Current Transport in Nanoscale Heterojunctions

One-dimensional (1D) ZnO nanostructures attracted increasing interest in recent years due to their potential in different optoelectronic applications. A variety of different techniques have been used for the preparation of ZnO nanostructures. Among them the solution-based methods attract attention due to the low and the possibility of a large scale production. A nucleation layer is generally required for the solution-grown ZnO nanostructures on virtually any substrate. ZnO has a similar thermal expansion and a low lattice mismatch to GaN. Growth of ZnO nanostructures on GaN templates is therefore a convenient alternative to generally polycrystalline nucleation layers deposited from solutions or from vapour phase. Moreover, the lack of p-type ZnO emphasizes the importance of heterojunctions realized on these materials. One of the crucial problems in such heterojunction is create contact on the ZnO NRs. Classically to create contact three steps approach is used: at first the free space between the individual ZnO nanorods are filled with isolation layer, after it oxygen plasma is used to remove isolation layer from the top of the ZnO NRs and finally contact is deposited. In additional in the most cases GaN is covered with a ZnO seed layer which creates interface state. All the listed fabrication approaches strongly affect both electrical and optical properties of as grown ZnO NRs and current transport in such heterojunctions. In this work we studied electro physical properties of the single ZnO NRs/GaN heterojunction where ZnO NRs were contacted directly by using conductive AFM or by a nanoprobe in high vacuum chamber of scanning electron microscope. This work was supported by the Czech Science Foundation projects 17-00546S and 17-00355S.