  CdTe can be made semi-insulating by shallow donor doping. This is routinely
done to obtain high resistivity in CdTe-based radiation detectors. However, it
is widely believed that the high resistivity in CdTe is due to the Fermi level
pinning by native deep donors. The model based on shallow donor compensation of
native acceptors was dismissed based on the assumption that it is practically
impossible to control the shallow donor doping level so precisely that the free
carrier density can be brought below the desired value suitable for radiation
detection applications. In this paper, we present our calculations on carrier
statistics and energetics of shallow donors and native defects in CdTe. Our
results show that the shallow donor can be used to reliably obtain high
resistivity in CdTe. Since radiation detection applications require both high
resistivity and good carrier transport, one should generally use shallow donors
and shallow acceptors for carrier compensation and avoid deep centers that are
effective carrier traps.
