Band alignment and Schottky behaviour of InN/GaN heterostructure grown by low-temperature low-energy nitrogen ion bombardment

InN/GaN heterostructure based Schottky diodes are fabricated by reactive Low Energy Nitrogen Ion (LENI) bombardment at low substrate temperature (300 degrees C). The valence band offset (VBO) of the nitrogen ion induced In-polar InN/GaN hetero-interface has been analyzed by X-ray photoelectron spectroscopy and it is determined to be 0.72 +/- 0.28 eV, a type-I straddled band alignment is formed at the InN/GaN interface. Fermi level pinning is observed to be 1.3 +/- 0.1 eV above the conduction band minimum resulting in a strong downward band bending. Valence band maxima of InN/GaN show that the surface electron accumulation occurs due to the presence of In adlayer on the film. Atomic force microscopy analysis divulged the formation of a step like InN structure on the GaN surface. I-V characteristic showed that the junction between InN and GaN exhibits a Schottky type behaviour. The room temperature barrier height and the ideality factor of the InN/GaN Schottky diodes are calculated by using the thermionic emission (TE) model and found to be 0.72 eV and 20.8 respectivel

Electronic structure analysis of GaN films grown on r- and a-plane sapphire

The electronic structure and surface properties of epitaxial GaN films grown on r- and a-plane sapphire substrates were probed via spectroscopic and microscopic measurements. X-ray photoemission spectroscopic (XPS) measurements were performed to analyse the surface chemistry, band bending and valence band hybridization states. It was observed that GaN/a-sapphire display a downward band bending of 0.5 eV and possess higher amount of surface oxide compared to GaN/r-sapphire. The valence band (VB) investigation revealed that the hybridization corresponds to the interactions of Ga 4s and Ga 4p orbitals with N 2p orbital, and result in N2p-Ga4p, N2p-Ga4s*, mixed and N2p-Ga4s states. The energy band structure and electronic properties were measured via ultraviolet photoemission spectroscopic (UPS) experiments. The band structure analysis and electronic properties calculations divulged that the electron affinity and ionization energy of GaN/a-sapphire were 0.3 eV higher than GaN/r-sapphire film. Atomic Force Microscopic (AFM) measurements revealed faceted morphology of GaN/r-sapphire while a smooth pitted surface was observed for GaN/a-sapphire film, which is closely related to surface oxide coverage

A Comparative Photoelectron Spectroscopic Analysis of MBE and MOCVD Grown Epitaxial GaN Films

The report presents X-Ray Photoelectron Spectroscopic analysis of as-received and cleaned MBE and MOCVD grown undoped epitaxial GaN films. We correlate observed changes in electronic structure and surface properties after employing a newly derived approach to clean GaN surfaces. The adopted approach is a combination of two different standard cleaning procedures consisting of ex-situ wet chemical (HCl) etching followed by an in-situ ultrahigh vacuum anneal (up to 750 °C), and successfully yielded a clean and stoichiometric GaN surface. The method was employed to investigate cleanliness of MBE and MOCVD grown GaN films and it was observed that major contaminants such as carbon and oxygen were significantly removed from the surface. XPS analysis revealed that MBE grown films show higher amount of surface contamination than the MOCVD grown films but can also be cleaned more efficiently. Thermal annealing (≥ 750 °C) resulted in the dissociation of GaN bonds and accumulation of metallic gallium on the surface on MOCVD grown GaN films, which was confirmed by core level as well as the valence band spectra. The n O/n N ratio of the films reduced drastically from 1.79 to 0.04 and 0.73 to 0.09 after cleaning with the stoichiometry (N:Ga) of 1.0 ± 0.04 and 1.1 ± 0.05 for MBE and MOCVD grown GaN films respectively. The VB maximum position of MBE and MOCVD grown films was observed to be shifted from 2.9 ± 0 eV to 2.2 ± 0.1 eV and 2.8 ± 0.1 eV to 1.4 ± 0.1 eV after cleaning of the surface