Monolithic integration of 1.3-mym InGaAs photodetectors and HEMT electronic circuits on GaAs

For the first time, monolithic optoelectronic receivers for a wavelength of 1.3 micrometer have been fabricated successfully on GaAs substrates using InGaAs metalsemiconductor-metal (MSM) photodiodes and AlGAs/GaAs/AlGaAs high-electron-mobility transistors (HEMTs). Using molecular beam epitaxy (MBE), the photodetector layers were grown on top of a double delta-doped AlGaAs/GaAs/AlGaAs HEMT structure which allows the fabrication of enhancement and depletion field effect transistors (FETs). The photoabsorbing InGaAs layer was grown at 500 deg. C. To fabricate the optoelectronic receivers, first, an etch process using a combination of non-selective wet etching and selective reactive ion etching (RIE) was applied to produce mesas for the photodetectors and to uncover the HEMT structure in all other areas. For the electronic circuits, our well-established HEMT process for 0.3-micrometer transistor gates was used which includes electron-bearn lithography for gate definition and optical litho graphy for NiCr thin film resistors, capacitors, and inductors. The interdigitated MSM photodiode fingers were also fabricated using electron-beam lithography. For interconnecting the electronic circuits and the photodetectors, air bridges were employed. The entire process was performed on 2-inch wafers with more than 90 percent yield of functional receivers. The finished receiver - basically an MSM photodetector linked to a transimpedance amplifier - is operational at an incident wavelength of 1.3 gm at data rates up to 1.2 Gbit/s. The sensitive of the detectors is 0.16A/W at a 10 V bias.