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.