Metastable defects in Si3N4 layers accessed by scanning photoluminescence

Abstract

We report on spectroscopic photoluminescence (PL) mapping performed at room temperature in commercial grade multi-crystalline silicon ribbon wafers for solar cells. Besides a standard band-to-band luminescence of silicon with maximum at 1.09eV, a broad visible PL band at 1.94eV is observed under UV excitation on wafers covered with Si3N4 layer. Scanning PL was applied consecutively to both PL bands. We observed that the intensity and topography of the visible PL are not related to the band-to-band luminescence, but rather determined by parameters of Si3N4 deposition. The visible PL band exhibits a reversible photoquenching of the intensity under 325nm HeCd laser. The PL intensity can be recovered by annealing with the rate showing a thermally activated behavior. The observed PL photoquenching reveals a metastable process in Si3N4 film. We demonstrate the possibility to create a reversible luminescence pattern on the Si3N4 layer using UV laser beam.