Correlation of arsenic incorporation and its electrical activation in MBE HgCdTe

The behavior of arsenic for p-type doping of MBE HgCdTe layers has been stu died for various annealing temperatures and arsenic doping concentrations. We have demonstrated that arsenic is in-situ incorporated into HgCdTe layer s during MBE growth. The carrier concentration has been measured by the Van der Pauw technique, and the total arsenic concentration has been determine d by secondary ion mass spectroscopy. After annealing at 250 degrees C unde r an Hg over pressure, As-doped HgCdTe layers show highly compensated n-typ e properties and the carrier concentration is approximately constant (simil ar to mid 10(15) cm(-3)) until the total arsenic concentration in the HgCdT e layers approach mid 10(17) cm(-3). The source of n-type behavior does not appear to be associated with arsenic dopants, such as arsenic atoms occupy ing Hg vacancy sites, but rather unidentified structural defects acting as donors. When the total arsenic concentration is above mid 10(17) cm(-3), th e carrier concentration shows a dependence on the arsenic concentration whi le remaining n-type. We conjecture that the increase in n-type behavior may be due to donor arsenic tetramers or donor tetramer clusters. Above a tota l arsenic concentration of 1 similar to 2 x 10(18) cm(-3), after annealing at 300 degrees C, the arsenic acceptor activation ratio rapidly decreases b elow 100% with increasing arsenic concentration and is smaller than that af ter annealing at 450 degrees C. The electrically inactive arsenic is inferr ed to be in the form of neutral arsenic tetramer clusters incorporated duri ng the MBE growth. Annealing at 450 degrees C appears to supply enough ther mal energy to break some of the bonds of neutral arsenic tetramer clusters so that the separated arsenic atoms could occupy Te sites and behave as acc epters. However, the number of arsenic atoms on Te sites is saturated at si milar to 2 x 10(18) cm(-3), possibly due to a limitation of its solid solub ility in HgCdTe.