Abstract
The purpose of this study has been to investigate the possibilities of doping cadmium telluride CdTe by the technique of ion implantation. Crystals grown by different techniques have been implanted with hydrogen, argon, indium, tellurium and bismuth ions at energies which produce lattice disorder to a mean depth of about 300 A. Electrical activity generated in implanted layers has been studied as a function of ion type, dose, implantation temperature and annealing temperature. The lattice disorder in these layers has also been investigated as a function of implanted ion energy, and dose rate. Measurements using the thermal probe, sheet resistivity and Hall effect techniques have been taken to assess material suitable for implantation and to investigate electrical activity in implanted layers. Damage centres in the CdTe bandgap have been investigated as a function of ion type and annealing temperature, using the Thermostimulated current technique. The Rutherford Backscattering and channelling of alpha particles has been applied to all implanted material to yield information about the amount and distribution of lattice disorder. The technique also gave information on the position of implanted bismuth in the CdTe lattice. Lattice disorder, produced by the above heavy .ions, exhibited annealing characteristics which were dependent on dose and implant conditions. Complete reordering of the lattice was not detected, due to surface evaporation above 450°C. Bismuth ion movement was detected but no substitutional component was observed. On annealing above 450°C implanted bismuth was rapidly lost from the surface. Besides the generation of radiation induced trapping levels, no electrical activity was detected in samples implanted at room temperature. Implanting indium into substrates held at 200°C produced a dose dependent activity and in the best case one in three of the implanted indium ions became electrically active.