Quantum dot infrared photodetectors with highly tunable spectral response for an algorithm based spectrometer

We report on low strain quantum dot infrared photodetectors (QDIP) with 80 dot in a well (DWELL) stacks. These QDIPs have been grown with lattice matched Al0.1Ga0.9As barriers and GaAs wells allowing a large number of stacks to be grown leading to an increased absorption volume. The QDIPs show a strong spectral response that varies significantly with applied bias, with four distinct peak wavelengths ranging from 5.5 mu m to 10.0 mu m. The highly tunable nature of the intrinsic responses makes these QDIPs very attractive as multispectral imagers in the MWIR and LWIR regions. The spectral diversity of these QDIPs has been exploited using an algorithm to produce a highly versatile algorithmic spectrometer. The algorithm assigns a specific weighting factor to each of the intrinsic responses and then sums these weighted responses to achieve any desired spectral shape. Triangular narrowband filters have been synthesised in this way with full width at half maximums (FWHM) as narrow as 0.2 mu m. The QDIPs can be used to image objects in the MWIR and LWIR regions by measuring the photocurrent generated at each specific bias and summing them using the calculated weighting factors for every wavelength of interest. This technique has been successfully used to capture the radiated power from a blackbody source through IR filters with different centre wavelengths and bandwidths as a function of wavelength in the LWIR and MWIR regions.