Electron beam lithography for the fabrication of nanopillars in type II indium arsenide/gallium antimonide superlattices for multicolor infrared focal plane arrays.

摘要

Presently, there exists an important need for high-performance infrared photodetectors and focal plane arrays operating in the 8-12 mum atmospheric transmission window. Civilian applications that may require these devices include law enforcement, medical imaging, satellite communications and deep space astronomy. Military uses include night vision, target designation and long-range missile detection.; Currently, HgCdTe is the material standard for detectors and focal plane arrays in the mid to long wavelength infrared. However, due to concerns such as growth nonuniformity and device yield, researchers at the Center for Quantum Devices at Northwestern University have investigated other material systems that may eventually replace HgCdTe, such as InAs/GaSb type II superlattices. Through optimization of growth techniques and material quality, the performance of these devices has become comparable to state of the art HgCdTe detectors.; This work describes the theoretical basis and motivation for nanostructures in type II InAs/GaSb materials as well as the fabrication of nanometer-scale type II superlattice structures for eventual use in multicolor infrared detector applications. Using electron beam lithography and reactive ion etching, significant fabrication advances are shown while patterning structures down to less than 20 nm diameter with 10:1 aspect ratios in the GaInAs, GaInP, GaSb and InAs/GaSb material systems. Photoluminescence experiments indicate the strong possibility of carrier confinement and quantum size effects. Furthermore, device fabrication steps for experimental testing of nanopillar characteristics have been developed and detailed. Electrical measurements have been performed temperatures down to 30 K. Finally, optical response from nanopillar devices in the GaInAs/InP QWIP material system has been demonstrated with detectivity of approximately 3x108 Jones at 30K and wavelength response of about 8.5 mum. This is the first demonstration of optical response from nanopillar arrays in this material system. Dark current and responsivity data has been fit to theoretical models in order to understand the physical phenomena that contribute to device performance. Prospects for future work in this field are also discussed.