UV Metal Semiconductor Metal Detectors. A Robust Choice for (Al,Ga)N Based Detectors

Abstract

UV detection is interesting for combustion optimization, air contamination control, fire and solar blind rocket launching detection. Most of these applications require that UV detectors have a huge dynamic response between UV and the visible, and a very low dark current in the range of the UV flux measured. (Al,Ga)N alloys present a large direct bandgap in this range and therefore can be used as an active region in such detectors. To take advantage of the large Schottky barrier, the good alloy quality, and to avoid any doping problems, we have developed MSM photodetectors. High quality material has been grown with MOCVD and MBE on sapphire substrates. Stress management is employed for aluminum contents up to 65% to reduce crack density. This is correlated with non-ideal features like dark current, sub-bandgap response and non-linearity between photocurrent and optical flux. The spectral selectivity between UV and visible reaches five orders of magnitude. A geometry of inter-digitized fingers is optimized in regards to the peak response. The Schottky barrier and a dielectric passivation result in dark currents lower than 1 fA up to 30 V for a 100 x 100 mum(2) pixel. Consequently, detectivity is mainly limited by shot noise and corresponds to a noise of 500 photons per second and per pixel.