Quantum Dot Infrared Photodetectors Research Articles

A nanophotonic approach to signal-to-noise ratio of quantum dot infrared photodetectors with surface plasmonic excitation

A nanophotonic approach to the signal-to-noise ratio (SNR) of an InAs-based quantum dot infrared photodetector (QDIP) with surface plasmonic excitation is reported. A 100 nm-thick Au film, perforated with a 3.1 μm-period, 2-dimensional square array of holes, referred to as a metal photonic crystal (MPC), is employed as a plasmonic coupler for it. Under the irradiance on the MPC integrated atop the QDIP, the fundamental surface plasma wave (SPW) is excited along their interface at ∼10.3 μm in wavelength. It carries the near-field that interacts with the quantum dots (QDs) under the interface. Depending on the presence of the coupler, the QDIP generates two different current–voltage (I-V) characteristics; one from the QDs normally working without MPC and the other from those coupled to the SPW near-field with it. The two I-V’s unfold the signal and noise current of each case with photoconductive gain. In their relation, generation-recombination and shot noises which are correlated with the detector signal current are directly affected by the plasmonic coupling but other sources including thermal noise are not relevant to it. Relying on these differences, the I-V analysis allows the SNR of each case and shows ∼20× enhancement by the plasmonic coupling. It reveals that most of the noise current is attributed to thermal fluctuations inherent to the quantum confinement of the QDIP. The SNR lower than the quantum efficiency in plasmonic enhancement is addressed.

Modeling of dark current in semispherical quantum dot structures for infrared photodetection

Due to its tunable heterojunction bandgap and great sensitivity to normal incident illumination, the Quantum Dot Infrared Photodetectors (QDIPs) have received a lot of attention for the purpose of infrared sensing. It could be a very promising replacement for conventional infrared photodetectors made with established technology, including mercury cadmium telluride and quantum well infrared photodetectors. In this work, a model for the dark current in semispherical QDIP has been developed, resolves the primary semiconductor Poisson's and continuity equations, where the wave function and the bound states effects are investigated. In this study, Boltzmann transport equation in the photodetector active layer with embedded QDs is solved using the finite difference time domain method to determine the photodetector carrier mobility and its degradation due the quantum dot scattering. The outcomes of the presented have been contrasted with truncated conical QDIPs showing that smaller volume QDs had less noisy dark current. Investigations have been done into how the semispherical QDIP's dark current characteristics are affected by the QD volume, density, and operating temperature.

J–V characteristics of dark current in truncated conical quantum dot infrared photodetectors (QDIPs)

Quantum Dot Infrared Photodetector (QDIP) is one of the promising candidates for infrared photodetection due to its controllable heterojunction bandgap and sensitivity to normal incident radiation. It is expected to be superior to infrared photodetectors of mature technologies such as Mercury Cadmium Telluride (HgCdTe) or a quantum well infrared photodetector. In the presented paper, we have developed a theoretical model for the dark current in truncated conical QDIP as the truncated conical shaped QD structure is more appropriate to describe the fabricated dots. The dark current model is based on the drift diffusion model solving the main governing Poisson’s and continuity equations. In this model, the carrier mobility is calculated by solving time-dependent Boltzmann transport equation in the photodetector material with embedded truncated conical QDs using finite difference technique. The results of the developed model have been compared with the dark current characteristics with published experimental results of Indium Arsenide/Gallium Arsenide (InAs/GaAs) truncated QDIP. The effects of QD volume, QD aspect ratio and QD density and the operating temperature on the dark current characteristics have also been investigated.

Simulation and design of dual-band quantum dot infrared photodetector based on metal grating structure

Quantum dot infrared photodetectors (QDIP) have a weak ability to capture light, which limits the further improvement of absorptivity to a certain extent. Since the localized surface plasmon resonance (LSPR) can effectively couple the optical radiation energy and result in a significant field enhancement effect in the near-field range, it is introduced to improve the absorptivity of the QDIP. Concretely, the strip metal grating structure is coupled to the active region of the traditional QDIP, and a metal reflective layer is added at the bottom of the QDIP to improve the absorptivity by using the metal–semiconductor–metal structure. The simulation results show that the addition of the optimized strip metal grating structure can make the photon absorptivity of QDIP reach more than 90% in both frequency bands of 37.5 and 48.5 THz, and the coupling characteristics of LSPR are studied by the analysis of the electric field distribution of QDIP, which can provide the theoretical guidance for the combination of metal grating and traditional QDIP.

Study and optimization of structure InAs/InGaAs quantum dot in-a-well long-wave infrared photodetector

In this work, we have studied and simulated of electrical and optical properties The of InAs/InGaAs quantum dot in-a-well (DWELLs) long-wave infrared photodetector (IP). The effect of number and thickness of InAs quantum dot (QD) layers, as well as the InGaAs quantum well (QW) width on the quantum dot infrared photodetector (QDIPs) performance has been investigated. Our results have been shown that 30 quantum dots of 7 nm thickness and 6 nm well width give optimal values for responsivity, detectivity and noise equivalent power with values of 1.285 A/W, 7.66 * 1012 cm Hz1/2 W−1 and 10−11 W, respectively. In addition, the wavelength ranges detected in the same structure are medium infrared (4.47 µm), long infrared (11.47 µm) and very long infrared (22.08 µm) wavelength, respectively. These results confirm that InAs/InGaAs DWELL infrared photodetector performances are more sensitive to the structure geometry as well as their intrinsic parameters.

Modeling and characterization of carrier mobility for truncated conical quantum dot infrared photodetectors

In the present paper, a theoretical model for calculating the carrier mobility which is a result of the existence of a truncated conical quantum dots of n-type quantum dot infrared photodetectors (QDIPs) is developed. This model is built on solving Boltzmann’s transport equation that is a complex integro-differential equation describing the carrier transport. The time-domain finite-difference method is used in this numerical solution. The influences of dimensions and density of the QDs for this structure on the carrier mobility are studied. Eventually, the calculated mobility for truncated conical InAs/GaAs QDIP is contrasted to other conical, spherical, and hemispherical QD structures. The model put forward is a generic model that is applicable to various structures of truncated conical QDs devices.

Impact of quantum dot parameters on the performance of p-type quantum dot infrared photodetectors

In this work, the impact of the quantum dot parameters, including dot size, and material composition on the optoelectronic performance of quantum dot infrared photodetectors (QDIPs) is systematically studied. The QDIP is based on the intra-valence band transitions in Zn 1-x Cd x Se QDs. The eigen energies and wavefunction of the hole states are computed under the framework of the multi-band k.p model. The obtained electronic structure is further utilized to calculate the dark current density, responsivity, and detectivity of QDIPs. An increase in CdSe content markedly reduces the dark current density as well as improves the responsivity. As a result, detectivity enhances significantly. Raising the QD size also brings enhancement in the detectivity. Moreover, peak response wavelength depends on the CdSe content and dot dimensions. These results might provide new directions for the development of p-type II-VI QDs based QDIP. • Infrared photodiode based on the intervalence band absorption has been studied. • Strain dependent multiband effective mass k.p model is used to compute the electronic structure of QDs. • Higher CdSe content and larger quantum dot yields better optoelectronic performance. • The Peak response wavelength is quite sensitive to the CdSe content.

Hybrid strain-coupled multilayer SK and SML InAs/GaAs quantum dot heterostructure: Enabling higher absorptivity and strain minimization for enhanced optical and structural characteristics

The size and shape of self-assembled quantum dots (QDs) in the top layer of a strain-coupled multilayer Stranski-Krastanov (SK) type QD heterostructure is decided by the effect of strain from the bottom QD layers along with the compressive strain through InAs/GaAs interface. A novel approach is used in this article to grow the heterostructures such that QDs from one layer to the other are heterogeneously coupled resulting in reduced cumulative strain, which helps in formation of defect free and uniform dots even for 10 strain-coupled SK QD layers. Heterostructures with strain-coupled single- ( × 1), bi- ( × 2), tri- ( × 3), penta- ( × 5), hepta- ( × 7) and deca- ( × 10) layer SK QDs are grown employing a growth mechanism on six stack sub-monolayer (SML) type QDs, considering the individual advantages of SK and SML QDs. Full width half maximum (FWHM) calculated from the low temperature (19 K) photoluminescence (PL) are 50, 52, 54, 55, 56 and 50 nm for single, bi, tri, penta, hepta and deca-layer SK QD stack respectively, which shows uniform dot size distribution up to deca-layer SK QD structure because of the adapted growth mechanism. The activation energies calculated from temperature dependent PL are 244, 281, 299, 275, 288 and 397 meV for single, bi, tri, penta, hepta and deca-layers respectively, which aids that the strain-coupled deca-layer SK QD heterostructure has the highest activation energy compared to other strain-coupled multilayer SK QD structures. These properties make the deca-layer SK QD structure as the optimum device for quantum dot infrared photodetectors (QDIPs), which could operate at higher temperatures with improved performance parameters. High resolution X-ray diffraction (HRXRD) shows a defect free heterostructure with minimized hydrostatic strain and homogeneous dot size distribution for the strain-coupled deca-layer SK QD structure. Thus, the adapted growth mechanism along with heterogeneous coupling of SK and SML QDs facilitates higher absorption efficiency, increased carrier lifetime and better quantum confinement, making it a promising design to be used in intermediate band solar cells (IBSC) and QDIPs, where multilayer QDs are needed so as to improve the device performance.

Short-wave infrared (SWIR) photodetection by InAs/GaAs quantum dot heterostructures grown on Ge (100) substrate without Migration Enhanced Epitaxy layer

Integration of III-V based optoelectronic devices with Silicon (Si) technology is the prime choice of researchers for the futuristic Si-photonics. Profusion research is going on for direct growth of III-V heterostructures on the Germanium (Ge) substrate. Also, monolithic integration of III-V based device structures on Si using Ge layer and Migration Enhanced Epitaxy (MEE) technique have been endeavored. In this study, InAs based quantum dot infrared photodetectors (QDIPs) are grown on Ge substrate without MEE layers. The GaAs/AlAs superlattice buffer (SLB) layers are used to suppress the defects and dislocations. Two different QDIPs with GaAs capped and In 0.15 Ga 0.85 As/GaAs capped InAs QD are grown and characterized using photoluminescence (PL), high-resolution X-Ray Diffraction (HRXRD), and Raman spectroscopy (RS). Red-shifted and narrow PL spectrum of the InGaAs/GaAs capped QDIP with respect to the GaAs capped QDIP attributes to formation of larger dots and homogeneous size distribution. Low strain and high activation energy in the InGaAs capped QDs signify better strain relaxation via the InGaAs strain reducing layer (SRL) and better carrier confinement. Interband-assisted near-infrared (NIR) photoresponse is obtained from both devices till room temperature. However, the InGaAs/GaAs capped QDIP shows shortwave infrared (SWIR) response, which promulgates the formation of QDs with better crystallinity due to the presence of InGaAs SRL. The room temperature (300 K) dark current density of the GaAs and InGaAs capped QDIP is 1.2 × 10 −1 A/cm 2 and 6.6 × 10 −3 A/cm 2 respectively with −2 V bias voltage. This work demonstrates the pathway to uncomplicated growth of high quality QDIP structures on Ge substrate. • A novel technique is used to grow defect free InAs QD structures on Ge substrate. • GaAs/AlAs SLB layers are used to suppress the defects and dislocations. • InAs QDs with GaAs and InGaAs/GaAs capping are investigated and compared. • Both structures show low dark current at room temperature. • Infrared photoresponse till room temperature is obtained for both QDIPs.

Optimization of vertical strain coupling in InAs/GaAs p-i-p quantum dot infrared photodetectors with applied growth strategy

The authors report the optimization of vertically coupled active layers of InAs quantum dots (QDs) grown epitaxially following a unique in-situ growth strategy to achieve controlled strain propagation in subsequent layers resulting in homogenous dot-size distribution. The analysis comprises of bi, tri, penta, hepta and deca coupled layers which have been characterized for their optical properties using photoluminescence spectroscopy (PL) and photoluminescence excitation spectroscopy measurements (PLE) while high resolution X-ray diffraction (HR-XRD) measurements (in-plane and out-of-plane) have been carried out for structural characterization. A gradual shift from bi-modal to monomodal distribution is observed on increasing the coupled layers above five. Activation energies (Ea) calculated from temperature dependent PL results show least thermal quenching for hepta layer coupling which is further corroborated by the strongest room temperature luminescence obtained for the respective sample amongst others. Least out-of-plane compressive strain and also least in-plane tensile strain have been calculated from the HR-XRD results for the hepta layer coupled sample. Furthermore, the in-plane HR-XRD results show minimal amount of In–Ga intermixing for the hepta layer coupling which provides direct evidence of the superior material quality of this heterostructure. Quantum-dot infrared photodetectors (QDIPs) fabricated from the samples have been characterized for their spectral response wherein multiple sharp peaks with narrow full-width at half maxima (FWHM) are obtained in the short-wave infrared (SWIR) region for the hepta layer device, which is absent in other spectra. Also, the response survives up to room temperature (300 K) and stretches in the mid-wave infrared region (MWIR) region (~5 μm). High peak responsivity (Rp = 120.34 A/W) is obtained for the hepta layer device which is much higher than previously reported responsivity values.

Quantum dot based mid-infrared photodetector enhanced by a hybrid metal-dielectric optical antenna

Surface plasmon waves and Rayleigh anomaly are characteristic optical phenomena exhibited by periodic subwavelength grating structures. In this paper, a hybrid metal-dielectric metasurface is proposed to improve the photoresponse of Ge/Si quantum dot infrared photodetectors (QDIPs) with limited absorption layer thickness. The composite metasurface consists of a regular array of silicon pillars. The pillars protrude through subwavelength holes in a perforated gold film on the detector top. We demonstrate that by combining effects of dielectric and plasmonic metal components, the QDIP photoresponse can be significantly improved compared to case when all-dielectric and metal gratings work alone. We observe about four times photoresponse enhancement with the hybrid metasurface device relative to a common plasmonic design with a two-dimensional metal hole array. Compared with a bare QDIP, the peak responsivity of the hybrid detector at a wavelength of 4.4 µm is increased by a factor of 15. The enhanced sensitivity is supposed to arise from coupling of the surface plasmon resonance and diffractive effect related to the Rayleigh anomaly.

Enhanced Absorptivity of Quantum Dot Infrared Photodetector by Introducing of Metal Nanostructure Layer

Quantum dot infrared photodetector (QDIP) shows more superior characteristics; however, the low absorption rate is still the fundamental factor restricting the performance of the detector. So in our paper, the QDIP is improved by introducing the metal structure with the strips and holes to increase absorptivity. The results demonstrate that the enhanced QDIP can greatly improve the photon absorptivity up to 98.92% as a result of the local coupling surface plasmon effect, which is 1.23 times than that of the conventional photodetectors without the metal array structures.

Multispectral imaging of mineral samples by infrared quantum dot focal plane array sensors

Abstract Infrared (IR) spectral imaging is a powerful tool for component analysis and identification in the geological field. In this report, we originally use quantum dot infrared photodetector (QDIP) focal plane arrays (FPAs) with different peak-responsivity wavelengths to analyze the mineral composition of rock samples by IR spectral imaging and show the QDIP’s potential as a solution for some geological problems. After clarifying fundamental characteristics such as the blackbody responsivity, current noise density, and spectral responsivity of QDIPs, we present qualitative and quantitative analyses of mineral samples including conglomerate, sandstone, marble, and dolomite. In the qualitative analysis, we distinguish two different compositions in each rock. In the quantitative analysis, we measure the emittance of dolomite and show the emittance errors. Finally, we discuss which experimental factor determines the quantitative precision most dominantly.

Quantum efficiency of plasmonic-coupled quantum dot infrared photodetectors for single- color detection: the upper limit of plasmonic enhancement

We report a measurement of the quantum efficiency for a surface plasma wave (SPW)-coupled InAs/In0.15Ga0.85As/GaAs dots-in-a-well (Dwell) quantum dot infrared photodetector (QDIP) having a single-color response at ∼10 µm. A gold film perforated with a square array of complex, non-circular apertures is employed to manipulate the near-fields of the fundamental SPW. The quantum efficiency is quantitatively divided into absorption efficiency strongly enhanced by the SPW, and collection efficiency mostly independent of it. In the absorption efficiency, the evanescent near-fields of the fundamental SPW critically enhances QDIP performance but undergoes the attenuation by the absorption in the Dwell that ultimately limits the quantum efficiency. For the highest quantum efficiency available with plasmonic coupling, an optimal overlap between Dwell and SPW near-fields is required. Based on experiment and simulation, the upper limit of the plasmonic enhancement in quantum efficiency for the present device is addressed.

Modeling of carrier mobility for semispherical quantum dot infrared photodetectors (QDIPs)

Carrier mobility for quantum dot infrared photodetectors is considered as one of the critical parameters to determine many important device’s performance parameters such as the electrical conductivity, drift velocity, dark current and photocurrent. In this paper a complete theoretical model of the carrier mobility for semispherical quantum dot structures is developed. This model is based on the solution of Boltzmann transport equation all over the device. A parametric study of the effects of the QD density and the dimensions of the QD on the carrier mobility is investigated. Finally, the carrier mobility in semispherical QDIP is compared with other QD structures. The presented model is a generic model that can be applied for different semispherical QD structures.

Theoretical correlation and effect of annealing on the photoresponse of vertically strain-coupled In0.5Ga0.5As/GaAs quantum dot heterostructures

Here, we propose a different approach for growing strain-coupled In0.5Ga0.5As quantum dot infrared photodetectors (QDIPs) with varying dot layer periodicity. Strain calculation is done throughout the quantum dot (QD) heterostructures, which has a significant effect on the carrier probability density functions. The localization of the electron probability density function in each heterostructure has a strong correlation with the photoresponse. The confined electron wavefunction in the top QD layer of the optimized device heterostructure (trilayer QDIP having dot layer periodicity of three) would be useful for hyperspectral imaging applications owing to its narrow (8.67 meV) photoresponse. Rapid thermal annealing treatment was carried out on the trilayer QDIP to investigate the enhancement in its optoelectronic properties. The dark current density reduced by two orders, and the operating temperature increased by 30 °C for the 650 °C-annealed counterpart. Also, the responsivity enhanced by two times (2.05 A/W at −1 V) for the annealed QDIP.

Spatial Optimization of Modulation Doping in P-I-P QDIPs: Towards Achieving Higher Operating Temperature

We report short wavelength infrared (SWIR) photodetectors using multi-stacked modulation doped Indium-Arsenide (InAs) self-assembled quantum dots (QDs). The detriments of direct doping on the energy levels of InAs QDs have been eliminated by choosing modulation doping. We have considered three P-I-P Indium Arsenide/Gallium Arsenide (InAs/GaAs) quantum dot infrared photodetector (QDIP) heterostructures in which a thin (3 nm) P-doped GaAs layer is introduced at a distance of 7, 12 and 17 nm away from each InAs dot layer respectively. The structures have been analyzed for their morphological and optical characteristics and an optimum separation between the active layer and modulation doped layer has been achieved. The fabricated single pixel detectors exhibit a broad spectral response from 1 to 3.5 μm in the SWIR region for all the samples. The infrared photocurrent survives up to a maximum temperature of 200K for the optimized device with a peak responsivity of 1.439 A/W at wavelength λ = 1.77 μm and temperature T = 200 K.

Effect of Si Doping in Self-Assembled InAs Quantum Dots on Infrared Photodetector Properties

We investigate the characteristics of self-assembled quantum dot infrared photodetectors(QDIPs) based on doping level. Two kinds of QDIP samples are prepared using molecular beam epitaxy : n+-i(QD)-n+ QDIP with undoped quantum dot(QD) active region and n+-n−(QD)-n+ QDIP containing Si direct doped QDs. InAs QDIPs were grown on semi-insulating GaAs (100) wafers by molecular-beam epitaxy. Both top and bottom contact GaAs layer are Si doped at 2×1018/cm3. The QD layers are grown by two-monolayer of InAs deposition and capped by InGaAs layer. For the n+-n−(QD)-n+ structure, Si dopant is directly doped in InAs QD at 2×1017/cm3. Undoped and doped QDIPs show a photoresponse peak at about 8.3 μm, ranging from 6~10 μm at 10 K. The intensity of the doped QDIP photoresponse is higher than that of the undoped QDIP on same temperature. Undoped QDIP yields a photoresponse of up to 50 K, whereas doped QDIP has a response of up to 30 K only. This result suggests that the doping level of QDs should be appropriately determined by compromising between photoresponsivity and operating temperature.

Temperature Dependence of Quantum Dots-In-Well Infrared Photo Detectors (QDIPs) using Photoluminescence

A research of quantity dots-in-well infrared photo detectors (QDIPs) produces helpful outcomes for creating a twocolor QDIP. Quantum dot infrared photo detectors (QDIPs) have been shown to be a main technology in mid-and longwavelength infrared detection owing to their capacity for normal incidence operation and low dark current. This research explores infrared detectors based on intersubband transitions in a novel heterostructure of InAs / In0.15 Ga0.85 As / GaAs quantum dotsin-well (DWELL). The InAs quantum dots are also positioned in an In0.15 Ga0.85 in the DWELL framework, which in turn is well positioned with the In0.1Ga0.9As obstacle in GaAs quantum. Using fourier transform infrared spectroscopy, the optical characteristics of the sample were researched using photoluminescence and photocurrent. Spectrally adjustable reaction was noted at 6.2μm and 7.5μm with prejudice and lengthy wave IR reaction

Microcavity Effect in InAs/GaAs Quantum Dot Infrared Photodetector on a Si Substrate Fabricated With Metal Wafer Bonding and Epitaxial Lift-Off Techniques

In this paper, the microcavity effect in quantum dot infrared photodetectors (QDIPs) on a Si substrate, fabricated by means of metal wafer bonding (MWB) and epitaxial lift-off (ELO) processes, was demonstrated by comparing the photocurrent spectrum and the simulated absorption spectrum. Four QDIPs having a different cavity length of 1.7, 2.8, 3, and 3.4 μm were fabricated and compared with simulation based on the finite-difference time-domain method. The resonance peaks were observed in both photocurrent spectrum and absorption spectrum due to the microcavity formed by the bottom mirror of Pt/Au layer and the flat GaAs/air interface. The peak wavelength of the photocurrent spectrum in all four QDIPs on Si samples shows a good agreement with the simulated absorption spectrum. The bias-dependent photocurrent was also measured to study the microcavity effects more in depth. The ratio of the increased photocurrent under bias condition shows higher value in the microcavity QDIPs, showing that the microcavity contributes to generate photocurrent effectively. From these results, we believe that the MWB and ELO could be useful to make the microcavity in many integrated chemical and biosensing application.