High-speed gallium arsenide light emitting diodes
Abstract
For the realization of a cost-effective optical transmission system, a reliable low-cost visible light source is required which is capable of sufficiently high transmission rates. In the past, optical data links rely on both semiconductor light-emitting diodes (LEDs) and diode lasers. For short-distance, moderate-speed interconnects for use in a desk-top local area network, home network and gigabit Ethernet, LEDs are interesting alternative due to the simplicity of the device structure, ease of fabrication, high reliability and direct logic drive. All the above translates into cost savings on the system level. In this project, we developed infrared 890 nm LEDs operating at 1.7 GHz with internal quantum efficiencies of 10%. By carefully controlling the parameters of a molecular beam epitaxy growth process, we can greatly increase the doping density of the LED's GaAs active region without introducing non-radiative lifetime mechanisms. This process allows shorter radiative lifetimes and thus higher modulation frequencies while maintaining high efficiencies. With a factor of six improvement on optical output efficiency than the previous work on GHz bandwidth LEDs, a 2.5μW/mA responsivity was obtained for LEDs with 1.7 GHz 3-dB cut-off. Devices grown with various growth conditions were made to investigate the effects of different growth parameters. Internal quantum efficiency as high as 80% was achieved for devices with lower doping density. Reliability tests were performed to investigate the failure mechanisms. Small-signal modulation response gives the 3-dB cut-off of these LEDs as high as 1.7 GHz. To check the compatibility in a digital data link system application, large signal high-speed modulation characteristics including eye diagrams and bit error rates (BER) at high data rates and various light output powers were performed. Open eye patterns were seen and BER < 10−9 were obtained at data rates exceed 1 Gbps demonstrating the Gbps capability of these LEDs in a digital data link.
Degree
Ph.D.
Advisors
Woodall, Purdue University.
Subject Area
Electrical engineering
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