Germanium nanocrystal density and size effects on carrier storage and emission

We are interested in germanium nanocrystal density and size effects on the carrier storage and emission processes. For this purpose, high frequency capacitance-voltage and current-voltage characteristics were performed for temperatures varying from 300 to 77 K. Ge nanocrystals were deposited on a silicon dioxide/p-doped silicon structure and capped with a thin amorphous silicon layer. Results evidenced an electron storage phenomenon in nanocrystals that presented two different behaviors depending on the temperature. For temperatures higher than ∼140 K, the storage was mainly controlled by the nanocrystal density. At low temperatures the storage was reduced due to lowering of the tunneling barrier that resulted from a carrier quantum confinement process. Thermal activation energy of the carrier emission process was revealed as varying linearly with nanocrystal energy band gap. Activation energy was identified as a barrier height to be overcome by the emitted electrons.