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The authors report the design, growth, fabrication, and characterization of a low-strain quantum dots-in-a-well (DWELL) infrared photodetector. This novel DWELL design minimizes the inclusion of the lattice-mismatched indium-containing compounds while maximizing the absorption cross section by enabling larger active region volume. The improved structure uses an In0.15Ga0.85As∕GaAs double well structure with Al0.10Ga0.90As as the barrier. Each layer in the active region was optimized for device performance. Detector structures grown using molecular beam epitaxy were processed and characterized. This new design offers high responsivity of 3.9A∕W at a bias of 2.2V and a detectivity of 3×109 Jones at a bias of 2.2V for a wavelength of 8.9μm. These detectors offer significant improvement in the responsivity while retaining the long wave infrared spectral properties of the InAs∕In0.15Ga0.85As∕GaAs DWELL. These detectors if coupled with improved noise characteristics could enable higher temperature operation of DWELL detectors, thus reducing the dependence on cooling equipment.
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.
A pulsed midinfrared photoconductivity study of electron recapture in dot-in-a-well infrared photodetectors yields bias-dependent electron-capture lifetimes in the range of 3 -600 ns and photoconductive gain factors of ϳ10 4 -10 5 . The dependence of the lifetimes on temperature and electric field argues for these surprisingly long values being due to electron intervalley transfer. Under normal device operating conditions, photoexcited electrons transfer efficiently out of the central GaAs ⌫ minimum into the high energy L and X valleys, where they couple only weakly to the ⌫-like confined states in the InAs dots.
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