Extraction of the trap density and mobility in poly-CdSe thin films

Abstract

Polycrystalline-CdSe films with 300 and 600 Å thickness deposited by thermal evaporation and encapsulated with sputtered silicon dioxide were successively annealed in oxygen at 400°C to reduce the carrier concentration. The carrier density and Hall mobility were measured at each step. The trap density and intragrain mobility have been extracted by applying the one-dimensional grain-boundary model. These two parameters were then used as inputs to the simulation package ATLAS, which considers the conduction in both the grain and grain-boundary. The one-dimensional simulated results confirmed the value of the trapping state density obtained by using the grain-boundary model. The mobility in the simulation which gave the best fit to experimental data was lower than that extracted by the grain-boundary model. The trap density was found to be 8.2±0.5×10 11/cm 2 and 7.5±0.5×10 11/cm 2, and from the simulation the intragrain mobility was 110 and 230 cm 2/V-s for 300- and 600-Å-thick CdSe films, respectively. The simulated conductivity showed good agreement with experimental results.