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In this paper fundamental physical properties of two material systems, HgCdTe and T2SLs, are compared together with their influence on detector performance: dark current density, RA product, quantum efficiency, and noise equivalent different temperature. In comparison with HgCdTe, fundamental properties of T2SLs are inferior. On the other hand, T2SL and barrier detectors have several advantages to include lower tunnelling and surface leakage currents, and suppressed Auger recombination mechanism. Up to date, the promise of superior performance of these detectors has not been realized yet. In the paper we present that the performance of T2SL detectors (dark current, current responsivity, and noise equivalent difference temperature) is lower than bulk HgCdTe photodiodes.
Due to stronger, less ionic chemical bonding of III-V semiconductors, these materials are attractive due to manufacturability and stability. It is also predicted that the interband T2SL quantum cascade devices will outperform the performance of the high operating temperature HgCdTe detectors.
Short time constant (τs) is directly related to the unique carrier transport properties of the IB CID structures, where at 380 K ~ 4 ns τs was observed. What is more, thermal generation recombination rates of IB CIDs are orders of magnitude reduced in comparison with corresponding intersubband quantum cascade infrared detectors (IC QCID) giving flexibility in higher operating temperature (HOT) applications. The most important feature is that the multiple-stage architecture is useful for improving the sensitivity of HOT detectors, where the quantum efficiency is limited by short diffusion length. Assuming that absorption depth for IR radiation is longer than the diffusion length, only a limited portion of the photogenerated carriers contribute to the quantum efficiency. That could be circumvented by fabrication of multi-stage devices where each equal stage consist of active, relaxation and barrier layers. IB CID T2SLs InAs/GaSb detector operating at 380 K exhibits Johnson noise limited detectivity at the level of ~ 108 Jones without implementation of immersion lens.
In this paper the current status of novel HOT T2SLs InAs/GaSb IB CID is presented. Analysis of the detector’s performance versus bias voltage and operating temperatures and future trends in development of the quantum cascade detectors are shown. The paper focuses on development of IR HOT detectors and potential approaches related to materials - T2SLs InAs/GaSb where IB CIDs that eliminate the cooling requirements of IR photodetectors operating in MWIR range are presented. The prediction of near future impact of that technology on infrared detector development is also shown.
Based on these promising results it is obvious now that the InAs/GaSb superlattice technology is competing with HgCdTe third generation detector technology with the potential advantage of standard III-V technology to be more competitive in costs and as a consequence series production pricing. Comments to the statement whether the superlattice IR photodetectors can outperform the “bulk” narrow gap HgCdTe detectors is one of the most important questions for the future of IR photodetectors presented by Rogalski at the April 2006 SPIE meeting in Orlando, Florida, are more credible today and are presented in this paper. It concerns the trade-offs between two most competing IR material technologies: InAs/GaSb type-II superlattices and HgCdTe ternary alloy system.
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