The EPR and luminescence of porous silicon

The data on the EPR, photoluminescence (PL), and current transfer in porous silicon (PS) on KDB-0.3 and KES-0.01 Si, which was oxidized by 10-min isochronous thermal annealing in air at temperatures $T_{\operatorname{ann}}$ from 20 to 900$^\circ$C, as well as in HNO$_3$, are presented in order to further clarify the nature of Pb centers of nonradiative recombination. The maximum PL quantum yield was observed during the chemical oxidation of PS on KDB-0.3 silicon. An anticorrelation of the PL and EPR intensities of Pb centers is observed in the range $T_{\operatorname{ann}}$ = (20 – 300)$^\circ$C. A nonmonotonic dependence of the EPR intensity of Pb centers on $T_{\operatorname{ann}}$ with a minimum at approximately 700$^\circ$C is revealed. The weak PL of PS with $T_{\operatorname{ann}}$ of $\sim$700$^\circ$C accompanied by a minimum EPR signal from Pb centers means that other nonradiative-recombination centers arise after annealing. A decrease in the PS conductivity with an increase in $T_{\operatorname{ann}}$ is associated with the decomposition of Si fibers in PS into small granules, through which discrete tunneling of current carriers occurs.