We fabricated extended SWIR photodetectors with cutoff wavelength of 2.3 μm by using lattice-matched InGaAs/GaAsSb type-II quantum wells as an absorption layer. The 100-pair InGaAs/GaAsSb quantum wells and InGaAs as a cap layer were grown on an n-type InP substrate by molecular-beam epitaxy. The p-n junction was formed by selective zinc diffusion using rapid thermal annealing. For dark current reduction, photodetector with a barrier layer between the absorbing layer and the cap layer was also fabricated. In each device, in addition to absorption in the InGaAs cap layer, absorption which is possibly originating from the quantum well layer was observed in a wavelength range from 1.6 μm to 2.3 μm. By comparing dark current of each device, dark current reduction by the barrier layer was also confirmed.
In this paper, we report enhanced performance of quantum dot infrared photodetector (QDIP) by means of surface plasmonic structure. A 10-layer InGaAs quantum dot (QD) structure with AlGaAs barriers were grown on GaAs(001) substrate by molecular beam epitaxy. A periodic gold pillar array was fabricated on the surface of the wafer by i-line lithography and ICP dry etching. The wafer was processed to form a circular mesa of 300 μm diameter. The pillar pitch was varied from 2.0 to 2.5 μm and the pillar diameter was varied from 1.1 to 1.6 μm. The detectors were illuminated from substrate side to evaluate spectral responsivity and detectivity D* at temperature T = 78 K. The pillar array was found to enhance the detector performance at particular wavelength which depends on the pillar property. We found the optimal property of the pillar array whose enhancement peak matches the QDIP's response peak at 7.7 μm. At that wavelength, the responsivity and detectivity were almost doubled compared to the detector without the pillar array.
In this report, mineral composition of rock samples including conglomerate, sandstone, and dolomite was analyzed by IR spectral imaging using QDIP focal plane arrays (FPAs) with a peak-responsivity wavelength of 6.5 μm (FPA 1) and 5.5 μm (FPA 2). The qualitative and quantitative analyses are presented, and the key factor that determines the quantitative precision is discussed. In the qualitative analysis, the luminance of the different components in the rock samples was compared in the image. In the FPA 1 images, the shell fossil in the conglomerate sample and the limestone in the sandstone sample were darker than the other parts of the rocks due to their low emittance at 6.5 μm. In contrast, the difference in the luminance is hardly observed in the FPA 2 images under the same conditions. In the quantitative analysis, the emittance of dolomite was measured. Ten points in the IR image were randomly selected and the average emittance was calculated. The obtained emittances were 0.544±0.012 (FPA 1) and 0.941±0.019 (FPA 2), which means the coefficient of variation of the emittance measurement is ±2.1%~2.2%. By calculating the propagation of error, the precision of thermocouples for monitoring the temperature of the rocks in the calibration contributes most significantly (73%) to the total error.
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