AlGaN-Based Linear Array for UV Solar-Blind Imaging From 240 to 280 nm

The realization of a linear array of 300 pixels, with a 26-mum pitch, based on Al
_x
Ga
_1-x
N metal-semiconductor-metal photodetectors, is described. The composition of the active layer is chosen in order to optimize the solar-blind operation: A sharp cutoff at 280 nm is observed, with discrimination between far and medium ultraviolet (UV) of three orders of magnitude. The detector shows a peak responsivity of 12 mA/W and a dark current smaller than 1 fA at the typical polarization of 4 V. The maximum resolution is analyzed in terms of modulation transfer function (MTF): The best result is obtained for a front-side illumination, i.e., when an MTF of 0.45 is measured at the half Nyquist frequency (19.2 lp/mm). Some UV images, which are obtained in a pushbroom model, are reported. The visible rejection is proven by directly imaging the arc of a Xenon lamp: It is shown that only the relatively weak far-UV component contributes to the signal