Nanocalorimetric investigation of light-induced metastable defects in hydrogenated amorphous silicon

The electrical properties of hydrogenated amorphous silicon, a-Si:H, are degraded by light-induced metastable defects after exposure to visible light for extended periods. Using nanocalorimetry, we have directly measured the heat released when these defects are annealed. Although these low level measurements were close to the instrument noise limit, and were affected by extraneous signals from adsorbed gas, a total heat release of only a few tens of nJs could be resolved. For a heating rate of 12 000 K s−1, a single broad peak of heat release, centered at 180 °C, was observed. The integrated heat release indicates that ∼8 × 1016 defects cm−3 h−1 were generated. Polycrystalline Si samples, in which no defects are created by light-soaking, showed no heat release.