Highly sensitive photo-detectors for the ultra-violet wavelength range based on a dielectric stack and a silicon on insulator substrate

Abstract

We propose and demonstrate planar metal-insulator-semiconductor-metal photodetectors fabricated on a silicon-on-insulator substrate with an n-type silicon device layer. The gate insulator comprises a double layer dielectric stack of SiO2 and HfO2. Detectors with different electrode geometries were characterized in a wide wavelength range: from 245 nm to 880 nm. A responsivity of 1.77 A/W was achieved at 405 nm independent of the illumination intensity, while at 245 nm, the responsivity was found to be nonlinear and at an intensity of 8 μW/cm2, it reached a record value of 30.5 A/W. Local fringing electric fields across asymmetric metal-insulator-semiconductor and metal-semiconductor junctions, stemming from the insulator stack and a reduction of the effective barrier height under illumination, are assumed to cause the high responsivity at wavelengths longer than 365 nm. The super linear rise in responsivity for wavelengths shorter than 285 nm is due to deep trap states which are charged by the injected electrons.