It has recently been reported that by using a spectral-tuning algorithm, the photocurrents of multiple detectors with spectrally overlapping responsivities can be optimally combined to synthesize, within certain limits, the response of a detector with an arbitrary responsivity. However, it is known that the presence of noise in the photocurrent can degrade the performance of this algorithm significantly, depending on the choice of the responsivity spectrum to be synthesized. We generalize this algorithm to accommodate noise. The results are applied to quantum-dot mid-infrared detectors with bias-dependent spectral responses. Simulation and experiment are used to show the ability of the algorithm to reduce the adverse effect of noise on its spectral-tuning capability.

We report high performance infrared sensors that are based on intersubband transitions in nanoscale self-assembled quantum dots combined with a microcavity resonator made with a high-index-contrast two-dimensional photonic crystal. The addition of the photonic crystal cavity increases the photocurrent, conversion efficiency, and the signal to noise ratio ͑represented by the specific detectivity D * ͒ by more than an order of magnitude. The conversion efficiency of the detector at V b = −2.6 V increased from 7.5% for the control sample to 95% in the PhC detector. In principle, these photonic crystal resonators are technology agnostic and can be directly integrated into the manufacturing of present day infrared sensors using existing lithographic tools in the fabrication facility. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2194167͔ Infrared sensors in the wavelength range of 3 -25 m are of immense technological importance due to their application in medical diagnostics, fire-fighting equipment, and night vision systems. Quantum dot infrared photodetectors have been identified as an emerging technology for this wavelength regime due to their low dark current leading to a potentially higher operating temperature and normal incidence operation based on a mature GaAs technology. [1][2][3][4][5] Presently, high performance midinfrared detectors are based on mercury cadmium telluride ͑MCT͒. Due to a dramatic change of the band gap as a function of material composition, it is very challenging to reproducibly obtain large area homogeneous materials suitable for large area focal plane arrays ͑FPA͒ based on this material system. In contrast, mature materials growth technologies for III-V semiconductors can provide very accurate control of compositions and homogeneity. Therefore there is interest in developing IR photodetectors using III-V materials. One of the most promising III-V semiconductor long wavelenght infrared ͑LWIR͒ detectors is the quantum well infrared photodetector ͑QWIP͒, 6-9 which employs the intersubband or the subbandto-continuum transitions in quantum wells. One of the drawbacks of n-type QWIPs is that they cannot detect normally incident light due to the restriction of selection rules for the optical transition. In contrast, the intersubband optical transitions in quantum dots ͑QDs͒ do not have that restriction, due to the three-dimensional quantum confinement. Theoretically, quantum dot infrared photodetectors ͑QDIPs͒ and quantum dot-in well ͑DWELL͒ detectors ͑which is a combination of a quantum dot and quantum well detector͒ offer several advantages over QWIPs, including lower dark current ͑hence higher T operation͒, higher responsivity, normal incidence detection, and improved radiation hardness. 10,11 QDIPs with low dark current densities and high operating temperature have been reported. 2,3 Asymmetrically designed DWELL detectors have also been shown to have a biasdependent spectral response that is suitable for multispectral imagery. 12 Recently, a two color 320ϫ 256 FPA, based on a volt...

We report the growth and fabrication of midwave infrared InAs/ GaSb strain layer superlattice ͑SLS͒ detectors. Growth of alternate interfaces leads to a reduced strain between the GaSb buffer and SLS ͑⌬a ʈ / a =−5ϫ 10 −4 ͒, enabling the growth of active regions up to 3 m ͑625 periods͒. The structural, optical, and electrical properties of the active region were characterized using x-ray crystallography and photoluminescence, respectively. p-in detectors were grown using 625 periods of 8 ML ͑monolayer͒ InAs/8 ML GaSb as the active region. The cutoff for the detectors was 4.6 m with a conversion efficiency of 32% at V b = −0.2 V. Detectivity was obtained using noise power spectral density measurements under 300 K 2 field of view illumination and was equal to 5.2ϫ 10 10 and 3 ϫ 10 10 cm Hz 1/2 /W ͑V b = −0.02 V, T =80 K͒ in the white noise and 1 / f noise limit ͑at 50 Hz͒.

The effects of doping on InAs/ In 0.15 Ga 0.85 As quantum dots-in-well infrared photodetectors have been investigated by measuring the dark current, photocurrent, spectral response, responsivity, and detectivity. The dark current increased monotonically as a function of the doping level in the dots. The photocurrent too increased with the increase in the doping level. By measuring the background limited infrared photodetector temperature, we find that the optimum sheet doping concentration in these detectors is n =3ϫ 10 10 cm −2 ͑corresponding to about 1e / dot͒. These results were corroborated by measurement of responsivity and generation-recombination noise limited detectivity of these detectors.

The authors demonstrate the design, growth, fabrication, and characterization of resonant cavity enhanced InAs∕In0.15Ga0.85As dots-in-a-well (RC-DWELL) quantum dot infrared photodetector (QDIP) and compare it with a standard DWELL detector. They measured peak photoresponse at the resonant wavelength of 9.5μm for the RC-DWELL photodetector. The peak responsivity was measured to be 0.76A∕W at 1.4V and the peak detectivity was 1.4×1010cmHz1∕2∕W at 0.5V at a temperature of 77K. The photocurrent density increased in comparison with the standard DWELL structure with the same active region by a factor of 6 at Vb=2.1V and 80K. A factor of 6 increase in responsivity and factor of 3 increase in detectivity at 1.2V and 77K were also observed in the resonant cavity enhanced DWELL sample. The quantum efficiencies for the RC-DWELL sample were calculated to be ∼10% at 9.5μm and 1.25% at 10μm for the standard DWELL sample. They conclude that the RC-DWELL is a promising improvement for QDIP-based infrared detection applications.

Resonant cavity enhanced In As ∕ In 0.15 Ga 0.85 As dots-in-a-well quantum dot infrared photodetector InAs quantum dot infrared photodetectors with In 0.15 Ga 0.85 As strain-relief cap layersThe effects of doping on InAs/ In 0.15 Ga 0.85 As quantum dots-in-well infrared photodetectors have been studied by measuring the dark current, photocurrent, and spectral response. A significant reduction of dark current with decrease in doping concentration in the quantum dots has been observed. However, the photocurrent of the detectors increases with the doping. By measuring the background limited infrared photodetector temperature, we find that the optimum sheet doping concentration in these detectors is n =3ϫ 10 10 cm −2 ͑corresponding to about one electron per dot͒.

Optimization of various growth parameters for Type-II GaSb(10MLs)/InAs(10MLs) nanoscale superlattices (SL) and GaSb layers, grown by solid molecular beam epitaxy, has been undertaken. We present optical and structural characterization for these heterostructures, using high resolution X-ray diffraction (HRXRD), photoluminescence (PL) and atomic force microscopy (AFM). Optimized parameters were then used for growth of InAs/GaSb SLs photovoltaic detectors (λ cut-off ~5 µm) operating at room temperature. By controlling the nature of interfaces, the in-plane mismatch between GaSb-buffer layer and SLs can be reduced enabling the growth of active regions up to 3µm. Normal incidence single pixel photodiodes were fabricated using standard lithography with apertures ranging from 25-300 µm in diameter. The spectral response from the SLs detector was observed at room temperature. This suggests the potential of the SLs technology for realizing high operating temperature (HOT) sensors. Responsivity measurements were also undertaken using a calibrated black body source, 400Hz optical chopper, SR 770 FFT Network signal analyzer and Keithley 428 preamplifier. We obtained current responsivity equal 2.16 A/W at V = -0.3V(300K). The Johnson noise limited D* at 300K was estimated to be 4.6 ×10 9 cm⋅Hz 1/2 /W at V = -0.3V

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