Development and evaluation of a novel large-area single-pixel QWIP for infrared radiometry

Infrared radiometry requires large area, linear detectors of spatially uniform response. Currently the choice of high quality detectors of mid-infrared (>8 µm) radiation is far from ideal for radiometric applications. For example, HgCdTe detectors are widely used but exhibit very large (>20%) spatial non-uniformities in their responsivity whereas thermal detectors such as pyroelectric detectors have relatively low D* values. Quantum Well Infrared Photo-detectors (QWIPs) are now well established for use in state-of-the-art cooled thermal imaging systems, driven by military application. For fundamental optical measurement applications (for example, spectral responsivity standards) the expense and complication of imaging arrays is not required. Some QWIPs are made from layers of GaAs / AlxGa1-xAs material which can be mass grown on large substrate wafers with high spatial uniformity. As such, QWIPs offer the potential to be manufactured as a large area single pixel device, with a uniform spatial response, as well as a high D* value. This paper will detail the development of a single pixel QWIP detector and present the results of an initial evaluation of this detector, carried out at NPL.