Activation of arsenic as an acceptor in Hg_1−xCd_xTe under equilibrium conditions

Abstract

Arsenic is an amphoteric impurity in Hg_1−xCd_xTe. Under tellurium-rich conditions, it tends to occupy metal-sublattice sites and act as a donor; while under mercury-rich conditions, it tends to occupy the tellurium sublattice and act as an acceptor. In this process, mercury from the ambient, first, displaces an arsenic atom (donor) occupying a metal-sublattice site. This arsenic atom, in turn, displaces a tellurium atom, taking residence on the tellurium sublattice (acceptor). A second mercury atom combines with this excess tellurium atom at a surface or other crystalline discontinuity. A quantitative knowledge of the equilibrium reaction is important both to understand point defects and doping in HgCdTe. An investigation of this equilibrium under selected mercury pressures spanning the entire range from the tellurium-saturated phase limit to the mercury-saturated phase limit reveals that a majority of the arsenic remains on the sites in the tellurium sublattice even under tellurium-saturated conditions for arsenic concentrations less than 2×10¹⁶ cm⁻³. With increasing mercury pressure, the relative population of the arsenic atoms on sites in the tellurium sublattice monotonically increases, reaching 100% for the mercury-saturated limit.