Growth of High Quality Lwir Films by Liquid Phase Epitaxy

ABSTRACTGrowth of long wavelength infra-red mercury cadmium telluride films by liquid phase epitaxy has usually yielded films of inferior electrical properties as evidenced by Hall mobilities lower than theoretical values by factors of 5 or more at 77°K. In addition the Hall behavior over the entire temperature range did not follow classical patterns. A systematic series of investigations was conducted to improve the electrical performance of these films by four methods: i) growth of HgCdZnTe films, where a portion of the cadmium was replaced by zinc, ii) growth at temperatures > 550°C, iii) growth at a slow rate on a CdZnTe substrate following ‘Cleaning’ in the melt of the substrate surface and iv) doping the film by controlled levels of indium. The first method did not lead to any improvements in the Hall behavior. In addition, the films grown displayed varying dislocation densities. The second method led to a small but definite increase in the yield of non-anomalous or classical films (5%). The third method yielded films with classical or non-anomalous Hall behavior about 20% of the time. The last method consistently led to films with classical Hall behavior. This was accomplished with indium doping levels at 1.5× 1014/cm3. Preliminary data indicate that it will be possible to go to still lower doping levels while maintaining classical Hall behavior. The improvement in electrical properties of these epifilms can be attributed to the reduction or elimination of type inhomogeneities known to degrade Hall mobilities in films grown by liquid phase epitaxy.