GENERAL BRONSTED ACID BEHAVIOR OF POROUS SILICON - A MECHANISTIC EVALUATION OF PROTON-GATED QUENCHING OF PHOTOEMISSION FROM OXIDE-COATED POROUS SILICON

Photoinduced visible light emission from porous silicon can be reversi bly quenched by a wide variety of chemical species. The growth of a th in layer of oxide on the porous silicon surface disrupts the quenching ability of most species, narrowing down the number of quenchers to in clude primarily those which act as Bronsted bases. Electron paramagnet ic resonance spectroscopy, infrared spectroscopy, photoluminescence da ta, and surface chemistry suggest a quenching mechanism which involves the extraction of a nonspecifically attached proton in the oxide laye r upon exposure to base. This proton is loosely affiliated with a surf ace defect of the P-b type. This defect serves as a hole trap in the a bsence of a proton providing a nonradiative relaxation pathway. Howeve r, when a proton is present in the oxide layer, Coulombic interactions force the hole trap into a state which falls below the bandgap, allow ing for efficient radiative recombination of electron-hole pairs. The electron paramagnetic resonance spectroscopy data also demonstrate tha t there are at least two distinct mechanisms of luminescence quenching of porous silicon.