Surface Preparation of Gallium Nitride for Atomic Layer Deposition of Aluminum Oxide

Surface cleaning of gallium nitride (GaN) prior to atomic layer deposition (ALD) of aluminum oxide was investigated at both the atomic as well as device level. Two studies were performed, one in which an ALD process was developed and a second which explored the atomic level origins of defects in the Al₂O₃/GaN system. An ALD process was developed such that a high quality aluminum oxide gate dielectric could be deposited on GaN with only the use of an in-situ TMA pretreatment. This process was developed using a flow type reactor which allowed for the elimination of a hydrogen plasma surface treatment. In the second study, density functional theory modeling was used to examine the likely sources of defects in the Al₂O₃Al2O3 /GaN(0001) system. The modeling revealed that Al₂O₃ is able to passivate the majority of defect states on the GaN(0001) surface, but nucleation of oxide in every unit cell would be required to completely eliminate them. The use of a two-step surface treatment involving a wet clean in HCl and NH₄OH to remove native oxide followed by an in- situ dry clean using hydrogen and TMA was shown to improve the nucleation density. Calculated Dit values were reduced by a factor of 2-3 while border trap densities were reduced a full order of magnitud