APPLICATION OF INDIUM-TIN-OXIDE WITH IMPROVED TRANSMITTANCE AT 1.3-MU-M FOR MSM PHOTODETECTORS

The optical transmittance of indium-tin-oxide (ITO) at a wavelength of 1.3 mu m has been improved by adding forming gas (H-2/N-2) to the Ar sputtering gas. It is shown that the presence of H-2 in the plasma dec reases the carrier concentration in ITO, and increases the optical tra nsmittance of a 320 nm-thick ITO film from 69.7% to 99.5%. The applica tion of the high transmittance ITO to the fabrication of metal-semicon ductor-metal (MSM) photodiodes on InAlAs/InGaAs heterostructures has r esulted in an improvement of responsivity from 0.6 A/W to 0.76 A/W. Th is is double the responsivity of 0.39 A/W obtained for Ti/Au detectors . A 3-dB bandwidth of 6 GHz was obtained for the high transparency ITO device with 3 mu m fingers and gaps and with an area of 50 x 50 mu m( 2).