Control of charge carrier density in mesoporous silicon by adsorption of active molecules

Abstract We demonstrate that adsorption of donor‐like and acceptor‐like molecules could be used to control the free charge carrier type and density in mesoporous silicon films. Fourier‐transform infrared spectroscopy and electron paramagnetic resonance technique are used to investigate the free charge carriers and surface defects (P_b‐like centers), respectively, in porous films formed from crystalline Si substrate of different conductivity type and doping level. It is shown that the carrier type (electron or hole) and concentration in mesoporous silicon are depended on (i) molecule partial pressure, (ii) doping level of the substrate; (iii) density of defects‐silicon dangling bonds. The free hole concentration in p‐type mesoporous silicon is found to be changed in the range from 10¹⁷ to 3 × 10¹⁹ cm^–3 by the adsorption of acceptor‐like molecules. The donor‐like molecule adsorption can switch the type of major carriers from holes to electrons. The obtained results are explained by considering the adsorption‐induced formation of surface states in Si nanocrystals assembling mesoporous silicon. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)