S. G. Matsik

Three-color (λp1∼3.8 μm, λp2∼8.5 μm, and λp3∼23.2 μm) InAs/InGaAs quantum-dots-in-a-well detector

We report a three-color InAs/InGaAs quantum-dots-in-a-well detector with center wavelengths at ∼3.8, ∼8.5, and ∼23.2 μm. We believe that the shorter wavelength responses (3.8 and 8.5 μm) are due to bound-to-continuum and bound-to-bound transitions between the states in the dot and states in the well, whereas the longer wavelength response (23.2 μm) is due to intersubband transition between dot levels. A bias-dependent activation energy ∼100 meV was extracted from the Arrhenius plots of the dark currents, which is a factor of 3 larger than that observed in quantum-well infrared photodetectors operating at comparable wavelengths.

Design and optimization of GaAs∕AlGaAs heterojunction infrared detectors

Design, modeling, and optimization principles for GaAs∕AlGaAs heterojunction interfacial workfunction internal photoemission (HEIWIP) infrared detectors for a broad spectral region are presented. Both n-type and p-type detectors with a single emitter or multiemitters, grown on doped and undoped substrates are considered. It is shown that the absorption, and therefore responsivity, can be increased by optimizing the device design. Both the position and the strength of the responsivity peaks can be tailored by varying device parameters such as doping and the thickness. By utilizing a resonant cavity architecture, the effect of a buffer layer on the response is discussed. Model results, which are in good agreement with the experimental results, predict an optimized design for a detector with a peak response of 9A∕W at 26μm with a zero response threshold wavelength λ0=100μm. For a λ0=15μm HEIWIP detector, background limited performance temperature (BLIP temperature), for 180° field of view (FOV) is expected a...

AlGaAs emitter∕GaAs barrier terahertz detector with a 2.3 THz threshold

A heterojunction interfacial work function internal photoemission (HEIWIP) detector with a threshold frequency (f0) of 2.3 THz (λ0=128μm) is demonstrated. The threshold limit of ∼3.3THz (92 μm) due to the Al fraction being limited to ∼0.005, in order to avoid control and transition from alloy to isoelectronic doping behavior, was surpassed using AlGaAs emitters and GaAs barriers. The peak values of responsivity, quantum efficiency, and the specific detectivity at 9.6 THz and 4.8 K for a bias field of 2.0kV∕cm are 7.3A∕W, 29%, 5.3×1011 Jones, respectively. The background-limited infrared photodetector temperature of 20 K with a 60° field of view was observed for a bias field of 0.15kV∕cm. The f0 could be further reduced toward ∼1THz regime (∼300μm) by adjusting the Al fraction to offset the effect of residual doping, and/or lowering the residual doping in the barrier, effectively lowering the band bending.

GaN∕AlGaN ultraviolet/infrared dual-band detector

Group III-V wide band gap materials are widely used in developing solar blind, radiation-hard, high speed optoelectronic devices. A device detecting both ultraviolet (UV) and infrared (IR) simultaneously will be an important tool in fire fighting and for military and other applications. Here a heterojunction UV/IR dual-band detector, where the UV/IR detection is due to interband/intraband transitions in the Al0.026Ga0.974N barrier and GaN emitter, respectively, is reported. The UV threshold observed at 360nm corresponds to the band gap of the Al0.026Ga0.974N barrier, and the IR response obtained in the range of 8–14μm is in good agreement with the free carrier absorption model.

Uncooled infrared detectors for 3–5μm and beyond

Avoiding cryogenic cooling not only reduces the cost and weight but also simplifies the infrared detector system allowing widespread usage. Here an uncooled infrared detection using intravalence bands is reported. A set of three p-GaAs∕AlxGa1−xAs multiple heterojunction detector structures were used to demonstrate the concept experimentally. A preliminary detector showed peak responsivity of 0.29mA∕W at 2.5μm at 300K. The intravalence band approach can be used to cover various wavelength ranges by using different material systems giving rise to the possibilities of a dual band detector operating in atmospheric windows.

GaAs/InGaAs quantum well infrared photodetector with a cutoff wavelength at 35 μm

GaAs/InGaAs far-infrared quantum well photodetectors based on a bound-to-continuum intersubband transition with a (zero response) cutoff wavelength of 35 μm are reported. A peak responsivity of 0.45 A/W and detectivity of 6.0×109 cmHz/W at a wavelength of 31 μm and a temperature of 4.2 K have been experimentally achieved. Infrared response was observed at temperatures up to 18 K. A calculated responsivity spectrum using a bound-to-continuum line shape corrected for phonon absorption is fitted to the experimental response. The calculated line shape without absorption gives a cutoff wavelength of 38 μm with a peak responsivity of 0.50 A/W and a detectivity of 6.6×109 cmHz/W at 32 μm.

GaAs/AlGaAs quantum well photodetectors with a cutoff wavelength at 28 μm

We demonstrate the longest (λc=28.6 μm) far-infrared quantum well photodetectors (QWIPs) based on a bound-to-bound intersubband transition in GaAs/AlGaAs. The responsivity is comparable with that of mid-infrared GaAs/AlGaAs and InGaAs/GaAs QWIPs. A peak responsivity of 0.265 A/W and detectivity of 2.5×109 cmHz/W at a wavelength of 26.9 μm and 4.2 K have been achieved. Based on the temperature dependent dark current and responsivity results, it is expected that similar performance can be obtained at least up to 20 K.

Bias-selectable tricolor tunneling quantum dot infrared photodetector for atmospheric windows

A tricolor infrared detector with bias-selectable peaks based on tunneling quantum dot infrared photodetector (T-QDIP) architecture is demonstrated. Photoabsorption takes place in In0.4Ga0.6As quantum dots (QDs) and the excited electrons are collected by resonant tunneling across an Al0.2Ga0.8As∕In0.1Ga0.9As∕Al0.2Ga0.8As double barrier coupled to the QDs. The field dependent tunneling for excited carriers in T-QDIP is used to select the operating wavelength. This T-QDIP detector exhibits three distinct response peaks at 4.5∕4.9±0.05, 9.5±0.05, and 16.9±0.1μm up to 80K. The peak detectivity is in the range of (1.0–6.0)×1012Jones at 50K. Bias polarity allows the selection of either the 9.5μm or the 16.9μm peak.

Heterojunction wavelength-tailorable far-infrared photodetectors with response out to 70 μm

Results are presented on the performance of a heterojunction interfacial workfunction internal photoemission (HEIWIP) wavelength-tailorable detector. The detection mechanism is based on free-carrier absorption in the heavily doped emitter regions and internal emission across a workfunction barrier caused by the band gap offset at the heterojunction. The HEIWIP detectors have the high responsivity of free-carrier absorption detectors and the low dark current of quantum well infrared photodector type detectors. For a 70±2 cutoff wavelength detector, a responsivity of 11 A/W and a D*=1×1013 cmHz/W with a photocurrent efficiency of 24% was observed at 20 μm. From the 300 K background photocurrent, the background limited performance (BLIP) temperature for this HEIWIP detector was estimated to be 15 K. This HEIWIP detector provides an exciting approach to far-infrared detection.

Cutoff tailorability of heterojunction terahertz detectors

Heterojunction interfacial work function internal photoemission (HEIWIP) detectors provide an interesting approach to the development of quantum detectors for the terahertz range. In this letter, the cutoff frequency/wavelength variation of HEIWIP detectors having different Al fractions in AlGaAs/GaAs structures is experimentally verified, and a model is presented for designing the structures. A key feature of HEIWIP responsivity is the ability to cover a broad frequency range in a single detector with cutoff tailorability by adjusting the Al fraction in the barrier regions. Extending the response to lower frequencies by the use of AlGaAs emitters and GaAs barriers is also discussed.