Optically enhanced trap assisted hysteretic I-V characteristics of nanocrystalline silicon based p-i-n heterostructure

Abstract

A p-i-n heterostructure containing electrochemically synthesized silicon (Si) nanorods embedded in a nonstoichiometric silicon oxide matrix sandwiched as i-layer between p-Si and n-type hydrogeneted amorphous Si shows hysteresis in both forward and reverse biases with an additional switching in forward bias. Conductivity in the trace path is lesser than the retrace path. Hysteresis in the reverse bias has been found to get enhanced up to three orders of magnitude under illumination by laser sources of different intensities and wavelengths showing the potential of the structure as an effective memory device. Hysteresis area and conductivity become maximum for red light and gradually decrease for green and violet light for fixed intensity. It is well known that the Si nanocrystal–silicon oxide interface contains a lot of electron and hole trap levels within the bandgap. Trapping and detrapping of photogenerated carriers at the trap/defect states are expected to affect the band bending at the junctions. The observed optically enhanced hysteresis has been explained through formation and destruction of the potential barrier at junctions during trace and retrace paths, respectively. The potential has been estimated by solving Poisson's equation, and the current–voltage (I–V) relation for trace and retrace paths has been derived where the rate of trapping and detrapping becomes different resulting in the observed hysteresis. Theoretically obtained I–V characteristics match well with the experimentally obtained results. The trap density in the i-layer estimated to be ∼1011/cm2 is in good agreement for the trap density in similar systems.