Novel high speed light emitting devices.

摘要

Novel devices that overcome the speed limiting characteristics of conventional light emitting diodes (LEDs) to achieve high speed while maintaining radiative efficiency have been designed, fabricated, and characterized. To date, diode lasers have been used exclusively as optical emitters in high bit-rate fiber optic links. LEDs have been limited to use in low speed fiber optic links due to their comparatively low modulation bandwidth. In the future, massively parallel short reach links will be required for chip-to-chip and optical back plane applications. These systems will require large numbers of robust, low cost optical devices and may not require the performance afforded by lasers—making high speed LEDs an attractive choice if the limitations of current devices can be overcome. This thesis describes a technique to increase the switching speed of a light emitting device through the spatial relocation of minority carrier charge. Novel devices have been designed that use this technique. In one device, lowering an electrically controlled confinement barrier allows carriers to escape the active layer faster than the recombination rate; improving the fall time. Two novel devices that improve both the rise and fall times by quickly transferring a minority carrier population between two layers with different emission properties were designed and built as well. Several heavily doped conventional LEDs were also characterized for comparison with the novel devices. Optical transitions ten times faster than would be expected from a conventional LED with a similar active layer composition were observed in the fastest novel device. The improvement in speed is made without sacrificing radiative efficiency in the active layer of the device.