Determination of surface states distribution in a-Si:H using MOS tunnel Junctions

The measurement of the tunneling conductance and the ac conductance of a tunnelable MOS capacitor enables the determination of surface states distributions in semiconductors. Carrying out the measurement on hydrogenated amorphous silicon a-Si:H has revealed a non-uniform states distribution with a peak at about 0.45 eV below the conduction band edge. If the detected states are considered bulk states they appear to have a density of 10¹⁸ - 5×l0¹⁸ cm^-3 eV^-1 at this peak. The agreement between the above results and states distributions obtained on a-Si:H alloys from other methods, and on materials prepared in various deposition systems, indicates that this peak is a universal property of these alloys. The latter conclusion is shown to be applicable for the determination of the doping efficiency in the alloys.