A. G. U. Perera

Characteristics of a tunneling quantum-dot infrared photodetector operating at room temperature

We report high-temperature (240–300K) operation of a tunneling quantum-dot infrared photodetector. The device displays two-color characteristics with photoresponse peaks at ∼6μm and 17μm. The extremely low dark current density of 1.55A∕cm2 at 300K for 1V bias is made possible by the tunnel filter. For the 17μm absorption, the measured peak responsivity is 0.16A∕W (300K) for a bias of 2V and the specific detectivity D* is 1.5×107cmHz1∕2∕W (280K) for a bias of 1V. Excellent performance characteristics are also measured for the 6μm photoresponse.We report high-temperature (240–300K) operation of a tunneling quantum-dot infrared photodetector. The device displays two-color characteristics with photoresponse peaks at ∼6μm and 17μm. The extremely low dark current density of 1.55A∕cm2 at 300K for 1V bias is made possible by the tunnel filter. For the 17μm absorption, the measured peak responsivity is 0.16A∕W (300K) for a bias of 2V and the specific detectivity D* is 1.5×107cmHz1∕2∕W (280K) for a bias of 1V. Excellent performance characteristics are also measured for the 6μm photoresponse.

High-performance mid-infrared quantum dot infrared photodetectors

Quantum dot infrared photodetectors (QDIPs) have emerged as attractive devices for sensing long wavelength radiation. Their principle of operation is based on intersublevel transitions in quantum dots (QDs). Three-dimensional quantum confinement offers the advantages of normal incidence operation, low dark currents and high-temperature operation. The performance characteristics of mid-infrared devices with three kinds of novel heterostructures in the active region are described here. These are a device with upto 70 QD layers, a device with a superlattice in the active region, and a tunnel QDIP. Low dark currents (1.59 A cm−2 at 300 K), large responsivity (2.5 A W−1 at 78 K) and large specific detectivity (1011 cm Hz1/2 W−1 at 100 K) are measured in these devices. It is evident that QDIPs will find application in the design of high-temperature focal plane arrays. Imaging with small QD detector arrays using the raster scanning technique is also demonstrated.

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.

A resonant tunneling quantum-dot infrared photodetector

A novel device-resonant tunneling quantum-dot infrared photodetector-has been investigated theoretically and experimentally. In this device, the transport of dark current and photocurrent are separated by the incorporation of a double barrier resonant tunnel heterostructure with each quantum-dot layer of the device. The devices with In/sub 0.4/Ga/sub 0.6/As-GaAs quantum dots are grown by molecular beam epitaxy. We have characterized devices designed for /spl sim/6 /spl mu/m response, and the devices also exhibit a strong photoresponse peak at /spl sim/17 /spl mu/m at 300 K due to transitions from the dot excited states. The dark currents in the tunnel devices are almost two orders of magnitude smaller than those in conventional devices. Measured values of J/sub dark/ are 1.6/spl times/10/sup -8/ A/cm/sup 2/ at 80 K and 1.55 A/cm/sup 2/ at 300 K for 1-V applied bias. Measured values of peak responsivity and specific detectivity D/sup */ are 0.063 A/W and 2.4/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W, respectively, under a bias of 2 V, at 80 K for the 6-/spl mu/m response. For the 17-/spl mu/m response, the measured values of peak responsivity and detectivity at 300 K are 0.032 A/W and 8.6/spl times/10/sup 6/ cm/spl middot/Hz/sup 1/2//W under 1 V bias.

NEGATIVE CAPACITANCE OF GAAS HOMOJUNCTION FAR-INFRARED DETECTORS

Bias, frequency and temperature-dependent capacitance characteristics of p-GaAs homojunction interfacial work-function internal photoemission (HIWIP) far-infrared detectors are reported. A strong negative capacitance phenomenon has been observed. Unlike in other devices, even up to 1 MHz in HIWIP, the negative capacitance value keeps increasing with frequency, giving a stronger effect. The origin of this effect is believed to be due to the carrier capture and emission at interface states. Fitting data based on charging-discharging current and the inertial conducting current model show good agreement with the experimental observations.

Characteristics of a multicolor InGaAs-GaAs quantum-dot infrared photodetector

A three-color quantum-dot infrared photodetector has been fabricated and characterized. The active absorption region consists of undoped In/sub 0.4/Ga/sub 0.6/As quantum dots separated by GaAs barriers. Intersublevel transitions of electrons in the quantum dots results in absorption peaks at /spl sim/3.5, 7.5, and 22 /spl mu/m. The devices were characterized at 80 K and 120 K. The dark current density is 10/sup -6/ A/cm/sup 2/ at 120 K for an applied bias of 1 V. The responsivity and specific detectivity D/sup */ are 0.07 A/W and 4.8/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W for the 7.5-/spl mu/m response at 80 K for an applied bias of 3 V.

Terahertz detection with tunneling quantum dot intersublevel photodetector

The characteristics of a tunnel quantum dot intersublevel photodetector, designed for the absorption of terahertz radiation, are described. The absorption region consists of self-organized In0.6Al0.4As∕GaAs quantum dots with tailored electronic properties. Devices exhibit spectral response from 20to75μm (∼4THz) with peak at ∼50μm. The peak responsivity and specific detectivity of the device are 0.45A∕W and 108cmHz1∕2∕W, respectively, at 4.6K for an applied bias of 1V. Response to terahertz radiation is observed up to 150K.

Bias effects in high performance GaAs homojunction far-infrared detectors

A high performance, bias tunable, p-GaAs homojunction interfacial workfunction internal photoemission far-infrared detector is demonstrated. A responsivity of 3.10±0.05 A/W, a quantum efficiency of 12.5%, and a detectivity D* of 5.9×1010 cmHz/W were obtained at 4.2 K for cutoff wavelengths from 80 to 100 μm. The bias dependences of the quantum efficiency, detectivity, and cutoff wavelength were measured and are well explained by the theoretical model. The effect of the layer number on detector performance and the uniformity of the detectors are discussed. A comparison with Ge:Ga photoconductive detectors suggests that similar or even better performance may be obtainable with a far-infrared detector.

A quantum ring terahertz detector with resonant tunnel barriers

The electronic properties of InAs/GaAs quantum rings and the characteristics of resonant tunnel intersubband terahertz detectors with quantum ring active regions have been studied. The electronic states of the quantum rings have been calculated and measured by the capacitance-voltage technique. The detectors exhibit extremely low dark current density values ∼5×10−5, 4.7×10−2, and 3.5×10−1 A/cm2 under a −1 V bias at 4.2, 80, and 300 K, respectively. Three prominent response peaks are observed at ∼6.5, 10, and 12.5 THz up to T=120 K. At 80 K, the responsivity of the peaks varies from 0.07 to 0.02 A/W.

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...