A COMPARATIVE-STUDY OF METAL-SEMICONDUCTOR METAL PHOTODETECTORS ON GAAS WITH INDIUM TIN OXIDE AND TI/AU ELECTRODES

Metal-semiconductor-metal (MSM) photodiodes with interdigitated indium-tin-oxide (ITO) electrodes have been fabricated on undoped GaAs using reactive-ion-etching in a methane plasma. The responsivity of ITO-MSM's is measured to be approximately 0.8 A / W, which is twice that of conventional Ti / Au-MSM's under normal operational bias conditions at lambda = 850 nm. This higher responsivity is attributed to the transparency of the ITO electrodes. ITO-MSM's exhibited a linear optical response over a wider bias range than Ti / Au-MSM's. Also, a higher breakdown voltage was measured for ITO-MSM's. The bandwidths of ITO and Ti / Au-MSM's fabricated on the same semiconductor layer with 1-mu-m fingers and spaces were measured to be 6 and 9 GHz, respectively. The slower response of the ITO-MSM's is due to the longer transit time of the carriers generated beneath the ITO electrodes.