ADSORPTION-INDUCED MODIFICATION OF SPIN AND RECOMBINATION CENTERS IN POROUS SILICON

Electron paramagnetic resonance (EPR) and photoluminescence (PL) techn iques were employed to investigate the influence of molecules adsorpti on (H2O, O-2, C2H5OH, C-2(CN)(4)) on properties of porous silicon (per -Si). A photoinduced decrease (H2O atmosphere) and increase (O-2 atmos phere) of the silicon dangling bond concentration N-DB were detected w hile PL enhancement (H2O) and quenching (O-2) took place. Decrease of N-DB and quenching of the PL was observed under C2H5OH adsorption. Ads orption of C-2(CN)(4) did not change the EPR signal of the DB. A new E PR signal of [C-2(CN)(4)](-) radicals appeared and the PL intensity de creased dramatically at the same time. The results are discussed on th e basis of three main mechanisms of the influence of molecules on the per-Si PL properties: (i) chemical and photochemical modification of r ecombination centers (H2O and O-2); (ii) dielectric exciton quenching (C2H5OH); and (iii) destruction of excitons by strong Coulomb fields o f the adsorbed molecules (C-2(CN)(4)).