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We investigate Si nanocrystals fabricated by the rapid thermal oxidation (RTO) of an ultrathin chemical vapour deposition (CVD) amorphous Si (a-Si:H) film. It is found from the transmission electron microscope (TEM) observation that the ultrathin RTO film contains Si nanocrystals of around or less than 5 nm in size. The dynamic electrical conduction measurement of the RTO diode structure including the Si nanocrystals reveals novel features such as the N-shaped tunnel current versus gate voltage characteristics and the hysteresis. It is also found that the gate voltages at the first and second current rise are fixed and the current reduction in the fixed time interval is observed at the constant gate voltage. These findings can be explained by the fixed-amount electron charging effect at the Si nanocrystals and the consequent screening effect on the tunnel current flowing through the diode structure.

A new technique of surface passivation of silicon substrates by quinhydrone/ethanol treatment has been investigated. To estimate the surface passivation effect, the lifetimes of the silicon substrates were measured using the microwave photoconductive decay method. The measured lifetimes were dependent on quinhydrone concentration and passivation time. The 0.01 mol/dm3 quinhydrone/ethanol treatment showed a good passivation effect, and a very low surface recombination velocity was obtained. The quinhydrone/ethanol treatment was a more effective passivation technique than the iodine/ethanol treatment. Therefore, the quinhydrone/ethanol passivation can be widely used for lifetime measurement.

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Surface passivation of crystalline silicon (c-Si) is experimentally studied during the growth of a hydrogenated amorphous silicon (a-Si:H) and epitaxial silicon (epi-Si) passivation layer at a subnanometer to nanometer scale. The property of surface passivation is monitored in real time via in situ measurement of a photocurrent in c-Si under plasma-enhanced vapor deposition for the passivation layer growth. The measurement results suggest the following. Passivation is improved by the growth of an a-Si:H layer, where a large band offset is formed at the a-Si:H/c-Si interface, and the carrier recombination is suppressed. On the other hand, passivation is deteriorated with the growth of an ultrathin epi-Si layer (d≲2.5±1.0 nm) because the band offset is not formed at the interface, and plasma-induced defects are created in c-Si. However, passivation is improved with a thick epi-Si layer (d≳2.5±1.0 nm), where the band bending is formed near the epi-Si/c-Si interface, which partially suppresses the carrier recombination. The suppression of the plasma-induced defects as well as the formation of the band offset are important for surface passivation.