Quantum Dot Infrared Photodetectors Research Articles

Spectral broadening due to post-growth annealing of a long-wave InGaAs/GaAs quantum dot infrared photodetector with a quaternary barrier layer

We present the effect of post-growth rapid thermal annealing on multilayer, uncoupled In0.50Ga0.50As/GaAs quantum dot infrared photodetectors (QDIPs) with a combination of quaternary In0.21Al0.21Ga0.58As and GaAs capping. Long wave photoresponse (~0.11eV or 10.2μm) with narrow spectral width (14%) is obtained from as-grown QDIPs. The spectral width increases to 45% for QDIP annealed at 800°C. It is likely that a large inter-diffusion effect because of annealing changes the composition of the quantum dots and capping layer, thus increasing the QDIP spectral width. Dark current as well as noise current is decreased for 650°C annealed QDIP compared to as-grown detector. Passivation of as-grown defect by post growth annealing predicted the improvement of dark current. Such improvement and broadening of characteristics may render such QDIPs suitable for use in broadband infrared imaging applications.

Quantum dot infrared photodetector with gated-mode design for mid-IR single photon detection

A novel design for a quantum dot infrared photodetector (QDIP) is proposed based on avalanche multiplication and is expected to be used as a single photon detector at mid-IR. A high field multiplication region is added to a conventional QDIP in separate absorption, charge, and multiplication structures to intensify incoming photocurrent generated in the absorption region. The absorption region of the photodetector consists of quantum dot layers that are responsible for absorption of mid-IR wavelengths. Because of higher operation voltages in gated-mode operation, resonant tunneling barriers are also included in the absorption region to prevent higher dark currents. The absorption region is designed for operation at λ=8 μm. During the gate pulse period, photo-generated electrons can trigger an avalanche and produce an output pulse. For this detector, the dark count rate (DCR) and single photon quantum efficiency (SPQE) are calculated at different temperatures. SPQE with peak of about 0.3 for T=50 K is obtained. For higher temperatures, about T=120 K, SPQE is very low due to the contribution of dark carriers generated in the quantum dot absorption region.

Design of large dynamic range, low‐power, high‐precision ROIC for quantum dot infrared photo‐detector

Hybrid infrared (IR) focal plane arrays consist of an array of IR photo-detectors, bump-bonded to a silicon CMOS readout integrated circuit (ROIC) chip. Design and optimisation of ROIC for quantum dot IR detectors is a multidimensional problem. The major design challenge is to select appropriate readout circuit topology to meet the large dynamic range requirement of quantum dot IR photo-detectors within the area dictated by the matched pixel size. Proposed is an efficient design optimisation for ROIC. The optimisation is based on a proposed decision matrix, which leads to a decision merit for ROIC design. Four main specifications, i.e. charge handling capacity, noise, power dissipation and detector bias voltage variations, have been considered. Various architectures have been compared using circuit design, simulation and implementation. The targeted ROIC specifications for a test chip containing a 4 × 4 array are: 5 Mē charge handling capacity, 30 × 30 µm maximum pixel size, snapshot mode of operation, variable integration time, 5 megapixels/s (Mpps) readout rate and readout noise of 600ē at ambient temperature. Also presented is a design with 5 Mē charge handling capacity, which has not been reported for 180 nm CMOS process earlier.

Backside-configured surface plasmonic structure with over 40 times photocurrent enhancement

In this paper, we report a quantum dot infrared photodetector (QDIP) enhanced by a backside-configured surface plasmonic structure with an over 40 times peak photocurrent enhancement. The QDIP enhancement by the backside-configured plasmonic structure is compared with that by the top-configured plasmonic structure. The backside-configured plasmonic structure shows much higher photocurrent and photodetectivity D* enhancement. We analyze the excitation of the surface plasmonic waves by the backside-configured and top-configured plasmonic structures. The higher enhancement is attributed to the more efficient surface plasmonic excitation by the backside-configured plasmonic structure.

Detectivity dependence of quantum dot infrared photodetectors on temperature

The detectivity of Quantum dot infrared photodetectors (QDIPs) has always attracted a lot attention as a very important performance parameter. In the paper, based on the theoretical model for the detectivity with the consideration of the common influence of the microscale electron transport, the nanoscale electron transport and the self-consistent potential distribution of the electrons, the dependence of the detectivity of the QDIP on temperature is discussed by analyzing the influence of the temperature on the average electrons number in a quantum dot. Specifically, the average electrons number in a quantum dot shows different change trends (from the increase to decrease) with the increase of the temperature, but the detectivity presents the single decrease trend with the temperature, which can provide the designers with the theoretical guidance for the performance optimization of the QDIP devices.

Noise characteristics investigation in quantum dot infrared photodetectors

The noise of quantum dot infrared photodetectors (QDIPs) can bring about the degradation on their performance, so keen interest has been paid to research on the noise in recent years. In this paper, a noise model of QDIP including the common influence of the microscale and the nanoscale electron transport to the activation energy is further verified at different temperatures, moreover, with the consideration of the dependence of the drift velocity on the electric field. The main concern is to investigate the influence of QDIPs parameters on the noise characteristics, such as the electric field, temperature, two electrons transport, detector material and structural performance parameters, respectively. The reasons for the influence of main performance parameters on the noise are analyzed and discussed in detail. The calculated and simulated results show that the noise model has a good agreement with the experimental data, and the research can provide the guidance in the optimization of the device design and the pursuit of the higher performance QDIP.

Evidence of long-wave-infrared excited state transition at high temperature (200 K) in 35-layer In0.50Ga0.50As/GaAs quantum dot infrared photodetector

Fabricating quantum dot infrared photodetectors (QDIPs) operable under high temperatures has remained a challenge. The authors report the performance of multispectrum 35-layer In0.50Ga0.50As/GaAs QDIP at high temperatures. Results showed three photoresponse peaks at ∼5.6, 7.4, and 11.5 μm. The third peak is observed only at 200 K, possibly because of transition of electrons from the second excited state of the quantum dot to GaAs barrier state. Peak responsivity value (∼140 mA/W) and maximum D* value (∼1.25 × 1010 cm·Hz1/2/W) is reached at 1.5 V. Responsivity is higher (210 mA/W) at 150 K than 77 K, possibly because of better transport of carriers at higher temperatures. The D* values are ∼4.33 × 108 cm·Hz1/2/W at 150 K and ∼3.3 × 106 cm·Hz1/2/W at 200 K at 1.0 V bias.

Photovoltaic operation of quantum dot quantum cascade detector with low photoconductive gain for midwave infrared photodetection

AbstractWe demonstrate photovoltaic operation of midwave (MW) quantum dot infrared photodetector (QDIP) with conventional n‐i‐n geometry, with a quantum cascade design. Quantum dot quantum cascade detector (QD‐QCD) provides zero bias operation with responsivity of 10 mA/W and detectivity of 9×109 cm.Hz1/2W‐1 at 77 K for f/2 optics. Measured photoconductive gain is below 0.4, which is difficult to obtain with the traditional QDIP architecture, and is highly attractive for focal plane array applications. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

More than one order enhancement in peak detectivity (D*) for quantum dot infrared photodetectors implanted with low energy light ions (H−)

In(Ga)As/GaAs-based quantum dot infrared photodetectors (QDIPs) have emerged as one of the most suitable devices for infrared detection. However, quantum dot devices suffer from lower efficiencies due to a low fill-factor (∼20%–25%) of dots. Here, we report a post-growth technique for improving the QDIP performance using low energy light ion (H−) implantation. At high bias, there is evidence of suppression in the field-assisted tunneling component of the dark current. Enhancement in peak detectivity (D*), a measure of the signal-to-noise ratio, by more than one order, from ∼109 to 2.44 × 1010 cm Hz1/2/W was obtained from the implanted devices.

FAR INFRARED PHOTO DETECTOR BASED ON ELECTROMAGNETICALLY INDUCED TRANSPARENCY

In this paper, we design a room temperature long wavelength quantum dot infrared photo detector (QDIP) by considering the principle of electromagnetically induced transparency (EIT) in a nanocrystal composed of a spherical GaAs quantum dot (QD) embedded in InAs . It is shown that the presence of long wavelength infrared (IR) signal in the medium affects on the absorption of visible optical probe (λp) in proposed photo detector. The far IR wavelength (λ FIR ) can be tuned to be 20 μm by means of external voltage and the size of QD. It is found that increasing the magnitude of far IR signal in the medium results in increase of optical probe signal absorption.

Improvement of QDIP performance due to quantum dots with built-in charge

The charging of quantum dots provides two strong effects which improve Quantum Dot Infrared Photodetector (QDIP) performance. First, electrons placed in the quantum dots enhance IR-induced transitions and increase electron coupling to IR radiation. Second, the built-in-dot charge creates potential barriers around dots and these barriers strongly suppress the photoelectron capture and exponentially increase the photoelectron lifetime. Both effects enhance the IR photoresponse. Long photoelectron lifetime decreases the generation–recombination noise and increases the device sensitivity. To investigate the potential profiles around charged dots, we used the nextnano3 software which allows for simulation of multilayer structures combined with realistic geometries in one, two, and three spatial dimensions. In weak electric fields the photoelectron kinetics and transport in the potential created by charged dots have been studied analytically. In strong fields the results were based on Monte-Carlo modeling. The effects of dot charging have been investigated in QD structures which were fabricated using molecular beam epitaxy. InAs quantum dots were grown on AlGaAs surfaces by deposition of approximately 2.1 monolayers of InAs. In the obtained structures the dot charging is realized via intra-dot and inter-dot doping. The increase in photoresponse due to dot charging is in good agreement with the model which takes into account anisotropy of potential barriers around QDs in QD layers.

Characteristics analysis of dark current in quantum dot infrared photodetectors

Since the dark current of quantum dot infrared photodetectors (QDIPs) can bring about great influence on their performance, they have attracted more and more attention in recent years. In this paper, a dark current model of the QDIP including the common influence of the microscale and the nanoscale electron transport is further verified at different temperatures, moreover, with account taken of the dependence of the drift velocity of electrons on the applied electrical field. The main concern is to discuss the influence of QDIPs parameters on the dark current characteristics, such as the applied electrical field, operation temperatures, two electrons transport (microscale and nanoscale), and different material performance (mobility of electrons, effective mass of electrons, and saturation velocity of electrons), respectively. The reasons for the influence of each performance parameters on the dark current are investigated in detail. The calculated and simulated results show that the dark current model has an excellent agreement with the experimental data, and the research on the influence of each parameter on dark current can guide the design and improve the performance of the QDIP.

Optimizing light absorption in quantum dot infrared photodetectors by tuning surface confinement of surface plasmonic waves

In this paper, we measured the transmission of the 2DSHA surface plasmonic structures and its variation with the hole diameters a of the 2DSHA structures. The relationship between the transmission and the hole diameters a is found to be different from the prediction of Bethe's diffraction theorem. We also found that the photocurrent of the quantum dot (QD) infrared photodetectors (QDIPs) with different QD active layer thicknesses show different dependence on the hole diameters a of the 2DSHA structures. The photocurrent of the QDIPs with 10 active QD layers (10-QDIPs) saturates and starts to decrease as the hole diameter a is larger than 1.6 µm, whereas that of the QDIPs with 20 active QD layers (20-QDIPs) increases linearly with the hole diameter. The difference in the hole-diameter dependence of the 10-QDIPs and the 20-QDIPs is attributed to the variation of the near-field spreading in the vertical (surface-normal) direction due to the change in the hole diameters. An over 6 time (6×) photocurrent enhancement is obtained by optimizing the hole diameter of the 2DSHA surface plasmonic structure.

A detailed investigation on the impact of post-growth annealing on the materials and device characteristics of 35-layer In0.50Ga0.50As/GaAs quantum dot infrared photodetector with quaternary In0.21Al0.21Ga0.58As capping

The effect of post-growth rapid thermal annealing on 35-layer In0.50Ga0.50As/GaAs quantum dot infrared photodetector (QDIP) with quaternary In0.21Al0.21Ga0.58As capping has been investigated. Transmission electron microscopy showed some as-grown defects were removed by post growth annealing treatment. An increase in the compressive strain in the heterostructure due to annealing was identified from X-ray diffraction curve. A two-color photoresponse in the long-wave region (8.5 and 10.2μm) was observed in both as-grown device and those annealed at 650°C temperature. A three-fold enhancement in peak responsivity was observed in the QDIPs annealed at 650°C (1.19A/W) compared to that in the as-grown (0.34A/W). Detectivity also increased by two fold from as-grown to 650°C annealed device. The changes are attributed to the removal of as-grown defects and dislocations during epitaxial growth. These removals changed the confinement potential profile, which resulted in an improvement in the detectivity and responsivity of the annealed sample.

Broadband InGaAs-capped InAs/GaAs quantum-dot infrared photodetector with Bi-modal dot height distributions

The influence of quantum-dot (QD) height distribution on the detection wavelengths of InGaAs-capped quantum-dot infrared photodetectors (QDIPs) is investigated. For devices with 2.8 and 2.0 mono-layer (ML) InAs coverage, 7.6 and 10.4 μm detection wavelengths are observed. The results suggest that reduced dot height would result in a longer detection wavelength. By using 2.4 ML InAs QDs with bi-modal dot height distributions, a 6–12 μm broadband QDIP is achieved with the combination of ∼8 and ∼10 μm peak detection wavelengths contributed by the larger and smaller InAs QDs.

Dark current and noise analyses of quantum dot infrared photodetectors

Because the dark current and the noise of quantum dot infrared photodetectors (QDIPs) can bring about a degradation in their performance, they have attracted more and more attention in recent years. In this paper, an algorithm used to evaluate the dark current of the QDIP is proposed, which is based on the algorithm including the common contribution of the microscale and the nanoscale electron transport. Namely, by accounting for the dependence of the drift velocity on the applied electric field, we greatly enhance the accuracy of the dark current calculation compared with that in the previous algorithm. This proposed algorithm is further used to estimate the noise current of QDIP, and the calculated results show a good agreement with the published data.

Cuboid GaN/AlGaN Quantum Dot Infrared Photodetector; Photoconductive gain and capture probability

We have carried out a detailed theoretical analysis for a Quantum Dot (QD) Infrared Photodetector (QDIP). A cuboid GaN QD embedded in Al0.2Ga0.8N has been considered as the unit cell of the active layer of the detector. We started with calculating the electronic structure of the dots, using the single band effective mass method. Quantum efficiency has been discussed subsequently by considering its temperature, QD size and density dependency. Photoconductive gain and capture probability of the device has been mentioned as another main objective of this paper. Their different structural and external applied dependencies calculated and compared with previous experimental and theoretical reports. It is found that the gain can indeed exhibit abroad range of values including up to several thousands, depending on bias, in the considered structure. Eventually, Responsivity of the detector considered as a figure of merit and discussed by detail.

Performance investigations of quantum dot infrared photodetectors

Quantum dot infrared photodetectors (QDIPs) have already attracted more and more attention in recent years due to a high photoconductive gain, a low dark current and an increased operating temperature. In the paper, a device model for the QDIP is proposed. It is assumed that the total electron transport and the self-consistent potential distribution under the dark conditions determine the dark current calculation of QDIP devices in this model. The model can be used for calculating the dark current, the photocurrent and the detectivity of QDIP devices, and these calculated results show a good agreement with the published results, which illustrate the validity of the device model.

Leaky-mode effects in plasmonic-coupled quantum dot infrared photodetectors

The effects of a heavily doped GaAs top contact layer on a plasmonics-integrated InAs quantum dot infrared photodetector (QDIP) are investigated. A metal photonic crystal (MPC), a 100 nm-thick gold film perforated with a 2.5 μm-period, 2-dimensional square hole array, is employed as a plasmonic coupler. The MPC is fabricated on QDIPs with identical structures except for the thickness (0.1 and 1.3 μm) of the top contact layer (doping concentration ∼2 × 1018 cm−3). For the lowest order surface plasma wave (SPW) resonance, the resonance wavelength undergoes a blue shift of 0.27 μm from 8.26 μm, and the responsivity and detectivity drop by ∼50% for the thicker contact layer. These effects are explained by leaky mode characteristics resulting from the free-carrier-reduced dielectric constant in the contact region that impacts the SPW resonance.

Self‐assembled InGaAs/GaAs quantum dot photodetector on germanium substrate

AbstractWe are reporting the growth of 30 layer self‐assembled InGaAs/GaAs quantum dot infrared photodetector (QDIP) structures on Ge substrate where a proper interface formation procedure was followed to minimise the defect density at the GaAs/Ge interface. The interface formation technique includes deposition of a migration enhanced epitaxy (MEE) grown GaAs layer followed by deposition of a thin GaAs layer grown with multiple annealing steps in between. The structural and optical properties of the heterostructure are evaluated by Transmission Electron Microscopy (TEM) and Photoluminescence (PL). The I‐V curve for the grown device structure has been demonstrated. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)