Room temperature, surface-emitting light-emitting diodes exceed 2-GH¥bandwidth

Room temperature, surface-emitting light-emitting diodes exceed 2-GH¥bandwidth

Researchers at the Interuniversity Microelectronics Center (IMEC; Leuven, Belgium) have demonstrated GaAs surface-emitting light-emitting diodes (LEDs) with bandwidths in excess of 2 GH¥and high external efficiencies. The LEDs, which operate at room temperature, are based on a resonant tunneling structure. The IMEC device gets around the quantum-efficiency reduction that plagues conventional LEDs designed for high-speed modulation by obviating the need for a heavily doped active layer. The fast response of a resonant-tunneling LED is provided by a fast quantum-well tunneling escape time. The LEDs are PIN diodes with a double-barrier resonant-tunneling structure. Simultaneous intraband tunneling of electrons and holes causes injection electroluminescence from the quantum well and from the accumulation layers on either side of the resonant-tunneling structure.

Previously reported resonant-tunneling designs were limited by a decrease in internal quantum efficiency that accompanied increases in the tunneling escape rate, and the devices had to be operated at cryogenic temperatures. The IMEC device is based on accumulation layer emission, however, so that switching speeds are governed by tunneling supply and escape of only one carrier. This configuration increases charge accumulation and provides a 0.21% electrical-to-optical power conversion efficiency at 2.2 GH¥at room temperature.