Simulation of the photocurrent behavior at laser excitation in metal/nanocrystalline Si-p-Si structures: novel IC compatible optical sensor

The physical model for metal/nanocrystalline Si-p-Si structure has been developed. It takes into account: (i) the theoretically predicted band-gap variation of nanocrystalline Si (nc-Si) with decreasing of nanocrystalline sizes; (ii) the offset between conduction bands of nc-Si and bulk p-Si is the major one ; (iii) Schottky barrier is formed in the p-Si space charge region (SCR). Modeling of photocurrent behaviour on the basis of this model at laser excitation with 1,96 eV permitted to reveal that the photocurrent threshold is defined by electrons from p-Si over the barrier formed by the band offset. This effect is observed at the nc-Si thickness considerably less than the width of light penetration in p-Si 1/¿ and carrier generation in the SCR mainly. The photocurrent threshold for the metal/nc-Si-p-Si structure is determined by nanocrystalline sizes. The developed physical model was directly confirmed by STM with local I-U curve measrements.