Effect of contact with air on the photoluminescence spectrum of porous silicon

A study has been made of the transformation of photoluminescence (PL) spect ra of porous silicon (PS) induced by its ageing, including the early stages of contact with air. The sample was prepared under conditions that minimiz ed this contact, and spectral measurements were carried out in a high vacuu m or in liquid nitrogen. The PS PL spectra obtained under continuous measur ement in high vacuum are always dominated by one emission band of PS nanoel ements, which shifts toward shorter wavelengths with ageing by 150 nm. At 8 0 K, the band intensity is considerably higher than at 300 K, and this diff erence grows with ageing. Exposure of a sample to air for a few tens of sec onds is long enough to strongly transform its time-resolved PL spectra, whi ch is evidence of a change in the sample surface. The effect of immersion o f PS samples in liquid nitrogen on PL spectra is associated not only with t heir cooling, but also with the field of adsorbed nitrogen molecules, whose influence becomes weaker with increasing thickness of the oxidized near-su rface layer. The variation of the spectral properties and kinetics of the l ong-wavelength PS PL band with temperature, medium (liquid nitrogen or vacu um), and exposure time suggest that these factors affect carrier migration between silicon nanoelements. (C) 2000 MAIK "Nauka/Interperiodica".