Chemical, Morphological and Electrical Properties of Porous Silicon Prepared by Photelectrochemical Etching

Abstract

In this work, the nanocrystalline porous silicon (PS) films is prepared by photoelectrochemical etching of n-type silicon wafer with different currents density (20, 35 and 50 mA/cm 2 ) and etching time 15 min on the formation nano-sized pore array with a dimension of around few hundreds nanometric. The films were characterized by the measurement of FTIR spectroscopy and atomic force microscopy properties.Chemical fictionalization during the photoelectrochemical etching show on surface chemical composition of PS. The etching possesses inhomogeneous microstructures that contain a-Si clusters (Si3-Si-H) dispersed in amorphous silica matrix and (O-SiO, C-SiO). It is observed from the FTIR analyses that the Si dangling bonds of the as-prepared PS layer have large amount of Hydrogen to form weak (Si-H) bonds. The atomic force microscopy investigation shows the rough silicon surface; with increasing etching process (current density) porous structure nucleates which leads to an increase in the width (diameter) of surface pits. Consequently, the surface roughness also increases. The electrical properties of prepared PS; namely current density-voltage characteristics under dark, show that the pass current through the PS layer decreased by increasing the current density and etching time, due to increase the resistivity of PS layer. The PS layer shows a rectifying behaviour with different rectification ratio. C-V measurements demonstrate that the behaviour of the resulting junction is more like to Schottky junction. This study makes it clear that the charge carries depletion process occur in PS layer. Moreover, the charge carries decrease and width of depletion layer increase by increasing the current density.

Study of Electrical Properties of Photodetector

“…Table 1 shows the ideality factor (Z) and the barrier height (eV) at different etching density. The values of the ideality factor are found to be around 4.6 to 2.3 at 15min etching time and different values of etching current density, (15,17,19, 21) mA/cm 2 . If the structure includes interface states, ideality factor becomes high, that accounts to the totality of Z of the individual rectifying junctions (i.e., the actual PSi/c-Si heterojunction and Schottky diodes at the Al/PSi or the two metal-semiconductor junctions (Al/PSi, p-Si/Al) of a diode preferably possess Ohmic features) thus resulting in the ideal factor to be higher than unity.…”

“…The schematic setup of electrochemical etching is depicted in figure 1. Sample prepared at different etching current density (15,17,19,21) …”

“…We have studied the electrical and photoelectrical characteristics of Al/PSi/p-Si/Al structure apart from investigating the effect of structural parameters of the PSi layer on these properties. By considering all these factors, the PSi layers are prepared at different etching current density (15,17,19, 21)mA/cm 2 with constant etching time of 15min for p-type silicon. Figure A1 illustrates the Schottky or heterojunction behaviour.…”

“…It relates the etching current density-voltage features of Al/PSi/pSi/Al structure formed at 15min. It is of dissimilar etching current densities (15,17,19 and 21) mA/cm 2 in which the current-voltage graphs are attained by varying the applied bias (ranging from -10 V to +10 V). Then the resultant etching current density is measured.…”

“…Figure 3 illustrates the I-V characteristics of Al/PSi/p-Si/Al sandwich model of samples made at diverse etching current density (15,17,19, 21)mA/cm² and power intensity (540, 1230 and 1800)μW/cm² with constant etching time in dark conditions at room temperature.…”