Contact resistance to undoped and phosphorus-doped hydrogenated amorphous silicon films

An extensive systematic study of contact properties to as-deposited undoped and phosphorus-doped hydrogenated amorphous silicon (a-Si) in metal/a-Si diode configuration has shown that the magnitude of the contact resistance can be adjusted to some degree by the proper choice of metal work function. It is also obvious from our experimental data that the film doping (or bulk resistivity) is the most important factor in controlling the value of contact resistance for a given metallization. The lowest contact resistance values for both undoped and doped films have been achieved for Eu, Y, Sc, and Mg. Reasonable values for heavily doped films have also been obtained for Ti, Ta, Mo, and Al contacts. We have also shown, for the first time, that a further decrease of contact resistance can be achieved by increasing the doping efficiency of the phosphorus-doped layer.