Higher-efficiency Si LED's with standard CMOS technology

Multi-junction silicon light emitting devices (Si LED's) were designed and realised by using standard 1.2 micron and 2 micron CMOS processes with a bipolar capability and with no modifications to the processes. The designs were optimised to increase the power conversion efficiency, quantum conversion efficiency, intensity of emission and also the uniformity of emission. The devices emit light of several nW per 5 to 10 mA at 4-30 V in the 450 to 850 nm wavelength range. All the devices operated with at least one pn junction in the field emission or avalanche breakdown mode. Quantum conversion efficiencies of up to 1/spl times/10/sup -5/ have been measured which is two and a half orders to three orders of magnitude higher than previously published values for light emission from Si p-n avalanching junctions. Some directional light emission characteristics were also observed. The developed devices are viable for on-chip electro-optical applications and also for high speed chip-to-environment electro-optical applications.