Effect of GaN surface treatment on Al2O3/n-GaN MOS capacitors.

The surface preparation for depositing Al₂O₃ for fabricating Au/Ni/Al₂O₃/n-GaN (0001) metal oxide semiconductor (MOS) capacitors was optimized as a step toward realization of high performance GaN MOSFETs. The GaN surface treatments studied included cleaning with piranha (H₂O₂:H₂SO₄=1:5), (NH₄)₂S, and 30% HF etches. By several metrics, the MOS capacitor with the piranha-etched GaN had the best characteristics. It had the lowest capacitance-voltage hysteresis, the smoothest Al₂O₃ surface as determined by atomic force microscopy (0.2nm surface roughness), the lowest carbon concentration (∼0.78%) at the Al₂O₃/n-GaN interface (from x-ray photoelectron spectroscopy), and the lowest oxide-trap charge (QT = 1.6×10¹¹cm^-2eV^-1). Its interface trap density (D_it=3.7×10¹²cm^-2eV^-1), as measured with photon-assisted capacitance-voltage method, was the lowest from conduction band-edge to midgap. [ABSTRACT FROM AUTHOR]