Four-probe technique electrical resistivity distribution over grinded specimen surface: (a) initial textured surface, ρav = 1.57±0.11 Ohm×cm; (b) surface with porous layer formed in 5 min, ρav = 1.91±0.14 Ohm×cm; (c) same with 10 min etched porous silicon layer, ρav = 2.18±0.13 Ohm×cm; (d) same with 15 min etched porous silicon layer, ρav = 2.3±0.4 Ohm×cm.