ESR Study of Porous Silicon

Abstract

A detailed ESR study has been performed on porous silicon on both <100> and <111> p-type silicon substrates prepared using anodization in HF under a range of conditions and the results are correlated with the light emission properties. It is found that the ESR spectra are dependent upon the orientation of the samples. The ESR defect centers are identified to be the P_b centers or P_b0 centers of the Si-SiO₂ system from the g-value anisotropy maps. The variation of the spin density N_s with annealing conditions has also been studied for samples annealed either in nitrogen or oxygen ambient at 200°C for various time intervals. It is concluded that the increase or decrease of N_s are due to the generation or elimination of the P_b or P_b0 centers in conjunction with the oxidation process during annealing. From PL study of these samples, it is found that there is no simple correlation between the spin density and the PL intensity. However, a blue shift in the PL peak position was observed both in samples after a post-annealing etch in HF solution, and in samples annealed in oxygen without a post-annealing etch. This blue shift supports the quantum confinement model of light emission from porous silicon.