Measurements and calculations of the valence band offsets of SiOx/ZnS(111) and SiOx/CdTe(111) heterojunctions

Abstract

SiO x (x>1.5) overlayers have been in situ grown on ZnS (111) and CdTe (111) substrates. Synchrotron radiation photoemission spectroscopy has been used to measure the electronic structures and band lineups of these two heterojunctions. The valence band offsets of SiOx/ZnS(111) and SiOx/CdTe(111) derived from the measurements are 2.8±0.2 and 4.7±0.2 eV, respectively. Harrison’s “tight binding” theory is extended into the theoretical estimation of the band lineups of SiO2 related heterojunctions. The agreement between the experimental and theoretical results is good. Our result also explains the positive role of SiO2 layers in ZnS-based thin film electroluminescence devices.

Thin SiO2 coating on ZnS phosphors for improved low-voltage cathodoluminescence properties

“…SiO 2 was used as the coating material because of its favorable band alignment when forming a heterojunction with ZnS. 4 Furthermore, SiO 2 , which consists of light elements and has low density, exhibits minimal losses in electron penetration and has a penetration depth nearly twice as large as ZnS. In the CRT manufacturing process, SiO 2 coating of ZnS phosphors is routinely performed to improve dispersion and adhesion properties.…”

“…Ban et al showed that SiO 2 forms a heterojunction with ZnS with nearly equal conduction band and valence band offsets of 2.4 and 2.8 eV, respectively. 4 The wide band gap SiO 2 layer with a positive conduction band offset relative to ZnS is then expected to reflect the electrons generated by the incident electron beam from the defective high surface recombination velocity region back into the phosphor. It is also possible that the SiO 2 could passivate surface recombination centers.…”