SBIR-STTR Award

This proposal concerns the utilization of recently developed erbium-doped GaAs (GaAs:Er) containing ErAs quantum dots at approximately 2% volumetric concentration. Such GaAs:Er displays optimal THz performance because of excellent optical and electron-transport properties for driving at room temperature with 1550-nm lasers. The absorption coefficient at 1550 nm is > 5000 cm-1, the electron mobility is > 2000 cm2/V-s, and the dark resistivity is > 105 ohm-cm. The proposed Baseline Phase-I effort will commence with studying the uniformity and reliability of the electron and THz behavior in test devices at the (3.0-inch) wafer scale. It will then improve the performence even further using thicker epitaxial layers (2.0 compared to 1.0 um) and silicon nitride antireflection coating to improve the external quantum efficiency, and a better antenna (twin-slot) to improve the impedance matching to the THz device and therefore the available power for radiation into free space. Finally, the Optional Phase-I effort will focus on the 1550-nm optical-fiber coupling using industry-standard pigtailing techniques to allow arrays of such devices to be driven more efficiently and packaged more robustly, than what has been done in the past.

In our Phase I effort, we discovered that an ErAs quantum-dot array in a GaAs matrix under 1550 nm pulsed excitation produces cooperative spontaneous emission—Dicke superradiance—in the terahertz frequency region at room temperature. The broadband average terahertz power output can reach the level greater than 100 uW. In this proposal, our goal is to extend the quasi-sinusoidal character of the superradiance toward a CW source. This will be a two-faceted effort starting with representative Maxwell-Bloch semi-classical model of superradiance, and its Sine-Gordon governing equation. The second facet will be growth and fabrication of new superradiant structures integrated with optical cavities, followed by experimental confirmation using time-domain and calibrated frequency-domain experiments.