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Determination of free standing porous silicon energy gap by absorption coefficient

R. S. DARIANI1,* , R. ZAFARI1

Affiliation

  1. Department of Physics, Alzahra University, Tehran, 1993893973, Iran

Abstract

Porous silicon (PS) nano crystals were made from p-type Si wafer by electrochemical anodization at etching times of 10, 20, 30, and 40 min. SEM images of samples from top and cross section showed that porous layer thickness and porosity increase with increasing etching time. PS layers were lifted off from Si wafer by mechanical method and put on glass lamel. Free standing structures are interesting because absorption spectra can be measured on the samples. Absorbance (ABS) of the samples were measured by spectrophotometer and showed it decreases with increasing etching time. Absorption coefficient calculated from absorbance by α=ABS/(dloge) relation, where d is PS layer thickness. Energy gap of the samples has been obtained from (αhv) 1/2 and (αhv) 2 curves versus hv which they confirm that free standing porous silicon (FPS) has quasi-direct energy gap like porous silicon. Also extinction coefficient of the samples were calculated from equation and showed that it decreases with increasing porosity..

Keywords

Free standing porous silicon, Absorption coefficient, Energy gap, Quantum confinement, Blue shift.

Submitted at: Nov. 24, 2013
Accepted at: Nov. 13, 2014

Citation

R. S. DARIANI, R. ZAFARI, Determination of free standing porous silicon energy gap by absorption coefficient, Journal of Optoelectronics and Advanced Materials Vol. 16, Iss. 11-12, pp. 1351-1355 (2014)