A study of the growth of monocrystals of tellurium and selenium-tellurium alloys by the Czochralski method has been made, together with measurements of the photoconductivity in such materials. In tellurium, it was found that large temperature gradients occur within a growing ingot which cause an increase in the concentration of lattice defects. This concentration can be reduced by subsequent annealing. An etch pit orientation effect was observed enabling the growth direction of an ingot to be determined, arising from a correspondence between preferential growth and etching planes. Photoconductivity in tellurium at 77 K was found to be decreased by abrasive polishing of the samples and increased by annealing. Transient photoconductivity was found to be characterized approximately by two time constants, one of the order of microseconds and the other tens of microseconds. The largest D* detectivity measured on the samples was 1.3 x 10('11) cm Hz(' 1/2)w('-1) at 3.5 (mu)m. Crystals of Se(,x)Te(,1-x) were prepared by the Czochralski method for Te-rich and Se-rich compositions with 0.1 > x > 0.95. For intermediate compositions with 0.1 < x < 0.95 it was not possible to obtain Czochralski-ingots due to a meniscus rupture problem arising from excess selenium at the growing interface. In this case crystallographically aligned samples were obtained by a slow cooling method. Measurements on the Se(,x)Te(,1-x) alloys showed a continuous wavelength displacement of the photoconductivity maximum from 3.7 to about 0.8 (mu)m in going from tellurium to selenium. This was accompanied by an increase of some 5 orders of magnitude in the photoresponse, in the photoconductive decay time constants and in the electrical resistivity. From the results the estimated energy gaps were found to change continuously from tellurium to selenium with a possible change of slope starting near 40 at.% Se.

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