Thermal annealing of porous silicon to develop a quasi monocrystalline structure

Low porosity (similar to 20-30%) porous silicon produced by electrochemical anodization was annealed in the temperature range 1000-1150 A degrees C under pure hydrogen atmosphere and under hydrogen mixed with nitrogen in different proportions for a duration of 15-60 min. Porous silicon was transformed to quasi monocrystalline porous silicon (QMPS) in the temperature range 1050-1100 A degrees C under pure hydrogen atmosphere. The crystallinity was confirmed by grazing incidence X-ray diffraction. Field emission scanning electron microscopic (FESEM) studies revealed that the surface layer is pore free with a few voids embedded inside the body. Atomic force microscopic (AFM) studies confirmed relatively smooth and uniform surfaces under the same annealing conditions. Our experimental results concluded that the recrystallization of porous silicon at 1100 A degrees C and in presence of pure hydrogen exhibits lower reflection loss compared to bulk crystalline silicon. Also the electrical resistivity of QMPS makes it suitable for optoelectronic devices and solar cells.