The performance of charge-sensitive infrared phototransistors ( λ∼14.7 μ m ) is studied at temperatures of up to 30 K. The devices, with a 16×4 μ m 2 photoactive area, are fabricated in GaAs/AlGaAs double-quantum-well structure. An excellent specific detectivity D*=9.6×1014 cm Hz 1/2/ W is derived in a T range of up to T=23 K . Experimental results are theoretically studied based on WKB approximation, in which photogenerated holes in the floating gate (FG) are recombined with thermal emission or thermally assisted tunneling from the outside of FG through the barriers. The model well reproduces the experimental results, including the vanishing of photosignal at 30 K under 280 fW incident radiation. The model is used to predict a temperature-dependent specific detectivity D* in ideal devices free from 1/f noise.
"The maximum operating temperature is expected to be roughly proportional to the photon energy. Noting T ≈ 25 K for λ = 15 μm (hν = 84 meV) , the temperature is expected to range from T ≈ 50 K for λ = 8 μm (hν = 154 meV) to T ≈ 4 K for λ = 80 μm (hν = 15.4 meV). Owing to the simple device structure, CSIPs are promising for integration to large-scale arrays. "
[Show abstract][Hide abstract] ABSTRACT: Semiconductor quantum dot detectors as well as semiconductor charge-sensitive infrared phototransistors are described. They are the only detectors that can count single photons in the terahertz region at present. In terms of the noise equivalent power (NEP), the detectors realize experimental values on the order of 10<sup>-21</sup> W/Hz<sup>1/2</sup>, while theoretically expected values are even much lower, on the order of 10<sup>-24</sup> W/Hz<sup>1/2</sup>. These NEP values are by several orders of magnitude lower than any other state-of-the-art highly sensitive detectors. In addition to the outstanding sensitivity, the detectors are featured by strong advantage of huge current responsivity (10<sup>6</sup>-10<sup>10</sup> A/W ) and extremely large dynamic range of response (10<sup>6</sup>-10<sup>8</sup>). The mechanism of detection as well as application of the detectors is discussed.
IEEE Journal of Selected Topics in Quantum Electronics 03/2011; 17(1-17):54 - 66. DOI:10.1109/JSTQE.2010.2048893 · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A scanning confocal long-wavelength infrared (LWIR) microscope has been developed by using a highly-sensitive, novel LWIR detector (charge-sensitive infrared phototransistor) for wavelengths -14.7 mum. Samples and Ge objective lens are placed at room temperature, while other optics including a confocal pinhole, Ge relay lenses, and the detector are cooled down to 4.2 K. Passive LWIR imaging has been achieved with a spatial resolution of 25 mum, which was kept unchanged when the sample surface was covered by a GaAs or Si plate. This work indicates the usefulness of the CSIP for application in passive LWIR microscopy.
[Show abstract][Hide abstract] ABSTRACT: A passive scanning confocal microscope in the long-wavelength infrared (LWIR) region has been developed for sensitive imaging of spontaneous LWIR radiation by utilizing an ultrahighly sensitive detector, called the charge-sensitive infrared phototransistor (CSIP). The microscope consisted of room-temperature components including a Ge objective lens and liquid helium temperature components including a confocal pinhole, Ge relay lenses, and CSIP detector. With the microscope, thermal radiation (wavelength of 14.7 microm) spontaneously emitted by the object was studied with a spatial resolution of 25 microm. Clear passive LWIR imaging pictures were obtained by scanning a sample consisting of glass, Al foil, Ag paste, and Au. Clear passive LWIR image was also obtained even when the sample surface was covered by a GaAs or Si plate. This work suggests usefulness of CSIP detectors for application of passive LWIR microscopy.
The Review of scientific instruments 07/2009; 80(6):063702. DOI:10.1063/1.3152224 · 1.61 Impact Factor
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