https://doi.org/10.15407/jopt.2018.53.248
Optoelectron. Semicond. Tech. 53, 248-253 (2018)
V.F. Onyshchenko, M.I. Karas’
RELAXATION OF PHOTOCONDUCTIVITY IN MACROPOROUS SILICON
The paper presents the diffusion model of photoconductivity relaxation and the simple expression that determines the photoconductivity relaxation time in macroporous silicon. The model of photoconductivity relaxation in macroporous silicon takes into account the inhomogeneity of the generation of excess charge carriers in the sample, the penetration of light into the macropores, and the illumination of the single-crystal substrate through the bottom of the macropores. The relaxation of photoconductivity is determined by the recombination of excess charge carriers on the pore surface and is limited by the diffusion of charge carriers from the substrate into the recombination surfaces. The photoconductivity relaxation time in macroporous silicon with and without substrate is found from the nonstationary diffusion equation of minority charge carriers. The solution of the nonstationary diffusion equation written for a macroporous layer and a single-crystal substrate is complemented by boundary conditions on the surfaces of a sample of macroporous silicon and on the boundary between the macroporous layer and the single-crystal substrate. The photoconductivity relaxation time in macroporous silicon depends on such values as: volume lifetime of minority charge carriers, charge carrier diffusion coefficient, substrate thickness, average macropore diameter, average distance between macropore centers, surface recombination rate, volume fraction of macropores. The photoconductivity relaxation time in macroporous silicon is calculated and presented in the figure depending on the depth of the macropores. It is shown that the photoconductivity relaxation in macroporous silicon with through pores is similar to the photoconductivity relaxation in single crystal silicon. But in this case, the photoconductivity relaxation time in macroporous silicon corresponds to the less photoconductivity relaxation time in single-crystal silicon, as additional recombination of non-equilibrium charge carriers occurs on the surface of macropores.
Keywords: macroporous silicon, photoconductivity, kinetics, relaxation.