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.

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Photo-enhanced hysteretic I-V curves have been observed under reverse bias in a p-i-n structure containing electrochemically etched nanostructured silicon (Si) sandwiched between p-Si and n-type a-Si:H layers. These curves have been found to depend on intensity of incident illumination and structural morphology of the nanostructured Si layer. The conductance in trace path is lower than that in retrace path. Charge transport mechanism in this structure has been interpreted using microscopic description of charge trapping and detrapping in the defect states present at the interface of nanocrystalline silicon core and oxide shell in the active layer. An applied voltage dependent probability distribution of trapping and detrapping has been calculated in light of classical random walk problem. The trapping/detrapping of charges leading to development/destruction of potential barriers in the path of charge flow shows an analogy with the river bed deposition/erosion. The rate of trapping has been considered to depend on the empty defect states whereas the rate of detrapping depends on the already filled defects. Moreover, the rate of both trapping and detrapping is expected to depend on the charge flow rate. All these considerations lead the I-V relations for trace and retrace paths in reverse bias fitting nicely with experimental I-V loops. The observed peaks in the voltage dependent dynamic conductance in trace and retrace paths have been explained as a consequence of development and destruction of two barriers in the active layer for electrons and holes separately. Best fit values of the fitting parameters indicates that the trace path is dominated by holes whereas the retrace path is dominated by electronic transport. The difference in mobility of electron and hole leads to different trapping and detrapping rates in the two paths resulting in the observed hysteresis.

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