On-chip fabrication of well-aligned and contact-barrier-free GaN nanobridge devices with ultrahigh photocurrent responsivity

On-chip fabrication of well-aligned and contact-barrier-free GaN nanobridge devices (NB) with ultrahigh photocurrent responsivity was demonstrated. A commercial wafer with a 2.0∓0.5μm thick layer of highly n+-doped c-plane GaN on sapphire was used as the substrate for fabrication of the NB device and arrays of Ni/n+-GaN electrode posts were patterned on the insulating sapphire substrate through the photolithography, lift-off, and reactive-ion etching methods. Arrays of n+-GaN posts were also prepatterned to expose a sidewall of selected orientation and after Au catalyst sputtering, nanowires were grown by thermal chemical vapor deposition (CVD) under the conditions of 800-1050°C and 760 Torr using NH3 and Ga as source reagents. High Resolution Transmission Electron Microscopy (HRTEM) and selected area electron diffractometry (SAED) were used to characterize the microstructure and orientation relationship of the NBs.