The defect density in hydrogenated amorphous material which had been doped p-type by using Al, Ga or In was studied as a function of the dopant impurity concentration by using photo-thermal deflection spectroscopy. It was found that the defect density remained roughly constant for increasing impurity concentrations of up to 2 x 1019/cm3, and increased linearly with higher concentrations of Al, Ga or In. On the other hand, the dependence of the defect density upon the Fermi energy (as deduced from conductivity data) was different for the various dopants. This was contrary to the predictions of charge-induced weak-bond to dangling-bond conversion models. A mechanism which involved direct dangling-bond formation due to sp2 bonded dopant impurities accounted qualitatively for the observed results.

D.Comedi, I.Chambouleyron: Applied Physics Letters, 1996, 69[12], 1737-9