 American Institute of Physics.