High power mid-wave and long-wave infrared light emitting diodes: device growth and applications

Abstract

High brightness light emitting diodes based on the InAs/GaSb superlattice material system have been developed for use in mid-wave and long-wave infrared optoelectronic systems. By employing a multiple active region device configuration, high optical output has been demonstrated from devices in the 3-5μm and 7-12μm spectral bands. Mid-wave infrared optical output in excess of 0.95mW/sr has been observed from 120×120μm2 devices with peak emission at 3.8μm, and nearly 160μW/sr has been measured from devices of the same size operating at 8μm. Larger devices (1×1mm^2) with output as high as 8.5mW/sr and 1.6mW/sr have been demonstrated with mid-wave and long-wave devices, respectively, under quasi-DC bias conditions. The high switching speed inherent to small area light emitting diodes as well as potentially high optical output make these devices appealing candidates to improve upon the current state-of-the-art in infrared projection technology. Simulation of thermal scenes with wide dynamic range and high frame rates is desirable for calibration of infrared detection systems. Suitable projectors eliminate the need for observation of a live scene for detector calibration, thereby reducing costs and increasing safety. Current technology supports apparent temperature generation of up to approximately 800 Kelvin with frame rates of hundreds of frames per second; strong desire exists to break these barriers. Meeting the requirements of the aforementioned application requires development of the InAs/GaSb superlattice material system on multiple levels. Suppressing parasitic recombination channels via band structure engineering, improving carrier transport between active regions and confinement within active regions, reduction of defect-assisted recombination by optimizing device growth, and improving device fabrication and packaging are all routes requiring exploration. This work focuses on the latter two components of the optimization process, with emphasis on molecular beam epitaxial growth of high quality devices. Particular attention was paid to tailoring devices for thermal imaging applications and the design tradeoffs and limitations which impact that technology. Device performance and optimization success were gauged by electronic, optical, morphological, and structural characterization.