Partial pressure monitoring in cadmium telluride vapour growth

A simple system, based on optical absorption, which allows the partial pressures of cadmium and tellurium vapour over CdTe to be monitored under typical vapour-growth conditions is described. Use of the 326, 479 and 508 nm lines of a cadmium spectral lamp allows the narrow 326nm elemental absorption of cadmium together with the broad (350-600 nm) absorption of the tellurium dimer to be easily monitored with silicon photodiodes and optical bandpass filters. As the two absorptions do not overlap significantly their optical densities may be determined and related to the concentration and hence partial pressures of cadmium and tellurium. The present apparatus has been calibrated for cadmium pressures over the range 1.4-95.2 mbar and for tellurium pressures from 0.2 to 80.3 mbar.