Origin of photo-enhanced hysteretic electrical conductance in nanostructured silicon-based heterojunction

Abstract

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.

Negative differential resistance in Si nanostructure: role of interface traps

“…These interfacial traps are considered to play a detrimental role during charge conduction, in general [1,19]. However, in some cases the interfacial traps are found to be advantageous due to their dominance in charge conduction which results in development of some special features in I-V characteristics like switching, hysteresis etc [19,24,25]. In this work, we have explained the NDR in light of trap-dominated charge conduction mechanism resulting in a good agreement between experimental and theoretically calculated results.…”

“…The origin of PL from nanostructured silicon is still a topic of debate [47-52, 56, 57]. However, it is grossly accepted that the reason for intense visible emission from nanostructured silicon is due to the transition between the edges of the conduction and valance bands of the widened gap due to quantum confinement [17,42,51,58] as well as the mid gap defect states at the interface of the nonstoichiometric silicon oxide and the nanocrystalline core [19,24,42,48,56,57] as shown in figure 12(a). It has been shown by many groups that the peak falling in the red region (∼600 nm) is due to transition between the oxide related electron trap states to the valance band edge [42,51,58].…”

“…Si nanostructure in different forms is a well-researched material from the discovery of photoluminescence from it [17]. Then the studies on charge transport through Si nanostructures got lagged [18,19] in comparison to the studies on photoluminescence due to primarily two reasons. First reason is the inevitable presence of insulating oxides of Si around the freshly prepared Si nanostructures resulting in low efficiency in case of electroluminescence [20,21].…”

“…First reason is the inevitable presence of insulating oxides of Si around the freshly prepared Si nanostructures resulting in low efficiency in case of electroluminescence [20,21]. Secondly, the role of surface defects/traps present at the nanocrystalline core and oxide shell in charge conduction is not well-explained till date [19,[22][23][24][25]. These interfacial traps are considered to play a detrimental role during charge conduction, in general [1,19].…”

“…Secondly, the role of surface defects/traps present at the nanocrystalline core and oxide shell in charge conduction is not well-explained till date [19,[22][23][24][25]. These interfacial traps are considered to play a detrimental role during charge conduction, in general [1,19]. However, in some cases the interfacial traps are found to be advantageous due to their dominance in charge conduction which results in development of some special features in I-V characteristics like switching, hysteresis etc [19,24,25].…”