High-performance LWIR InAs/InGaSb Superlattice Photodetectors

In this program, we propose to develop high-performance long-wavelength infrared (LWIR) photodetectors based on InAs/In(x)Ga(1-x)Sb Type II superlattice structures. The use of bandgap engineering approaches to control quantum confinement and strain effects allows for wide tunability of the superlattice bandgap, making these structures ideal for LWIR detection in the 8 to 12 um wavelength range. In Phase I of this program, we will grow and characterize at least three different epitaxial designs targeting a long wavelength cutoff of 8 um. With these structures, we aim to identify the most favorable design strategy for reducing bulk leakage current, with a focus on the reduction of Auger recombination. We will fabricate mesa-geometry devices to compare unpassivated, dielectric-passivated, and sulfur-passivated devices. We will also fabricate devices using a planar geometry that has proven extremely effective for more mature III-V photodetectors which entails dielectric thin film surface passivation followed by dielectric patterning and dopant diffusion to form planar p-n junctions. For both mesa and planar devices, detector geometries will be chosen with a wide variety of sizes and area-to-perimeter ratios to experimentally isolate bulk and perimeter leakage contributions. Dark current will be characterized over the temperature range from 77K to 300K and analyzed to determine the contributions of various leakage mechanisms. In the Phase I Option, we will characterize the optical properties of devices fabricated during the Phase I Base period as well as demonstrate reproducibility of the most promising growth and passivation approaches. This work will be extended in Phase II to InAs/In(x)Ga(1-x)Sb superlattice detectors with cutoff wavelengths of at least 12 um and the consequent development of focal plane arrays based on these detectors.