A Comparative Study of Metal-Semiconductor-Metal Photodetectors on GaAs with Indium-Tin-Oxide and Ti/Au Electrodes

Abstract

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 A = 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 μm 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. © 1992 IEEE