Thermally stimulated luminescence in porous silicon

Abstract

The low-temperature thermally stimulated luminescence (TSL) in both porous silicon (PS) layers on Si substrate and PS powder has been found in the 4.2–300 K temperature range. The dependence of the TSL effect on the wavelength and temperature of an excitation was studied in detail. The shape of TSL glow curves displays the quasicontinuous spectrum of the electron states in the gap of PS and the activation energy is subject to the linear law of E[eV]=0.0029T−0.14 at T>70 K. For the homogeneous PS powder, the TSL glow curves weakly depend on an excitation wavelength. For the PS layer on Si substrate the maximum of the TSL glow curve shifts to the higher temperature both at the excitation by the short wavelength light and by the supplementary exposition to IR illumination. Such behavior is stipulated by the gradient of the PS energy band gap with the depth and, consequently, by the reconstruction of electron states in the band gap. It is shown that the TSL is conditioned by the photoluminescence (PhL) in PS bulk, and the spectral distribution of the TSL signal at 100–120 K is close to its PhL spectrum excited at 546 nm.