Electrical characterization of GaN/ALN heterostructures grown by molecular beam epitaxy on silicon substrates

Abstract

In this paper, $n$-type gallium nitride thin films were grown on $p$-type and $n$-type silicon substrates by Molecular Beam Epitaxy technique, employing an aluminum nitride layer as an insulator buffer coating. The samples constitute primary semiconductor-insulator-semiconductor or SIS heterostructures, on which silver electrical contacts were deposited superficially by sputtering for electrical characterization purposes. The current intensity vs. voltage curves, charge carriers density, diffusion coefficient and mobility of charge carriers were determined in darkness conditions. Under AM1.5 homogenous illumination, the samples exhibited relatively large open-circuit voltage values, but low values for energy conversion efficiencies. Additionally, the dependency in photon energy of the open-circuit voltage was determined, in the range 1.77 eV to 4.13 eV, showing a minimum in the energy corresponding to the GaN energy band gap. Finally we discuss the prevailing charge transfer mechanism.