Microscopic Understanding of the Carrier Transport Process in Ge Nanocrystals Films

Abstract

Hydrogenated amorphous germanium (a-Ge:H) films were prepared by a plasma enhanced chemical vapor deposition (PECVD) technique. Ge nanocrystals (Ge NCs) films were obtained by thermal annealing of the as-deposited samples at various temperatures. P-type behavior in Ge NCs films without any external doping was attributed to the holes accumulation caused by acceptor-like surface states. It can be found that the dark conductivity and Hall mobility reached as high as 25.6 S/cm and 182 cm2/V·s in the Ge NCs film annealed at 500°C, which were increased by over four and three orders of magnitude higher than that of the as-deposited film (1.3 × 10-3 S/cm and 0.14 cm2/V·s, resp.). Carrier transport mechanisms of Ge NCs films association with the microstructural characteristics were investigated. Three kinds of temperature-dependent conductivity behaviors, which exhibit the linear relationships of ln⁡σ versus T-1/4, T-1/2, and T-1, respectively, were observed in the temperature regions from 10 K to 500 K, showing different microscopic mechanisms governing carrier transport in Ge NCs film.