Size-Dependent Electrical Transport in CdSe Nanocrystal Thin Films

Abstract

Electrical transport in films of CdSe nanocrystals with diameters varying from 2.9 to 5.1 nm was examined over 233-300 K by employing electrolyte gating to control the electron density. The transport parameters varied strongly and systematically with nanocrystal diameter. First, a strong correlation was observed between the device turn-on voltage and the size-dependent position of the lowest unoccupied electronic states of the nanocrystals. Second, the electron mobility increased with increasing particle diameter and reached a high value of 0.6 cm 2 /(V s) for films with 5.1 nm nanocrystals. Third, the charge transport could be described in terms of the nearest-neighbor-hopping mechanism with a size-dependent activation energy and a pre-exponential factor for mobility. The activation energy can be viewed as a size-dependent charging energy of an individual nanocrystal. Collectively, the combination of size-and temperature-dependent measurements provides a powerful approach to understanding electrical transport in nanocrystal films.

Growth of nanocrystalline thin films of metal sulfides [CdS, ZnS, CuS and PbS] at the water–oil interface

“…In the case of ZnS, lms E a s of 22.5 meV and 9.1 meV were obtained corresponding to the high (>200 K) and low (<200 K) temperature regimes. The E a s reported herein are in line with previous reports 42, 44 and suggest that charge transport is largely limited by the barrier present at the surface of the grains.…”

To Be or not to Be: Band-Like Transport in Quantum Dot Solids

“…− at temperatures from 233-300 K and QD diameters (2 ) from 2.9-5.1 nm [25]. The measured field-effect mobilities increased monotonically with 2 and reached a maximum of 0.6 cm 2 /V ⋅ s for the largest particles.…”

Electronic Impurity Doping in CdSe Nanocrystals

“…44 Because electron mobility also varies with carrier concentration, we fixed the gate-induced carrier density (at 10 14 carriers/cm 2 ) and then compared electron mobilities for films of CdSe nanocrystals with different dopant concentrations. We observed that the electron mobility first increased at low dopant concentrations and then decreased gradually with further doping, again consistent with a transition from n-to p-type doping.…”