We investigate the linear response of charge stored in Ge nanocrystals (NCs) embedded in ${\text{SiO}}_2$ to an alternating electric field in order to study the electronic properties of the $\text{Ge-NC}/{\text{SiO}}_2$ interface. Experimentally, the modulation of the cluster charge is sensed by the transient drain current of field-effect transistors in whose gate oxide the nanocrystals are embedded. For interpretation of the experimental results, we present a small-signal model obtained from a first-order expansion of the general quantum-mechanical description of the system. The contribution of trap states to the alternation of the cluster charge is distinguished from that of quantized states in the NC conduction band by calculating the latter one by density functional theory and subtracting it from the experimental values. A high $\text{Ge-NC}/{\text{SiO}}_2$ interface density of $2.8\times {10}^{13}{\text{cm}}^{-2}{\text{eV}}^{-1}$ is obtained. These traps cannot be passivated efficiently by a hydrogen anneal at $450°\text{C}$ and mediate efficient nonradiative recombination processes.

• Received 28 June 2010

DOI:https://doi.org/10.1103/PhysRevB.82.195415