Precipitation effects in indium-doped zinc selenide

Single crystals of zinc selenide are grown containing indium in concentrations ranging from 5 to 1000 ppm, using a vapour phase technique. Solubility of the indium in the zinc selenide is complete under the growth conditions employed. Examination of chemically thinned samples of such crystals in the transmission electron microscope shows that the only observable crystallographic defects are long thin twins. Similar observations are made with undoped crystals. When samples containing concentrations of indium in excess of 50 ppm are heated in molten zinc at 850 0C, they become darker and more opaque as precipitation effects occur. In addition to long thin twins which are still present, the samples now contain stacking faults and dislocations. All of these defects are usually decorated with precipitates. At low concentrations the precipitates are spherical, but at higher concentrations they begin to assume definite crystallographic shapes with three- and fourfold symmetry depending on the crystallography of the boundary that they decorate and on the orientation of the foil. Random precipitation also occurs. With crystals with the highest indium concentrations, the precipitates may be observed in the optical microscope. They occur as features with much larger dimensions, approximately 50 μm, and consist of short segments which often intersect to produce an overall impression of badly formed rosettes. The nature of the precipitates and the mechanism of their formation are discussed. (author)