Impedance measurement for microstructure characterization and internal surface estimation of macroporous silicon

Abstract

In this paper, a simple and convenient method based on impedance measurement has been proposed for the first time to evaluate the average porosity, pore radius, and internal surface area of macroporous silicon structure fabricated by electrochemical method. The porosity and the average pore radius have been obtained by developing a geometrical model and applying the generalized effective medium approximation theory to the dc and ac impedance measurement of both unoxidized and thermally oxidized macroporous silicon. The internal surface area per unit volume is then computed from the porosity and the pore radius using the same model. The method has been applied to a wide range of porosity from 30 to 58% fabricated on p-type <100> silicon with a resistivity of 10-20 V cm. Experimental verification of porosity, mean pore radius, and internal surface area have been performed by standard gravimetric technique and by top-view and crosssection SEM imaging, respectively. A typical mean pore radius, porosity, and internal surface area of a macroporous silicon sample has been obtained to be 1.52 mm, 54.2%, and 3565.7 cm 2 /cm 3 , respectively, from the impedance measurement and 1.5 mm, 55%, and 3666.7 cm 2 /cm 3 from SEM and gravimetric analysis which shows that the results are within 2% of the values obtained by conventional methods. The advantages of this method over the other recently reported techniques for similar characterization have been discussed.

Properties of bilayer contacts to porous silicon

“…Although several electrical equivalent circuits may be used to explain the behavior of these structures all of them use at least a resistor placed in parallel with a capacitor [13,31] to explain the observed behavior. When an Au film is grown over the NiCr, the above model still works properly, but the resistance placed in parallel becomes larger due to the Au/NiCr interface barrier.…”

AC Impedance Studies on Metal/Nanoporous Silicon/p-Silicon Structures

“…There exists a good agreement within 2% accuracy between these results and the values obtained from conventional methods such as SEM and gravimetric analysis. 13 AC measurements on gold (Au)/PS/p-Si/Al using the DC bias voltage between ±2 V have been made at room temperature only and over the frequency range of 5 Hz-10 kHz. The structure exhibits conductor-type behavior for the bias voltage up to 0.5 V while the diode-type conduction becomes dominant at the medium frequency range.…”