Data_Dopant free method for ohmic metal-semiconductor contact formation utilizing charged dielectrics

Ohmic metal-semiconductor contacts are conventionally achieved by externally doping the surface of a semiconductor before metallization. To avoid the inconveniences that come with the heavy doping, we propose an alternative way of achieving an ohmic metal-semiconductor contact. The idea is to utilize a highly charged insulating thin film, which attracts charge carriers of opposite polarity from the substrate towards the surface, mimicking the addition of external dopants. The resulting accumulation/inversion layer should narrow the Schottky barrier under the metal consequently forming an ohmic contact. Here we select atomic layer deposited (ALD) Al2O3, known to have high negative charge, as the insulating thin film, Al as the metal, and Si as the semiconductor, and fabricated Al/p+ Si contacts to test the idea. We characterize the resulting contact properties by I-V measurements and the transfer length method. The results show that the Al2O3 induced Al/p+ Si contacts are not only ohmic, but also have a low contact resistivity of around 0.13 mΩcm2. This matches the requirements of various electron devices such as photodiodes demonstrating the potential of the proposed contact formation method.