Variable Range Hopping Conduction in Semiconductor Nanocrystal Solids

The temperature and electrical field dependent conductivity of n-type CdSe nanocrystal thin films is investigated. In the low electrical field regime, the conductivity follows σ∼exp([-(T^*/T)^1/2] in the temperature range 10<T<120 K. At high electrical field, the conductivity is strongly field dependent. At 4K, the conductance increases by 8orders of magnitude over one decade of bias. At a very high field, conductivity is temperature independent with σ∼exp([-(E^*/E)^1/2]. The complete behavior is very well described by variable range hopping with a Coulomb gap.