Effects of Mg accumulation on chemical and electronic properties of Mg-doped p-type GaN surface

Chemical and electronic properties of Mg-doped p-GaN surfaces were systematically investigated by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The doping density of Mg ranged from 3×1019 to 9×1019 cm−3. The XPS and AES analyses revealed the accumulation of Mg for all the air-exposed and chemically treated p-GaN surfaces. The apparent density of Mg calculated from the XPS integrated intensity and the AES intensity was more than one order higher than the value in bulk determined by secondary ion mass spectroscopy. Mg accumulation as well as large amounts of oxides made up the disordered region on the p-GaN:Mg surfaces. Large surface band bending of 1.2–1.6 eV was found at the p-GaN surfaces even after treatment in KOH and NH4OH solutions, due to the existence of high-density surface states. It was found that electron cyclotron resonance assisted N2 -plasma treatment at 300 °C for 1 min is very effective in removing such surface disordered regions and reducing surface band bending.