Activation of Arsenic in Epitaxial Hg_(1-x)Cd_(x)Te (MCT)

摘要

This paper reviews arsenic (As) dopant activation processes in the various forms of epitaxial MCT. Extrinsic doping of MCT is an important part of MCT technology and As doping is preferred as it is a shallow acceptor dopant with low diffusivity and 100percent activation can be achieved under the correct growth and/or post-growth annealing conditions. It is, however, amphoteric so that under Te-rich growth conditions it can be incorporated as a donor (As_(Hg)) and under metalrich conditions as an acceptor (As'_(Te)). For As concentrations up to approx2 X 10~(18) cm~(-3) the amphoteric model provides a satisfactory basis for explaining the behavior on annealing layers at temperatures above approx250 deg C. Under Te-rich conditions in LPE- and MBE-grown layers can be either compensated n-type or the As can be inactive. The quantitative model of Schaake is used to obtain an expression for the activation anneal time in terms of As concentration, layer thickness, composition and temperature. Layers grown by MOVPE can show up to 100percent acceptor activation if the stoichiometric conditions during the CdTe growth cycle of the interdiffused multilayer (IMP) process are maintained as metal-rich. In as-grown MBE layers the evidence indicates that As is incorporated in the form of tetramers that can dissociate at higher temperatures. The issue of establishing whether layers are electrically intrinsic at the annealing temperatures used to activate the As acceptor in LPE and MBE layers is also discussed.