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 MSMs is measured to be approximately 0.8 A/W, which is twice that of conventional Ti/Au MSMs under normal operational bias conditions at lambda =850 nm. This higher responsivity is attributed to the transparency of the ITO electrodes. ITO MSMs exhibited a linear optical response over a wider bias range than Ti/Au MSMs. Also, a higher breakdown voltage was measured for ITO MSMs. The bandwidths of ITO and Ti/Au MSMs 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 MSMs is due to the longer transit time of the carriers generated beneath the ITO electrodes.<
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