This paper is NOT THE PUBLISHED VERSION; but the author's final, peer-reviewed manuscript. The published version may be accessed by following the link in th citation below.

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.

Ultrafast differential transmission spectroscopy is used to explore temperature-dependent carrier dynamics in an InAs/InGaAs quantum dots-in-a-well heterostructure. Electron-hole pairs are optically injected into the three dimensional GaAs barriers, after which we monitor carrier relaxation into the two dimensional InGaAs quantum wells and the zero dimensional InAs quantum dots by tuning the probe photon energy. We find that carrier capture and relaxation are dominated by Auger carrier-carrier scattering at low temperatures, with thermal emission playing an increasing role with temperature. Our experiments provide essential insight into carrier relaxation across multiple spatial dimensions.

reconstructing the spectral shape of materials in the MWIR and LWIR wavelengths using only experimental photocurrent measurements from quantum dot infrared photodetectors (QDIPs). The algorithm theory and implementation will be described, followed by an investigation into this algorithmic spectrometer's performance. Compared to the QDIPs utilized in an earlier implementation, the QDIPs used have highly varying spectral shapes and four spectral peaks across the MWIR and LWIR wavelengths. It has been found that the spectrometer is capable of reconstructing broad spectral features of a range of band pass infrared filters between wavelengths of 4µm and 12µm as well as identifying absorption features as narrow as 0.3µm in the IR spectrum of a polyethylene sheet.Index Terms-Algorithmic spectrometer, hyperspectral imaging, multispectral imaging, quantum dot infrared photodetectors.

We report Quantum Dot Infrared Detectors (QDIP) where light coupling to the self assembled quantum dots is achieved through plasmons occurring at the metal-semiconductor interface. The detector structure consists of an asymmetric InAs/InGaAs/GaAs dots-in-a-well (DWELL) structure and a thick layer of GaAs sandwiched between two highly doped n-GaAs contact layers, grown on a semi-insulating GaAs substrate. The aperture of the detector is covered with a thin metallic layer which along with the dielectric layer confines light in the vertical direction. Sub-wavelength two-dimensional periodic patterns etched in the metallic layer covering the aperture of the detector and the active region creates a micro-cavity that concentrate light in the active region leading to intersubband transitions between states in the dot and the ones in the well. The sidewalls of the detector were also covered with metal to ensure that there is no leakage of light into the active region other than through the metal covered aperture. An enhanced spectral response when compared to the normal DWELL detector is obtained despite the absence of any aperture in the detector. The spectral response measurements show that the Long Wave InfraRed (LWIR) region is enhanced when compared to the Mid Wave InfraRed (MWIR) region. This may be due to coupling of light into the active region by plasmons that are excited at the metalsemiconductor interface. The patterned metal-dielectric layers act as an optical resonator thereby enhancing the coupling efficiency of light into the active region at the specified frequency. The concept of plasmon-assisted coupling is in principle technology agnostic and can be easily integrated into present day infrared sensors.