Electron spin resonance in zinc selenide

Abstract

Electron spin resonance techniques were applied to study crystals of ZnSe both doped and undoped. Crystals grown by sublimation at 1300ºC were found to have a mixed cubic-hexagonal structure. Annealing these crystals at 1050ºC increased the hexagonal component. This is the opposite of what is usually observed in crystals produced by the flow process. ZnSe crystals produced at 850ºC by the iodine transport method were found to have a cubic structure. No cubic → hexagonal phase transition could be achieved in these crystals. From the experimental data it is concluded that the hexagonal phase in crystals grown at 1300ºC occurred as a result of the presence of an impurity, probably oxygen. Electron spin resonance of Mn was studied in detail in cubic, in twinned and in cubic-hexagonal ZnSe crystals. Comparing the Mn concentration and distribution in crystals produced at 1300ºC and at 850ºC, it was found that the solubility of Mn was larger in crystals grown at 1300ºC. Attempts were made to dope ZnSe with Mn by diffusion, but results indicated that Mn does not diffuse into ZnSe. However, spin resonance results showed that annealing ZnSe: Mn crystals in molten Zn at 850ºC removes some of the Mn impurity. Electron spin resonance investigations were also carried out in ZnSe crystals doped with I, CI, Al, and In. In these crystals spin resonance signals characteristic of mobile donor electron were detected. These signals were all found to be affected by annealing in molten Zn, and furthermore they were all photosensitive. Addition of 0.01% Cr to ZnSe was found to prevent charge transport. Spin resonance of a sintered sample containing Cr indicated a trapping level associated with Cr at 0.51 eV below the conduction band.