Thomas E. Vandervelde

A multispectral and polarization-selective surface-plasmon resonant midinfrared detector

We demonstrate a multispectral polarization sensitive midinfrared dots-in-a-well photodetector utilizing surface-plasmonic resonant elements, with tailorable frequency response and polarization selectivity. The resonant responsivity of the surface-plasmon detector shows an enhancement of up to five times that of an unpatterned control detector. As the plasmonic resonator involves only surface patterning of the top metal contact, this method is independent of light-absorbing material and can easily be integrated with current focal plane array processing for imaging applications.

Progress in Infrared Photodetectors Since 2000

The first decade of the 21st-century has seen a rapid development in infrared photodetector technology. At the end of the last millennium there were two dominant IR systems, InSb- and HgCdTe-based detectors, which were well developed and available in commercial systems. While these two systems saw improvements over the last twelve years, their change has not nearly been as marked as that of the quantum-based detectors (i.e., QWIPs, QDIPs, DWELL-IPs, and SLS-based photodetectors). In this paper, we review the progress made in all of these systems over the last decade plus, compare the relative merits of the systems as they stand now, and discuss where some of the leading research groups in these fields are going to take these technologies in the years to come.

Low-strain InAs∕InGaAs∕GaAs quantum dots-in-a-well infrared photodetector

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 ...

Reduction in dark current using resonant tunneling barriers in quantum dots-in-a-well long wavelength infrared photodetector

We report the use of resonant tunneling (RT) assisted barriers to reduce the dark current in quantum dots-in-a-well (DWELL) infrared photodetectors. Designed RT barriers allow energy-selective extraction of photoexcited carriers while blocking a continuum of energies. Over two orders of magnitude reduction in the dark current in the RT-DWELL device over a control sample without RT-DWELL at 77K has been demonstrated. Specific detectivity (D*) of 3.6×109cmHz1∕2W−1 at 77K at λpeak=11μm with a conversion efficiency of 5.3% was obtained in the RT-DWELL device. D* for the RT-DWELL device is five times higher than that of the control sample.

Demonstration of Bias-Controlled Algorithmic Tuning of Quantum Dots in a Well (DWELL) MidIR Detectors

The quantum-confined Stark effect in intersublevel transitions present in quantum-dots-in-a-well (DWELL) detectors gives rise to a midIR spectral response that is dependent upon the detectors operational bias. The spectral responses resulting from different biases exhibit spectral shifts, albeit with significant spectral overlap. A postprocessing algorithm was developed by Sakoglu that exploited this bias-dependent spectral diversity to predict the continuous and arbitrary tunability of the DWELL detector within certain limits. This paper focuses on the experimental demonstration of the DWELL-based spectral tuning algorithm. It is shown experimentally that it is possible to reconstruct the spectral content of a target electronically without using any dispersive optical elements for tuning, thereby demonstrating a DWELL-based algorithmic spectrometer. The effects of dark current, detector temperature, and bias selection on the tuning capability are also investigated experimentally.

Resonant Tunneling Barriers in Quantum Dots-in-a-Well Infrared Photodetectors

The use of resonant tunneling (RT) barriers in the design of quantum dots-in-a-well (DWELL) infrared photodetectors is reported. The design of RT barriers for a variety of goals has been discussed. For simple DWELL designs, we demonstrate 2-3 orders-of-magnitude reduction in the dark current, with significant increase in the specific detectivity (D *) of the device. Two RT barriers are designed to selectively extract midwave and longwave components of the spectral response. We also report the use of RT barriers on strain-optimized quantum dots-in-a-double-well (DDWELL) structures to achieve very low dark current levels with peak D * of 2.9 ×1010 cm· Hz1/2 /W for a longwave infrared detection. Ability to select a particular wavelength in the spectral response is demonstrated with DDWELL architectures as well.

Quantum Dots-in-a-Well Focal Plane Arrays

In this paper, the basics and some of the recent developments in quantum dots-in-a-well (DWELL) focal plane arrays (FPAs) are reviewed. Fundamentally, these detectors represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP), in which the active region consists of quantum dots (QDs) embedded in a quantum well (QW). This hybridization grants DWELLs many of the advantages of its components. These advantages include normally incident photon sensitivity without gratings or optocoupers, like QDIPs, and reproducible control over operating wavelength through ldquodial-in recipesrdquo as seen in QWIPs. Recently reported high-temperature operation results for DWELL FPAs now back up the conclusions drawn by the long carrier lifetimes observed in DWELL heterostructures using femtosecond spectroscopy. This paper will conclude with a preview of some upcoming advances in the field of DWELL FPAs.

Multispectral Quantum Dots-in-a-Well Infrared Detectors Using Plasmon Assisted Cavities

We present the design, fabrication, and characterization, of multi-spectral quantum dots-in-a-well (DWELL) infrared detectors, by the integration of a surface plasmon assisted resonant cavity with the infrared detector. A square lattice and rectangular lattice cavity, formed by modifying the square lattice have been used in this design. By confining the resonant mode of the cavity to detector active region, the detector responsivity and detectivity have been improved by a factor of 5. A spectral tuning of 5.5 to 7.2 ¿m has been observed in the peak response of the detectors, by tuning the lattice constant of the cavity. Simulations indicate the presence of two modes of absorption, which have been experimentally verified. The use of a rectangular lattice predicts highly polarization sensitive modes in x- and y-direction, which are observed in fabricated detectors. A peak detectivity of 3.1 x 109 cm·¿{Hz} /W was measured at 77 K. This design offers a cost-effective and simple method of encoding spectral and polarization information, in infrared focal plane arrays.

Stable high temperature metamaterial emitters for thermophotovoltaic applications

We report a metamaterial design for a thermophotovoltaic (TPV) emitter. TPVs are similar to photovoltaic solar cells, but they convert heat to electricity instead of sunlight. The focus of this paper is on the emitter stage of the TPV system, which converts the heat into a spectral band which is easily absorbable by the TPV photodiode. The proposed structure consists of a platinum metallic element, an alumina dielectric spacer, and platinum grounding plane on a sapphire substrate. This perfect absorber based metamaterial emitter is shown to robustly operate at 600 °C. This temperature is high enough to enable TPV use for many industrial applications.

Growth of quantum fortress structures in Si1−xGex/Si via combinatorial deposition

This study details the evolution of morphologies in the Si1−xGex/Si system, under kinetically controlled conditions of 550 °C growth temperature and 1 A/s growth rate. We find that, with increasing film thickness and Ge fraction, a series of three-dimensional structures develop, starting from pits, and leading to quantum fortresses and ridges. The quantum fortress structures are of special significance because of their potential application in quantum cellular automata. We establish approximate boundaries in the parameter space of film thickness and Ge fraction, in which these structures form. We present a simple model, based on kinetics and strain, to explain the observed structures.