GaN-Based Nanorods/Graphene Heterostructures for Optoelectronic Applications

The insulating character of sapphire, meltback etching of Si, bulk and surface defects prevented the efficient integration of GaN nanostructures in optoelectronic devices. Here, it is demonstrated that graphene can simultaneously serve as an electrical bottom contact, a chemically inert buffer layer, and a superior lattice and thermal matched growth substrate. Vertically aligned, high crystal quality GaN nanorods (NRs) without bulk defects such as threading dislocations and with only a mild strain at the NRs' base are grown by metal-organic vapor-phase epitaxy on defect-free graphene using nanometer-sized AlxGa1-xN nucleation islands. Here no influence of the supporting substrate on the GaN epitaxy is observed. However, at defects in graphene the effects of dangling bonds and the underlying substrate, presumably through nanoholes in graphene, on the properties of GaN NRs are visible. It is also shown that surface defects in InxGa1-xN/GaN NRs from planar films produced by etching of the defective material can be effectively passivated with only 10 nm alumina deposited by atomic layer deposition. This is confirmed by the increase in electroluminescence measured on finished devices with graphene top contact. These results can potentially lead to new material combinations including graphene, GaN, and other relevant semiconductors like Si toward yet unexplored device concepts.