4H-SiC junction photodiodes, obtained by aluminium (Al) ion-implantation on low doped n-type epilayers are widely characterized observing an extremely low dark current density< 1 nA/cm2 at-100 V up to 90 C, a peak responsivity of 0.11 A/W at 280 nm corresponding to a quantum efficiency of 50% and a visible blindness> 10 3. The absence of optically active defects and pairs recombination centers was monitored by electro-optical and Emission Microscopy measurements.