Electrical and optical properties of ZnSß{219}xTex-based thin film structures / by Vincent W.S. Chen

Abstract

In this work, a number of electrical and optical properties of MBE-grown ZnS1-xTex thin films we re studied. In carrying out photo conductance measurements, a ZnS.92Te08 - based metal-semiconductor-metal devices were used to test the photo response of this alloy. It was found that the photocurrent obtained in this structure was dominant by the band-edge absorption of ZnS.92Te.08 alloy. A method using ITO (indium tin oxide) as intermediate medium was introduced to bond gold wire to ZnSl-xTex. The results suggest that ZnS1-xTex alloy is potentially capable as tunable UV detector material. The effects of the insulating layer between the Au contact and the ZnS1-xTex surface on the light emitting efficiency of the ZnS1-xTex - based MIS EL cells were examined. Under forward bias, most of the applied voltage was dropped across the insulating layer (I-layer) rather than the depletion region. This voltage drop across the I-layer raised the semiconductor valence band edge. Correspondingly, the hole injection efficiency increased when the top of the valence band approached the metal Fermi level. Under reverse bias, electrons were accelerated in the I-layer. Since the I-layer is thin enough, most the accelerated electrons can pass through the I-layer with high kinetic energy. Their impact-ionizing power was much enhanced after leaving the I-layer and it leads to a significant improvement in the light emitting efficiency compared to structure without the presence of an I-layer. We for the first time found the trace of the existence of DX centers in Al-doped ZnS1-xTex. Using DLTFS technique, we found that there were two Al-related deep energy levels El and E2 in Al-doped ZnS and Al-doped ZnS.983Te.017. A third deep energy level E3 was also found in Al-doped ZnS.983Te.017 which possibly is a deep level related to the presence of Te in this alloy system. The ratios between the El and E2 concentration and the donor concentration in Al-doped ZnS.983Te.0l7 are found to be much greater than those in Al-doped ZnS.

Date of Award	1996
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology