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/sub 2//N/sub 2/) to the Ar sputtering gas. It is shown that the presence of H/sub 2/ in the plasma decreases the carrier concentration in ITO and increases the optical transmittance of a 320 nm-thick ITO film from 69.7% to 99.5%. The application of the high transmittance ITO to the fabrication of metal-semiconductor-metal (MSM) photodiodes on InAlAs/InGaAs heterostructures has resulted in an improvement of responsivity from 0.6 A/W to 0.76 A/W. This 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 mu m*50 mu m.>