Ultraviolet photovoltaic characteristic of MgB2 thin film

Ultraviolet photovoltaic characteristic of MgB2 thin film

Fast photoelectric effects have been observed in MgB₂ thin film fabricated by chemical vapour deposition. The rise time was $\sim $10 ns and the full width at half-maximum was \sim185\,ns for the photovoltaic pulse when the film was irradiated by a 308\,nm laser pulse of 25\,ns in duration. X-ray diffraction and the scanning electron microscope revealed that the film was polycrystalline with preferred c-axis orientation. We propose that nonequilibrium electron--hole pairs are excited in the grains and grain boundary regions for MgB₂ film under ultraviolet laser and then the built-in electric field near the grain boundaries separates carriers, which lead to the appearance of an instant photovoltage.