https://doi.org/10.15407/iopt.2019.54.112
Optoelectron. Semicond. Tech. 54, 112-118 (2019)
V.F. Onyshchenko
RELAXATION OF PHOTOCONDUCTIVITY IN DOUBLE-SIDE MACROPOROUS SILICON
Photoconductivity relaxation and photoconductivity relaxation time in double-side macroporous silicon is determined from a system of two transcendental equations. The equations are derived from the model of photoconductivity relaxation in bilateral macroporous silicon, which takes into account the penetration of light into the macropores and the illumination of the single crystal substrate and the second layer of macroporous silicon through the bottom of the macropores. The system of equations obtained by us is similar to a system of two equations describing the relaxation of photoconductivity in single-crystal silicon. The difference lies in the fact that the equations contain expressions describing the processes that occur in macroporous layers and on the verge of a macroporous layer and a single-crystal substrate. In the absence of macropores, this system of equations turns into a system of equations for determining the relaxation of photoconductivity in monocrystalline silicon. The photoconductivity relaxation time in double-side macroporous silicon is found from the nonstationary diffusion equation of minority charge carriers. The solution of the nonstationary diffusion equation written for each of the macroporous layers and the single crystal substrate is complemented by boundary conditions on the surfaces of the sample of macroporous silicon and on the boundary between the macroporous layer and the single crystal substrate. The photoconductivity relaxation time in double-side macroporous silicon depends on such values as: the volume lifetime of minority charge carriers, the diffusion coefficient of minority charge carriers, and the thickness of the single-crystal substrate between the macroporous layers. And also, the values recorded for each macroporous layer: the depth of the macropores, the average diameter of the macropores, the average distance between the centers of the macropores, the volume fraction of macropores, the rate of surface recombination. Calculations showed that photoconductivity relaxation in bilateral macroporous silicon is determined by recombination of excess charge carriers on the surface of the macropores of each macroporous layer and limited by the diffusion of charge carriers from the substrate to the recombination surfaces. The photoconductivity relaxation time in double-side macroporous silicon is calculated and shown in the figure depending on the depth of the macropores.
Keywords: double-side macroporous silicon, photoconductivity, kinetics, relaxation.