Onyshchenko V. Nonequilibrium charge carriers in macroporous silicon structures.

The thesis deals with nonequilibrium charge carriers and their distribution in macroporous silicon structures on a silicon single-crystal substrate. It is established that the effective conduction of macroporous silicon structures decreases as the concentration and volume fraction of macropores increase. The effect of reduction of the space charge region width as the macropore diameter decreases is taken into account. The photocarrier effective lifetime in macroporous silicon structures is calculated analytically. It depends on the photocarrier lifetimes in the single-crystal silicon bulk and at the macropore surface. The reciprocal of nonequilibrium charge carrier lifetime at the macropore surface is the product of surface recombination velocity by the ratio between the macropore surface and silicon matrix volume. It is found that the photocarrier lifetime in silicon substrate decreases due to recombination in the macroporous silicon layer. The relaxation time of the charge carrier mobility in the macroporous silicon layer is almost three orders of magnitude bigger than that of photoconductivity. The stationary distribution of the concentration of nonequilibrium charge carriers in the macroporous silicon structure on single-crystal silicon substrate is calculated depending on the macroporous layer thickness and surface recombination velocity. It is found that symmetry of distribution of nonequilibrium minority carriers in the single-crystal silicon substrate is disturbed and carrier concentration decreases due to recombination of photocarriers on the surface of macropores. It is found that the relative photoconductivity is determined by the recombination processes at the macropore surface; it peaks at a distance between the macropore edges equal to the thickness of two Schottky layers. The photoconductivity relaxation time in macroporous silicon structures is determined by the barrier mechanism, and its relaxation obeys the logarithmic law. A negative photo-emf was measured in macroporous silicon structures at photon energies comparable to the energy of indirect.