Surface Micromachined Tunable Resonant Cavity Led Using Wafer Bonding

Surface micromachining and wafer bonding techniques have been integrated to fabricate a dual-use resonant cavity tunable LED/photodetector operating at 1.5 mu m. The device has a tuning range of 75 nm, and a spectral linewidth (FWHM) of 4 nm, with an extinction ratio of greater than 20 dB throughout the tuning range. The device has potential applications in WDM networks and optical interconnects due to the small physical size, beam profile, and wafer-scale fabrication and testing possibilities.A GaAs/AlAs distributed Bragg reflector (DBR) is integrated with an InGaAsP strain-compensated multiple quantum well gain medium using wafer bonding. The InGaAsP material with a central wavelength of 1.52 mu m is grown lattice-matched on an InP substrate. After wafer bonding, the InP substrate is removed, leaving the active layers on the GaAs-based mirror and substrate.The top DBR mirror of the resonant cavity is formed using surface micromachining techniques. The mirror consists of a 4.5 pair Si/SiO2 DBR and a Ti/W support and contact layer. These materials are deposited on a sacrificial polyimide layer above the InP-based gain medium. The polyimide is selectively etched to release the membrane, creating an air gap between the top mirror and the epitaxial layers. When a voltage is applied between these two layers, the membrane is deflected towards the substrate, changing the Fabry-Perot cavity length, and causing a corresponding change in the resonance wavelength of the device.The device functions as a resonant cavity photodetector by reverse biasing the multiple quantun well (MQW) region. The absorption bandwidth and wavelength tuning are identical to the emission characteristics of the same device when used as an LED.