THROUGH-WAFER OPTICAL COMMUNICATION USING MONOLITHIC INGAAS-ON-SI LEDS AND MONOLITHIC PTSI-SI SCHOTTKY-BARRIER DETECTORS

Through-wafer optical communication has been demonstrated in experiments employing two vertically stacked Si wafers, the upper one with In0.15Ga0.85As-In0.15Al0.85As double-heterostructure LED's grown by molecular beam epitaxy on its top surface and the lower one with PtSi-Si Schottky-barrier detectors fabricated on its bottom surface. Infrared radiation emitted by the LED's in a band peaking at 1.12-mu-m, just beyond the Si absorption edge, is transmitted through the upper Si wafer, focused with a 25-mm focal-length lens, transmitted through the lower Si wafer, and detected by the Pt-Si detectors. For a single LED-detector pair, the detector signal-to-noise ratio was 10:1 for an LED drive current of 1 mA at room temperature. This observation, together with initial results on LED reliability, signal modulation, and array uniformity, suggests that through-wafer communication using LED's and Schottky-barrier detectors is a promising approach for optical interconnects in stacked wafer architectures. Such three-dimensional architectures are significant for both conventional and neuromorphic computing systems.