Direct growth of tungsten disulfide on gallium nitride and the photovoltaic characteristics of the heterojunctions

Photovoltaic device construct with a 2D nanomaterial atop a 3D wide bandgap semiconductor enables van Hove singularity induced enhanced light absorption on the front surface in close proximity (few atoms above) to the depletion region. Here, thin layers of tungsten disulfide (WS₂) varying from mono to few layers were grown directly on both n-gallium nitride (GaN) and p-GaN via low pressure chemical vapor deposition. The conditions for WS₂ growth were optimized for a larger coverage of the GaN substrate. The WS₂ film was characterized using confocal Raman spectroscopy and x-ray photoelectron spectroscopy. Ultraviolet photoelectron spectroscopy measurement was conducted to elucidate the electronic band structures of WS₂ on top of GaN. Afterwards, WS₂/GaN heterojunction photovoltaic devices were fabricated. The current density–voltage (J–V) tests were conducted to illustrate the electrical performance. The device showed an open circuit voltage of 0.53 mV and a short circuit current density of 60 µA cm⁻², 85% higher than that of a WS₂/Si solar cell. An external quantum efficiency was measured to be near 60% for red and infrared, and above 50% in the violet region. (paper)