The Luminescence Characteristics of Some Group III-VI Compounds

The luminescence characteristics of some members of a new class of phosphors, the group III-VI compounds, are described and in particular the results for GaS, GaSe, Ga 2 S 3 , Ga 2 Se 3 and In 2 S 3 are presented. Luminescence bands are studied in self-activated crystals prepared under oxidizing conditions. At low temperatures (60 °K) bands are observed in GaS at 0.66 μm and 0 75 μm, in GaSe at 0.71 μm, in Ga 2 Se 3 at 0.9 μm and in Ga 2 S 3 at 0 425 μm, 0.62 μm, 0 72 μm and 0 87 μm. The analysis of thermoluminescence in Ga 2 S 3 is seen, as in the case of In 2 S 3 , to indicate the existence of carrier trapping states with the abnormally high capture cross section of about 10 -12 cm 2 . Independent studies of the temperature dependence of phosphorescence in In 2 S 3 give the same result. Together with the recent structural analysis of In 2 S 3 and Ga 2 S 3 , these results suggest that the trapping states may be a characteristic of the defect semiconductor lattice. The role of impurities in the formation of an impurity band in other semiconductors is seen in the case of some defect semiconductors to be assumed by the ordered array of lattice defects (vacancies). Although at low temperatures the `defect band' is unoccupied in the unexcited crystal, a contribution to the conductivity following excitation at low temperatures is observed which is not accompanied by luminescence, and is suggestive of carrier motion in such a band.