Incorporation and Activation of Arsenic Dopant in Single-Crystal CdTe Grown on Si by Molecular Beam Epitaxy

We report the use of molecular beam epitaxy to achieve p-type doping of CdTe grown on Si(211) substrates, by use of an arsenic cracker and post-growth annealing. A high hole density in CdTe is crucial for high efficiency II-VI-based solar cells. We measured the density of As in single-crystal CdTe by secondary ion mass spectroscopy; this showed that high As incorporation is achieved at low growth temperatures. Progressively higher incorporation was observed during low-temperature growth, presumably because of degradation of crystal quality with incorporation of As at such defect sites as dislocations and defect complexes. After As activation annealing under Hg overpressure, hole concentrations were obtained from Hall measurements. The highest doping level was similar to 2.3 x 10(16) cm(-3), and near-10(16) cm(-3) doping was readily reproduced. The activation efficiency was similar to 50%, but further optimization of the growth and annealing conditions is likely to improve this value.