Progress in quantum well and quantum cascade infrared photodetectors in SITP

This paper presents a review of recent advances in quantum well and quantum cascade infrared photodetectors developed in Shanghai Institute of Technical Physics, Chinese Academy of Sciences (SITP/CAS). Firstly, the temperature- and bias-dependent photocurrent spectra of very long wavelength (VLW) GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) are studied using spectroscopic measurements and corresponding theoretical calculations in detail. We confirm that the first excited state, which belongs to the quasi-bound state, can be converted into a quasi-continuum state induced by bias and temperature. Aided by band structure calculations, we propose a model of the double excited states that determine the working mechanism in VLW QWIPs. Secondly, we present an overview of a VLW QWIP focal plane array (FPA) with 320 x 256 pixels based on the bound to quasi-bound (BTQB) design. The technology of the manufacturing FPA based on the QWIP structures has been demonstrated. At the operating temperature of 45 K, the detectivity of QWIP FPA is larger than 1.4 x 10(10) cm.Hz(1/2)/W with a cutoff wavelength larger than 16 mu m. Finally, to meet the needs of space applications, we proposed a new long wavelength quantum cascade detector with a broadband detection ranging from 7.6 mu m to 10.4 mu m. With a pair of identical coupled quantum wells separated by a thin barrier, acting as absorption regions, the relative linewidth (Delta E/E) of response can be dramatically broadened to 30.7%. It is shown that the spectral shape and linewidth can be tuned by the thickness of the thin barrier, while it is insensitive to the working temperature. The device can work above liquid nitrogen temperature with a peak responsivity of 63 mA/W and Johnson noise limited detectivity of 5.1 x 10(9) cm.Hz(1/2)/W.