Enhanced performance of a GaN piezoelectric nanogenerator with an embedded nanoporous layer via the suppressed carrier screening effect

Highly efficient nanoporous GaN-based piezoelectric nanogenerators (PNGs) were demonstrated using an electrochemical etching process. The output of the PNGs was enhanced significantly with increasing porosity because Fermi-level pinning depletes free carriers in nanoporous GaN with thin walls, which reduces the internal screening of piezoelectric charges by free carriers. With the average wall thickness below 30 nm, the output of the PNG increased significantly with decreasing wall thickness. It was attributed to the piezoelectric and mechanical size effects, i.e., enhanced piezoelectric polarization by increased piezoelectric coefficient and reduced elastic coefficient in a nano structure. The energy-harvesting capability of a PNG was sufficient for the operation of a microelectronic device when it was combined with a charging capacitor and rectifying circuit.