Electrical and chemical characterization of the Schottky barrier formed between clean n-GaN (0001) surfaces and Pt, Au, and Ag

The band alignment at the SiO 2-GaN interface is important for passivation of high voltage devices and for gate insulator applications. X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy have been used to observe the interface electronic states as SiO 2 was deposited on clean GaN͑0001͒ surfaces. The substrates, grown by metallorganic chemical vapor deposition, were n-(1ϫ10 17) and p-type (2ϫ10 18) GaN on 6H-SiC͑0001͒ with an AlN͑0001͒ buffer layer. The GaN surfaces were atomically cleaned via an 860°C anneal in an NH 3 atmosphere. For the clean surfaces, n-type GaN showed upward band bending of 0.3Ϯ0.1 eV, while p-type GaN showed downward band bending of 1.3Ϯ0.1 eV. The electron affinity for n-and p-type GaN was measured to be 2.9Ϯ0.1 and 3.2Ϯ0.1 eV, respectively. To avoid oxidizing the GaN, layers of Si were deposited on the clean GaN surface via ultrahigh vacuum e-beam deposition, and the Si was oxidized at 300°C by a remote O 2 plasma. The substrates were annealed at 650°C for densification of the SiO 2 films. Surface analysis techniques were performed after each step in the process, and yielded a valence band offset of 2.0Ϯ0.2 eV and a conduction band offset of 3.6Ϯ0.2 eV for the GaN-SiO 2 interface for both p-and n-type samples. Interface dipoles of 1.8 and 1.5 eV were deduced for the GaN-SiO 2 interface for the n-and p-type surfaces, respectively.

Photoemission spectroscopy has been used to observe the interface electronic states as HfO 2 was deposited on clean n-type Ga-face GaN ͑0001͒ surfaces. The HfO 2 was formed by repeated deposition of several monolayers of Hf followed by remote plasma oxidation at 300°C, and a 650°C densification anneal. The 650°C anneal resulted in a 0.6 and 0.4 eV change in band bending and valence band offset, respectively. The final annealed GaN/HfO 2 interface exhibited a valence band offset of 0.3 eV and a conduction band offset of 2.1 eV. A 2.0 eV deviation was found from the electron affinity band offset model.

X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy were used to measure electronic states as Si3N4 was deposited on clean GaN (0001) surfaces. The n-type (2×1018) and p-type (1×1017) GaN surfaces were atomically cleaned in NH3 at 860 °C, and the n-and p-type surfaces showed upward band bending of ∼0.2±0.1 eV and downward band bending of 1.1±0.1 eV, respectively, both with an electron affinity of 3.1±0.1 eV. Layers of Si (∼0.2 nm) were deposited on the clean GaN and nitrided using an electron cyclotron resonance N2 plasma at 300 °C and subsequently annealed at 650 °C for densification into a Si3N4 film. Surface analysis was performed after each step in the process, and yielded a valence band offset of 0.5±0.1 eV. Both interfaces exhibited type II band alignment where the valence band maximum of GaN lies below that of the Si3N4 valence band. The conduction band offset was deduced to be 2.4±0.1 eV, and a change of the interface dipole of 1.1±0.1 eV was observed for Si3N4/GaN interface formation.

No abstract