HIGH QUANTUM EFFICIENCY PHOTOCATHODES FOR DETECTION OF 1.06 MICROMETER RADIATION

LOW-NOISE PHOTOCATHODES ABLE TO DETECT 1.06 MICROMETER - WAVELENGTH RADIATION WITH REASONABLE EFFICIENCY ARE NEEDED FOR SPACEBORN LIDAR SENSOR SYSTEMS UTILIZING ND:YAG LASERS. PHOTOCATHODES WITH 1.06 MICROMETER QUANTUM EFFICIENCIES EXCEEDING 1% HAVE BEEN FABRICATED IN THE PAST BUT ARE NOT COMMERCIALLY AVAILABLE AT PRESENT. SPIRE PROPOSES TO DEVELOP NEGATIVE-ELECTRON-AFFINITY PHOTOCATHODES BASED ON THE USE OF GAINAS ACTIVE LAYERS. WHILE MANY III-V MATERIALS HAVE THE PROPER BANDGAP TO DETECT 1.06 MICROMETER RADIATION, GAINAS HAS ADVANTAGES SUCH AS A PROVEN ABILITY TO DEMONSTRATE HIGH QUANTUM EFFICIENCY AND LONG DIFFUSION LENGTHS IN OTHER APPLICATIONS AND A SIMPLICITY OF DEPOSITION CONTROL NOT FOUND IN THE QUATENARY COMPOUNDS. THE EPITAXIAL STRUCTURE WILL BE GROWN BY METALORGANIC CHEMICAL VAPOR DEPOSITION ON A GAAS SUBSTRATE. PHASE I RESEARCH WILL SEEK TO DEMONSTRATE THE FEASIBILITY OF GROWING GAINAS LAYERS WHICH POSSESS OPTOELECTRONIC PROPERTIES SUITABLE TO THE FABRICATION OF EFFICIENT 1.06 MICROMETER PHOTOCATHODES. FURTHER OPTIMIZATION OF THIS MATERIAL AND THE FABRICATION AND TESTING OF COMPLETE PHOTOCATHODES DEVICES WILL BE THE SUBJECT OF PHASE II.