III-V semiconductor quantum well and superlattice detectors

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Abstract
The paper reviews the development of IR detectors for the 8 - 12 micrometer wavelength range based on GaAs/AlGaAs quantum well structures and InAs/(GaIn)Sb short-period superlattices (SPSLs) at the Fraunhofer-Institute IAF. Photoconductive GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) are used for the fabrication of starring IR cameras for thermal imaging in the third atmospheric window. The long wavelength infrared (LWIR) camera, devleoped in cooperation with AEG Infrarot-Module (AIM), consists of a two-dimensional focal plane array (FPA) with 256 X 256 detector elements, flip- chip bonded to a read-out integrated circuit (ROIC). The technology for the fabrication of FPAs, electrical and optical properties of single detector elements in the two-dimensional arrangement and the properties of the LWIR camera system are reported. A noise equivalent temperature difference (NETD) below 10 mK has been measured at an operation temperature of T equals 65 K with an integration time of 20 ms. More than 99.8% of all pixels are working and no cluster defects are observed. InAs/(GaIn)Sb SPSLs with a broken gap type-II band alignment are well suited for the fabrication of IR detectors covering the 3 - 12 micrometer spectral range. Due to the lattice mismatch of the InAs/(GaIn)Sb SPSL with respect to GaSb, tight control of thickness and composition of the layers and a controlled formation of the chemical bonds across the interface in the SPSLs are used for strain compensation. Photodiodes with a cut-off wavelength (lambda) c equals 8 micrometer and a current responsivity R(lambda ) equals 2 A/W exhibit a dynamic impedance of R0A equals 1k(Omega) cm2 at T equals 77 K. This leads to a Johnson- noise limited detectivity in excess of D* equals 1 X 1012 cm(Hz)1/2/W for these type of detectors.

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