Surface passivation of germanium nanowires using Al2O3 and HfO2 deposited via atomic layer deposition technique

We have successfully passivated the surface of germanium nanowires (Ge NWs) using aluminum oxide (Al2O3) and hafnium oxide (HfO2). The atomic layer deposition (ALD) technique was used to deposit Al2O3 and HfO2. We observed an excellent interface between the nanowire surface and Al2O3 and exceptional uniformity of Al2O3 along the length of the nanowire. In the case of nanowires coated with HfO2, we found that a local crystallization of HfO2 may cause defects on the nanowire surface. We have fabricated devices using Ge NWs coated with ultra-thin Al2O3. The current through the nanowire increased after sequential annealing at 400 degrees C under a forming gas atmosphere. The current increase is ascribed to the diffusion of germanium into Al2O3 that affects the barrier thickness between the metal and the Al2O3/Ge NW. The ultra-thin Al2O3 serves to eliminate charge trapping and protect the germanium surface from ambient molecules and therefore alleviate hysteresis. (C) 2014 The Japan Society of Applied Physics