Surface passivation of germanium nanowires using Al2O3and HfO2deposited via atomic layer deposition technique

We have successfully passivated the surface of germanium nanowires (Ge NWs) using aluminum oxide (Al 2 O 3 ) and hafnium oxide (HfO 2 ). The atomic layer deposition (ALD) technique was used to deposit Al 2 O 3 and HfO 2 . We observed an excellent interface between the nanowire surface and Al 2 O 3 and exceptional uniformity of Al 2 O 3 along the length of the nanowire. In the case of nanowires coated with HfO 2 , we found that a local crystallization of HfO 2 may cause defects on the nanowire surface. We have fabricated devices using Ge NWs coated with ultra-thin Al 2 O 3 . The current through the nanowire increased after sequential annealing at 400 °C under a forming gas atmosphere. The current increase is ascribed to the diffusion of germanium into Al 2 O 3 that affects the barrier thickness between the metal and the Al 2 O 3 /Ge NW. The ultra-thin Al 2 O 3 serves to eliminate charge trapping and protect the germanium surface from ambient molecules and therefore alleviate hysteresis.