Role of sulfur vacancies on the electrical characteristics of sputtered films of ZnS

Films of zinc sulfide (ZnS) have been grown on silicon (Si) substrates by sputtering in argon and either sulfur-enriched or deficient-gaseous environments. The density of electron traps at the ZnS/Si heterojunction is invariant with gas. However the photoluminescent intensity increases for films grown in argon enriched with hydrogen sulfide (Ar:H2S) compared with those grown in argon. Furthermore the density of sulfur vacancies is reduced by the presence of H2S, particularly compared with films grown in a mixture of argon and hydrogen (Ar:H). In these latter films sulfur vacancies increase the electrical conductivity by approximately three orders of magnitude. It is expected, therefore, that the high field condition essential for hot-electron production in thin film electroluminescent devices is optimized in films with a reduced sulfur vacancy content, i.e., grown in Ar:H2S.