Large deep-ultraviolet photocurrent in metal-semiconductor-metal structures fabricated on as-grown boron-doped diamond

Metal-semiconductor-metal planar devices have been fabricated on as-grown boron-doped homoepitaxial diamond thin films. They consist of two Schottky barriers connected back to back. The metal employed was a thin titanium (Ti) layer (5 nm) followed by a gold (Au) cap layer (50 nm), respectively. The structure shows a high ultraviolet photocurrent at 220 nm, which is seven orders of magnitude higher than the reverse dark current (< 1 pA) for at least an applied voltage of +/- 0.4 V. In addition, anomalous photoconductivity gain is observed. A plausible explanation could be the modification of the Schottky barrier under band-to-band illumination. The spectral photoresponse displays over six orders of magnitude discrimination between deep-ultraviolet (210 nm) and visible light (630 nm), and reveals a shoulder with an onset at 4.6 eV.