Monolithic Multichannel Ultraviolet Photodiodes Based on (Mg,Zn)O Thin Films With Continuous Composition Spreads

Abstract

We report on the fabrication of monolithic multichannel metal-semiconductor-metal photodiode arrays based on ternary (Mg,Zn)O thin films in wurtzite modification. The narrow bandwidth and the wavelength-selectivity of the device operating in visible-blind spectral range have been realized by employing a novel continuous composition spread approach relying on a single segmented target of pulsed-laser deposition. The Mg-content and subsequently the bandgap of thin films vary linearly along the compositional gradient across the wafer allowing the tuning of cutoff energies of the photodiode. In our device, the Mg-composition gradient of the active and optical filter layer (resulting in the narrow bandwidth of the photodiode) are designedly deposited with an angle of 72 ° with respect to each other. Here the onset of absorption is tuned over 430 meV and the bandwidth of the photodiodes is controlled from 270 meV down to 29 meV.