Effect of duty cycle and frequency on the morphology of porous silicon formed by alternating square pulse anodic etching

Abstract

AbstractIn this work we report the fabrication and characterization of porous silicon formed by alternating square pulse anodization. The effect of duty cycle (5–100%) and frequency was studied for porous silicon samples made with highly doped silicon wafers, under the same equivalent charge condition. The high resolution scanning electron microscopy images reveal that, under the same conditions of current and frequency, there exists an optimum value of duty cycle (20%), at which the structure exhibits superior characteristics. Maintaining the same charge supplied during the positive square pulse for the total anodization time, with a 10 mA/cm2 current density and 5% duty cycle, samples were fabricated at different frequencies (from constant current to 100 Hz) and the etching rate/thickness of the PSL formed at a 10 Hz frequency is found to be maximum, indicating that the response of the electrochemical reaction is maximum at this frequency. However, a reduction in the interface roughness between porous silicon and crystalline Si is obtained only at high frequencies. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)