Strongly phonon-bottlenecked spin-lattice relaxation of dangling bonds in sputtered a-Si evidenced by chemical etching

CW saturation ESR experiments at 20.9 and 9.0 GHz have been carried out between 4.2 and 300 K on a-Si films sputtered on fused silica substrates. The ESR signal (of g = 2.0050 ± 0.0001) ascribed to dangling bonds in the a-Si network shows up to be strongly saturatable (onset of saturation at K-band microwave power PS ≲ 1μW at 4.2 K). Submitting the a-Si film subsequently to a SiO2 chemical etchant drastically decreases (PS increased by more than a factor 1500) the saturatability from where a strongly phonon-bottlenecked (PBN) spin—lattice relaxation regime is concluded to exist on the non-etched films. This PBN is ascribed to O2 contamination, enhancing the saturatability in two steps.