DEFECTS IN HOT-WIRE DEPOSITED AMORPHOUS-SILICON - RESULTS FROM ELECTRON-SPIN-RESONANCE

A series of hot-wire deposited amorphous silicon films with hydrogen c ontent varying between 0.5 and 17 at.% has been studied systematically with different experimental techniques. Steady-state photocarrier gra ting measurements on the samples indicate excellent ambipolar diffusio n lengths even for films with smaller hydrogen contents. Sub-bandgap a bsorption indicates low defect densities for samples with a hydrogen c ontent larger than 1 at.%. Electron spin resonance measurements on the se samples, however, yield larger volume average spin densities than e xpected for the intermediate range of hydrogen content, 1 at.% < C-H < 8 at.%. A series of samples with different thicknesses indicates a de fective layer at one or both of the interfaces and a bulk spin density which agrees well with the optical absorption measurements. We believ e that the defective layer is due to outdiffusion of hydrogen at the s ubstrate interface during growth at temperatures, as indicated by seco ndary ion mass spectroscopy measurements on the same samples. (C) 1998 Elsevier Science B.V. All rights reserved.