Atomic Layer Deposition of Transparent and Conducting p-Type Cu(I) Incorporated ZnS Thin Films: Unravelling the Role of Compositional Heterogeneity on Optical and Carrier Transport Properties

Optically transparent and highly conducting p-type Cu(I) incorporated ZnS (Cu:ZnS) films are deposited by stacking individual layers of CuS and ZnS using atomic layer deposition. The deposition chemistry and growth mechanism are studied by in situ quartz crystal microbalance. Compositional disorder in atomic scale is observed with increasing Cu incorporation in the films that results in systematic decrease in the optical transmittance in the visible spectrum. Again the conductivity also emphatically depends on the volume fraction of phase-segregated conducting covellite phase. An illustrious correlation prevailing the interplay between the optical transparency and the charge transport mechanism is established. The hole transport mechanism that indicates insulator to-metal transition with increasing Cu incorporation in the composite is explained in terms of an inhomogeneously disordered system. Under optimized conditions, the material having moderately high optical transmission with degenerate carrier concentration lies exactly at the confluence between the metallic and insulating regime. The lowest resistivity that is obtained here (1.3 x 10(-3) Omega cm) with >90% (after reflection correction) transmission is highly comparable to the best reported in the field and probably analogous to the commercially available n-type transparent conductors.