Photo detectors for multi-spectral sensing

Device concepts of quantum well, dot, and ring for multi-band photodetection are presented in this paper. Results on a preliminary GaAs-based npn-Quantum Well Infrared Photodetector (QWIP) show two combinations of wavelength bands which can be selected using the applied bias. An InP based npn-QWIP structure is proposed to eliminate the cross talk between the bands. As a separate approach, a three band architecture is proposed to obtain response in three bands by combining split-off, interband and intraband transitions which are all bias selectable. Furthermore, in this paper, a dual band Superlattice Quantum Dot Infrared Photodetector (SL-QDIP), providing bias-selectability of the response peaks, is demonstrated. The active region of this detector, consists of two quantum dot super-lattices (SL) which were separated by a graded barrier, enabling photocurrent generation in only one super-lattice for a given bias polarity. Two different response bands, one consisting of three peaks at 4.4, 7.4 and 11 µm, were observed up to 120 K for reverse and forward biases, respectively. Additionally, the intersubband transitions in InAs/GaAs quantum rings have been studied. Quantum ring based photoconductive detectors with multiple quantum ring layers in the active region exhibit dark currents of ∼10 −8 A/cm 2 at a bias of 2 V at 4.2 K. The rings have a single bound state and emission of photoexcited carriers gives rise to a spectral response peaking at 1.82 THz at 5.2 K. This detector exhibits a peak responsivity of 25 A/W and specific detectivity D* of 10 16 Jones under 1 V bias at 5.2 K. The detectivity at 10 K, is measured ∼3 × 10 15 Jones.