R. V. Shenoi

A Surface Plasmon Enhanced Infrared Photodetector Based on InAs Quantum Dots

In this paper, we report a successful realization and integration of a gold two-dimensional hole array (2DHA) structure with semiconductor InAs quantum dot (QD). We show experimentally that a properly designed 2DHA-QD photodetector can facilitate a strong plasmonic-QD interaction, leading to a 130% absolute enhancement of infrared photoresponse at the plasmonic resonance. Our study indicates two key mechanisms for the performance improvement. One is an optimized 2DHA design that permits an efficient coupling of light from the far-field to a localized plasmonic mode. The other is the close spatial matching of the QD layers to the wave function extent of the plasmonic mode. Furthermore, the processing of our 2DHA is amenable to large scale fabrication and, more importantly, does not degrade the noise current characteristics of the photodetector. We believe that this demonstration would bring the performance of QD-based infrared detectors to a level suitable for emerging surveillance and medical diagnostic applications.

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.

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.

Design of plasmonic photonic crystal resonant cavities for polarization sensitive infrared photodetectors

We design a polarization-sensitive resonator for use in mid-infrared photodetectors, utilizing a photonic crystal cavity and a single or double-metal plasmonic waveguide to achieve enhanced detector efficiency due to superior optical confinement within the active region. As the cavity is highly frequency and polarization-sensitive, this resonator structure could be used in chip-based infrared spectrometers and cameras that can distinguish among different materials and temperatures to a high degree of precision.

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.

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.

Investigation of multistack InAs/InGaAs/GaAs self-assembled quantum dots-in-double-well structures for infrared detectors

The authors report the InAs/InGaAs/GaAs/AlGaAs quantum dots-in-double-well (D-DWELL) design, which has a lower strain per DWELL stack than the InAs/InGaAs/GaAs DWELLs thereby enabling the growth of many more stacks in the detector. The purpose of this study is to examine the effects of varying the number of stacks in the double DWELL detector on its device performance. The structures are grown by solid source molecular beam epitaxy on GaAs substrates. After fabrication of single pixel devices, a series of device measurements such as spectral response, dark current, total current, and responsivity were undertaken and the photoconductive gain and the activation energies were extracted. The goal of these experiments is not only to optimize the device performance by optimizing the number of stacks but also to investigate the transport properties as a function of the number of stacks.

Plasmon assisted photonic crystal quantum dot sensors

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 metal-semiconductor 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.