Effects of UV/O₃ and O₂ plasma surface treatments on the band-bending of ultrathin ALD-Al₂O₃ coated Ga-polar GaN

The recently demonstrated semiconductor grafting approach allows one to create an abrupt, low interface-trap-density heterojunction between a high-quality p-type single-crystalline semiconductor (non-nitrides) with n-type GaN. However, due to the surface band-bending from GaN polarization, an energy barrier exists at the grafted heterojunction, which can impact the vertical charge carrier transport. Reducing the energy barrier height is essential for some advanced device development. In this work, we employed UV/O₃ and O₂ plasma to treat a Ga-polar GaN surface with/without an ultrathin (∼2 nm) ALD-Al₂O₃ coating and studied the effects of the treatments on surface band-bending. Through XPS measurements, it was found that the treatments can suppress the upward band-bending of the Ga-polar GaN by 0.11-0.39 eV. The XPS results also showed that UV/O₃ treatment is an effective surface cleaning method with little surface modification, while O₂ plasma causes a strong oxidation process that occurs inside the top layer GaN.