A NEW HIGH ULTRAVIOLET SENSITIVITY FTO-GAP SCHOTTKY PHOTODIODE FABRICATED BY SPRAY-PYROLYSIS

A new high quantum efficiency gallium phosphide Schottky photodiode ha s been developed by spray deposition of heavily doped tin oxide films on n-type epitaxial structures, as an alternative to the conventional Schottky photodiodes using a semitransparent gold electrode. It is sho wn that fluorine-doped tin oxide films are more effective as transpare nt electrodes than tin-doped indium oxide films. The proposed photodio des have a typical responsivity near 0.33 A W-1 at 440 nm and an unbia sed internal quantum efficiency close to 100%, in the range from 250 t o 450 nm. The model used to calculate the internal quantum efficiency (based on the optical constants of tin oxide films and gallium phosphi de epitaxial layers) is found to be in good agreement with the experim ental results. The data show that the quantum efficiency is strongly d ependent on the thickness of the transparent electrode, owing to optic al interference effects. The noise equivalent power for 440 nm is 2.7 x 10(-15) W Hz(-1/2), which indicates that these photodiodes can be us ed for accurate measurements in the short-wavelength range, even in th e presence of stronger infrared background radiation.