Submicron modulation-doped field-effect transistor/metal–semiconductor–metal-based optoelectronic integrated circuit receiver fabricated by direct-write electron-beam lithography

An all direct-write electron-beam fabrication process has been developed for the fabrication of monolithic optoelectronic integrated circuits (OEICs). Various electron-beam resist technologies are investigated including image reversed AZ5214, PMMA/P[MMA−MAA] bilayer, and PMMA/P[MMA−MAA]/PMMA trilayer. A novel single-step air-bridge formation process utilizing selective development is described. These processes are demonstrated in the fabrication of a 0.85-μm sensitive OEIC receiver comprised of a metal–semiconductor–metal (MSM) detector integrated with a submicron GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistor based transimpedance amplifier. A 3-dB transimpedance bandwidth of 5.6 GHz and a transimpedance bandwidth product of 4.8 THz Ω are measured for the amplifier. Discrete high-resolution MSM photodetectors with finger/gap spacings ranging from 0.1 to 1.0 μm have been fabricated and characterized.