Charged thin film enables dopant free ohmic metal–semiconductor contact formation

Ohmic contacts are conventionally achieved by externally doping the surface of a semiconductor substrate underneath a metal contact. To avoid the inconveniences that come with heavy doping, we propose an alternative way of achieving an ohmic Al-Si contact utilizing a highly charged atomic layer deposited (ALD) Al₂O₃ thin film. The idea is to utilize the negative charge of ALD Al₂O₃ to attract holes towards the surface of the Si substrate and thereby induce a p+ region and consequently an Al/p+ Si contact. The results show that the Al₂O₃ induced contacts are not only ohmic, but also have a low contact resistivity of 0.24 mΩ⋅cm². This matches the requirements of various electron devices such as photodiodes indicating potential for the proposed contact formation method.