Epitaxial TiN/GaN Heterostructure for Efficient Photonic Energy Harvesting

Plasmon-mediated hot carrier injection using the metal–semiconductor Schottky diode structure has been proposed for optical sensing and solar energy harvesting. But the low conversion efficiency and limited spectral range are the current concerns. Wide-bandgap (3.4 eV) gallium nitride (GaN) has been considered as an excellent semiconductor material for broadband conversion of photonic energy, but the achievable efficiency is still rather low. Here, we demonstrate an efficient hot-hole injection mechanism based on the photoconductive titanium nitride (TiN)/p-type GaN (p-GaN) metal–semiconductor heterostructure grown by molecular-beam epitaxy. Compared with the same device structure using a TiN/n-GaN heterojunction, the photocurrent conversion efficiency is increased 4 orders of magnitude. Moreover, an internal photovoltage, generated by interfacial charge transfer/separation across the TiN/p-GaN Schottky barrier (1.2 eV), enables a self-sustainable photocurrent without external biasing. For practical applications, the refractory material properties and broadband conversion (365–1033 nm) make this heterostructure system capable of harvesting highly concentrated solar light.