LIMITS OF ACCEPTOR IMPURITY DOPING IN WIDE-BAND GAP II-VI SEMICONDUCTORS

The limits of acceptor doping in wide band gap semiconductors are examined by considering the case of nitrogen-doped ZnSe. Starting from experimental observations on defect generation associated with N doping, it is shown how self-compensation due to impurity-defect pairs leads to a saturation of the free carrier concentration, in agreement with published electrical measurements. At high doping level, the statistical fluctuations in local impurity and compensating centre concentrations produce a random distribution of potential wells and hills in the semiconductor. An expression of the effective free carrier concentration above the mobility edge is obtained which predicts a sharp drop of the electrical conductivity with increasing impurity content.