Influence of HF concentration and current density on characteristic morphological features of mesoporous silicon

Abstract

This report explores the variations in morphological features of electrochemically fabricated mesoporous silicon as a function of two important fabrication parameters, HF concentration and current density. Four set of samples corresponding to four different HF concentrations (15%, 25%, 35% and 45% HF) were prepared with systematically varied current density (10, 20, 30, 60 and 100 mA/cm2). The effect of these parameters on many significant features like mean pore diameter, mean neighbor distance, pore count per unit area, surface roughness, surface area etc. of resulting mesoporous structure have been determined by very sophisticated UHV SPM (Omicron VT AFM XA) in contact mode. The analysis has been performed using Scanning Probe Image Processor (SPIP Version 6.0.9). The AFM analysis is supported by the results of FESEM JSM 7600F and DXR Raman Microscope. The comparative study shows that some features are more sensitive to HF concentration while others seem to depend more on current density. Pore diameter varies mainly with HF concentration while pore depth varies largely with current density. Exceptionally high pore count (450pores/100 nm2) is found at 45% HF while samples have higher average roughness (3.5 nm) at 15% HF. Sponge like layer is formed at lower current density while well aligned very straight channels are formed at higher current density. Some very interesting regimes found at high current density conditions, recorded by FESEM have also been discussed to develop more understanding of porous silicon formation mechanism.