Influence of Pyridine Molecule Adsorption on Concentrations of Free Carriers and Paramagnetic Centers in Porous Silicon Layers

Abstract

The influence of adsorption of donor pyridine (C5H5N) molecules on free-hole and defect concentrations in porous silicon layers differing in the morphology of composing nanocrystals and pores, as well as in the boron doping concentration, was studied using infrared and electron spin resonance spectroscopy. It was shown that the dependence of the hole concentration on the pyridine vapor pressure is controlled by the initial boron doping level of porous silicon, while the number of defects, i.e., dangling silicon bonds, is almost unchanged during adsorption for all sample types. For samples on substrates with a boron concentration of ∼1020 cm−3, a decrease in the number of holes at low pyridine pressures is observed and is attributed to hole capture by surface states of adsorbed C5H5N molecules. At pyridine pressures close to the saturated vapor pressure, the hole concentration in porous silicon layers increases, which is associated with hole “trap” depopulation due to an increase in the permittivity of the silicon nanocrystal neighborhood under conditions of C5H5N vapor condensations in sample pores.