ABSTRACTAnnealing effects on the Al/a-Si:H structure in the temperature range 100°C to 300°C have been studied. Aluminum was evaporated on device quality phosphorous doped n+ a-Si:H films deposited in a UHV-PECVD system. The transmission line model (TLM) technique was used to measure the sheet resistance and contact resistivity of the films. For samples where Al covered the entire a-Si:H surface during annealing, sheet resistance and contact resistivity were found to decrease monotonically with annealing temperature. On the other hand, samples annealed after patterning Al pads showed a minimum in sheet resistance and contact resistivity at temperatures between 170°C and 200°C with a steep increase beyond 250°C. Optical and scanning electron microscopy, as well as surface profilometry, were used to study the surface morphology. A simple model involving Al interaction with the a-Si:H at the surface is proposed to explain the electrical behavior.