The resistivity and photoluminescence of Zn(S, Se):I single crystals annealed in liquid Zn at several temperatures have been studied. The change in resistivity with annealing temperature had a characteristic activation energy of 16 kcal/mole and was independent of the S:Se ratio suggesting that Zn is diffusing into the crystal. The photoluminescent spectra was not changed by annealing; however, the room temperature photoluminescence efficiency increased as Zn diffused in and decreased when Zn diffused out. It was concluded that diffused Zn only contributes to the resistivity and the thermal quenching centers. In addition it was found that excess iodine gave an additional yellow luminescent band centered at 2.23 eV (560 nm).The photoluminescence of zinc sulfoselenide crystals, Zn(S,Se):halogen, as a function of ZnSe concentration is of basic interest in understanding II-VI compound semiconductors because ZnSe is isoelectronic with GaAs and Ge. From a practical point of view, the phosphor ZnSe: Cu: Br has been proposed as a possible red color TV phosphor (1) and is an electroluminescent material (2, 3) ; yellow-emitting Zn(S,Se) :Cu:Br has been shown to be a brighter electroluminescent phosphor than ZnS: Mn: Cu and has been used in an EL TV display panel (4).The majority carriers of ZnSe at room temperature are electrons. The resistivity of n-ZnSe as-grown single crystals is high but is lowered by annealing in Zn (5). Cu2Se-ZnSe and Cu2S-ZnS emit a brilliant d-c electroluminescence (6, 7). Stringfellow and Bube have measured the photoluminescence and excitation spectra at 85~ and the thermally stimulated luminescence of n-ZnSe(SA) annealed in Zn (8). They concluded that the fact that the center lies 0.5-0.6 eV above the valence band is an intrinsic defect.In this work the resistivity and photoluminescence of Zn(S,Se):I single crystals before and after annealing in Zn were studied. This report will describe first the effect of annealing on Zn(S,Se) :I crystals as determined by the change in resistivity, thus confirming that Zn diffuses into the crystals. Then the photoluminescence of Zn (S,Se) :I crystals as-grown and annealed will be described.
ExperimentalThe Zn(S, Se):I single crystals were grown by an iodine transport technique (9, 10) from the amorphous powder mixture; the ZnSe powder was a vacuum deposition grade from the Apache Chemical Company and the ZnS powder was a luminescent grade from RCA. The crystals did not grow under conditions of excess Zn but only grew in an excess Se and S. X-ray diffraction analysis indicated that all Zn(S,Se) crystals formed solid solutions over the whole range of composition within 2% error from the expected composition.The crystals, about 5g, were cut into slices along the plane and were polished by carborundum (1/~ grit size) to 0.5 mm thickness. These sliced pieces were used in the study of the photoluminescence and resistivity.The crystals (about 100 rag) were placed in a quartz capsule (1 cm 3) which was evacuated to 5 • 10 -6 Tort by means of an ion pump and were ...