Origin of surface electron accumulation and fermi level pinning in low energy ion induced InN/GaN heterostructure

Abstract

InN/GaN heterostructure was fabricated via reactive low energetic Nitrogen ion (LENI at 300 eV) bombardment at lower substrate temperature (350 °C). X-Ray Photoemission spectroscopic (XPS) and Atomic Force Microscopic (AFM) measurements were performed to analyse the electronic structure, surface chemistry, band alignment, and the morphology of the grown heterostructure. XPS analysis revealed the evolution of InN structure with nitridation time, surface electron accumulation, fermi level pinning and the band offset of the grown InN/GaN hetero structure. The valence band and conduction band offsets (VBO & CBO) were calculated to be 0.49 ± 0.19 eV and 2.21 ± 0.1 eV and divulged the formation of a type-I heterojunction. A Fermi Level (FL) pinning of 1.5 ± 0.1 eV above the conduction band minima was perceived and indicated towards strong downward band bending. The analysis of the VB spectra suggested that surface electron accumulation occurred due to the presence of metallic In-adlayer on the surface which resulted in FL pinning and the corresponding downward band bending. Atomic Force Microscopy analysis divulged the formation of smooth surface with granular structure. It was also observed that the growth parameters (e.g. substrate temperature) strongly influence the aforementioned surface and interfacial properties.