LIGHT-INDUCED DEFECTS IN PHOSPHORUS-DOPED HYDROGENATED AMORPHOUS-SILICON

Previous results on the gap-state profile of phosphorus-doped hydrogenated amorphous silicon before and after light soaking in the whole region of the gap have been re-examined. By analysis of capacitance-voltage characteristics as well as spectra of several variations of isothermal capacitance transient spectroscopy, the gap-state profiles before and after light soaking were determined quantitatively and the validity of the two-defect model is confirmed; shallower states (D-) located 0.5-0.6 eV below the conduction band edge, E(c), and deeper states (*D-) located 1.0-1.3 eV below E(c). From the results, it is clarified that the donor states (P4+) decrease after the light soaking while the gap states denoted as N(CT) located 0.25-0.35 eV below E(c) are created and *D- is simultaneously converted to D-. This conclusion is discussed in comparison to the recent defect-formation model based on the thermodynamic analysis of a few simple chemical reactions.