Observation of charge screening in semiconductor nanocrystals

Charge screening in semiconductor nanocrystals is observed using a technique based on the optical erasure of optically encoded second-harmonic generation in semiconductor microcrystallite-doped glasses. The optical erasure rate for illumination above the band gap (ħω>${\mathit{E}}_{\mathit{g}}$) is dominated by the recombination of charges trapped outside the nanocrystals with photogenerated free carriers. The measured erasure rate is found to decrease with increasing intensity at photogenerated carrier concentrations which correspond to screening lengths of the order of the crystallite diameter. Rate calculations based on the recombination of electrons, trapped outside the crystallite, with quantized hole states, perturbed by a screened electric field, correctly predict the observed behavior.