Electron paramagnetic resonance of dangling bond centers in vacuum-annealed porous silicon

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Abstract
Electron paramagnetic resonance(EPR) of centers produced in porous silicon(PS) by heat treatment in vacuum is investigated. Annealing in the temperature range of 400–600 °C and vacuum up to 5×10−5 Torr increases the EPR line intensity of P b centers in a way depending on the time of annealing. This can be explained by hydrogen depassivation of the P b centers. An isotropic line with g=2.0055, usually attributed to disordered Si dangling bonds, appears after vacuum annealing of some minutes but at a longer heat treatment its intensity decreases. At room temperature this decrease is exponential with a time constant of a few minutes, depending on the level of vacuum. Heat treatment of PS in vacuum leads to amplification of the P b EPR spectrum after exposition of samples to air at room temperature.