Indium Tin Oxide - Gallium Arsenide Photodiodes for Operation at Frequencies Beyond 110GHz

An Indium Tin Oxide/GaAs photodiode has been demonstrated with -3dB bandwidths in excess of 110 GHz (~4 ps FWHM). This device exhibits an external quantum efficiency of ≫25% (~0.2A/W) at 820 nm and is fundamentally limited by the active layer thickness. The device has been mounted such that direct measurements of bandwidth could be made using external mixers and a high-frequency spectrum analyser. The bandwidth agrees well with the Fourier transform of a theoretically predicted pulse duration of 4.2 ps FWHM. Corroborative data obtained using the optoelectronic cross-correlation technique are also presented.