Morphology dependent surface properties of nanostructured GaN films grown by molecular beam epitaxy

TL;DR

This study investigates how the surface properties and band structure of GaN films vary with morphology, revealing that nanowall networks exhibit superior conductivity and unique electronic features compared to flatter films.

Contribution

It provides new insights into the relationship between morphology and surface chemistry, band structure, and defect properties of GaN films grown by molecular beam epitaxy.

Findings

Nanowall networks show highest conductivity and no defect luminescence.

Flatter films are more resistive and exhibit yellow luminescence due to Ga vacancies.

GaN nanowalls have a Fermi level pinning at 1.8 eV above the valence band.

Abstract

The effect of film morphology on its surface chemistry and band structure has been analyzed for gallium nitride epitaxial films grown by molecular beam epitaxy. The film morphology has been studied using scanning electron microscopy and atomic force microscopy, and the bandstructure, defect and emission properties have been studied by X ray photoelectron spectroscopy and cathodoluminescence spectroscopy. It was found that the highly porous GaN nanowall network shows the highest relative conductivity and does not have defect related luminescence. The flatter films were more resistive and showed yellow luminescence, due to Ga vacancies. GaN nanowall network exhibited a Fermi level pinning at (1.8 $\pm$ 0.2) eV above valence band maximum, suggesting the presence of a Ga adlayer on the surface of GaN nanowall network. Ar ion sputtering was found to preferentially sputter N atoms leading to surface metallization.