The electrical and optical properties of zinc selenide

Abstract

Zinc selenide is a II - VI compound semiconductor with a vide band gap of 2.67 eV at room temperature, and is therefore capable of emitting visible luminescence. The main purpose of the research reported in this thesis was to study zinc selenide crystals grown in the department with the aim of developing a suitable material for the manufacture of red- emitting electroluminescent diodes. It is hoped that these will eventually be cheaper and easier to produce than gallium arsenide-phosphide devices. The most satisfactory means of reducing the resistivity of zinc selenide to values consistent with its use as a device (approx. 1 ohm cm.) was to heat nominally undoped crystals In molten zinc. Measurements of the Hall voltage and conductivity over the range 15ºK to 400ºK revealed a shallow donor level (Ed = 0.012 eV) thought to be associated with unremoved trace impurities of chlorine. Manganese was Introduced into several crystals to provide an efficient luminescent centre. The characteristic manganese emission band at 85ºK was found to lie at 5870 Å with a half width of 0.13 eV. Under 3650 Å excitation, however, the manganese emission was swamped by a band at 6400 Å attributed to copper contamination, and a broad band at 6150 Å which appeared to be the self-activated emission of zinc selenide. The manganese emission could be isolated when crystals were excited in one of the two characteristic excitation bands (5040 Å and 5370 Å). A smaller excitation band was also observed at 4660 Å, All samples, Including those containing manganese, heated in zinc to reduce their resistivity, were found to emit the self-activated band only, thought to be the result of chlorine impurity. An Anger process was assumed to account for the disappearance in semiconducting samples of the manganese emission under photo excitation and yet explain its appearance in the emission from electroluminescent diodes containing manganese.