EFFECTIVE CORRELATION ENERGIES FOR DEFECTS IN A-C-H FROM A COMPARISONOF PHOTOELECTRON YIELD AND ELECTRON-SPIN-RESONANCE EXPERIMENTS

Amorphous hydrogenated carbon films (a-C:H) were deposited by r.f. pla sma CVD from methane, varying the self bias potential of the substrate electrode by means of the r.f. power coupled into the discharge. Film s were characterized by IR and optical spectroscopy, confirming a tran sition from polymer-like to diamond-like (DLC) material with increasin g self bias. One set of samples was investigated in situ by photoelect ron and photoelectron yield spectroscopy, from which the density of ga p states and their spectral distribution was derived. An identical set of samples was then examined by electron spin resonance to determine the density of paramagnetic defects. From a comparison of the results of both experiments, a lower limit for the effective correlation energ y of the defect states was extracted which gave surprisingly large val ues for the correlation energy of the DLC material. In addition to the interpretation of the results within a spatially uniform model, the i nfluence of a possible surface band bending on the evaluation of the c orrelation energies is also discussed.