Dots-in-a-well Research Articles

Impact of composition of AlGaInAs confining barriers on emission of InAs quantum dots embedded in AlGaAs/GaAs dot-in-a-well heterostructures

The emission of InAs quantum dots (QDs) grown on Al0.30 Ga0.70As/GaAs heterostructures and integrated into additional capping/buffer quantum wells (QW), known as dot-in-a-well (DWELL) structures, has been investigated. Two different AlGaInAs confining barriers (CBs) and buffer layers (BLs) are compared. The first QD structure includes the Al0.30 Ga0.70As CB (#1) and the In0.15Ga0.85As BL. The second QD structure consists of the Al0.40Ga0.45In0.15As CB (#2) and the In0.25Ga0.75As BL. Comparison of photoluminescence (PL) spectra has revealed that the ground state (GS) emission band in the structure #2 with Al0.40Ga0.45In0.15As CB is characterized by the lower peak energy, smaller PL linewidth (more homogeneous QD sizes) and higher GS emission intensity compared to that parameters in the structure #1 with Al0.30 Ga0.70As CB. The smaller potential barriers at the Al0.40Ga0.45In0.15As CB/QD interfaces in #2 lead to faster thermal decrease in the GS PL intensity at high temperatures compared with that in #1. High-resolution X-ray diffraction (HR-XRD) method was used for the study of the QD structures with the aim of monitoring the sizes and compositions of QDs and QWs. Numerical simulation of HR-XRD scans has shown that the material compositions of QDs and QW in #2 with Al0.40Ga0.45In0.15As CB has not changed in the process of QD structure growth at high temperatures compared to those in #1. The obtained results are interesting for further improvement of InAs/GaAs QD structures for telecommunication technology and optoelectronic applications.

In segregation influence on properties of InAs quantum dots in dots-in-a-well

We investigated the growth of InAs quantum dots (QDs) in a dots-in-a-well (DWELL) from the perspective of the influence of In segregation from the InGaAs layers in the DWELL. Reflection high-energy electron diffraction (RHEED) measurements during the growth of the lower InGaAs layer indicated that In segregation increased with the In composition of the InGaAs layer. The estimated In segregation values were consistent with the decreases in the critical thickness for the QDs growth and the total volume variations of the grown QDs. These results illustrate that the segregated In from the lower InGaAs layer contributes to the QD growth in the DWELL, and their density increases. Furthermore, RHEED measurements during the growth of the upper InGaAs layer indicated the suppression of the deformation of embedded QDs , which could partially contribute to the longer emission wavelength of the QDs in the DWELL.

InAs quantum dot-in-a-well heterostructures with InGaAs, GaAsN and GaAsSb well using digital alloy capping layer

In this work, the authors introduced a novel approach called digital alloy capping layer (DACL) and investigated its effect on the optical and structural properties of InAs quantum dot-in-a-well (DWELL) heterostructures. In DACL, a conventional thick well layer is digitized equally with different compositions analogous to short-period-superlattice (SPS). The DACL approach's effect has been studied experimentally and theoretically on DWELL heterostructures with InxGa1-xAs as the well material. The photoluminescence (PL) study reveals that DACL observes a red-shift of ∼55 nm as compared to AACL approached heterostructures. High-resolution X-ray diffraction (HRXRD) results reveal higher In-content, controlled In-out diffusion from InAs QD, and improved in-plane strain in DACL samples compared to the analog sample. The study has been extended to QD heterostructures with GaAs1-xNx and GaAs1-ySby as well materials, and comprehensive analysis has been carried out. Hence, the DWELL heterostructures with the DACL approach can be utilized to fabricate infrared photodetector devices.

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.

Plasmonic-Layered InAs/InGaAs Quantum-Dots-in-a-Well Pixel Detector for Spectral-Shaping and Photocurrent Enhancement.

The algorithmic spectrometry as an alternative to traditional approaches has the potential to become the next generation of infrared (IR) spectral sensing technology, which is free of physical optical filters, and only a very small number of data are required from the IR detector. A key requirement is that the detector spectral responses must be engineered to create an optimal basis that efficiently synthesizes spectral information. Light manipulation through metal perforated with a two-dimensional square array of subwavelength holes provides remarkable opportunities to harness the detector response in a way that is incorporated into the detector. Instead of previous experimental efforts mainly focusing on the change over the resonance wavelength by tuning the geometrical parameters of the plasmonic layer, we experimentally and numerically demonstrate the capability for the control over the shape of bias-tunable response spectra using a fixed plasmonic structure as well as the detector sensitivity improvement, which is enabled by the anisotropic dielectric constants of the quantum dots-in-a-well (DWELL) absorber and the presence of electric field along the growth direction. Our work will pave the way for the development of an intelligent IR detector, which is capable of direct viewing of spectral information without utilizing any intervening the spectral filters.

Comparison of carrier localization effects between InAs quantum dashes and quantum dots in a DWELL (dashes- or dots-in-a-well) configuration

The optical properties of InAs quantum dashes (QDashes) grown on InP and InAs quantum dots (QDots) grown on GaAs in a dashes- or dots-in-a-well (DWELL) configuration are comparatively investigated using temperature-dependent photoluminescence (PL) measurements. The trends in PL characteristics such as exciton energy, spectral bandwidth and integrated intensity with respect to temperature are found to be distinctly dissimilar between the two systems. A rate-equation model involving exciton recombination and thermal transfer in a localized-state ensemble is used to quantitively interpret the experimental data. These results suggest that QDashes in this configuration exhibit PL properties more consistent with a lower degree of carrier localization compared to QDots. A preliminary structural analysis highlighting the shape/size differences between the two nanostructures is also presented.

Optimizing dot-in-a-well infrared detector architecture for achieving high optical and device efficiency corroborated with theoretically simulated model

Dot-in-a-well (DWELL) heterostructures have been extensively researched in quantum dot based infrared photo-detectors as it offers tuning of detection peak wavelength, low dark current and a higher operating temperature with optimized quantum well thickness. In this paper, we have correlated experimentally observed opto-electronic properties of three different InAs quantum dots in DWELL configuration with varying ternary capping (In0.15Ga0.85As - Strain reducing ternary alloy) thickness from 4 to 8 nm to the proposed simulation model for achieving high efficiency in device performance. Low temperature (8 K) photoluminescence (PL) spectra exhibits a blue shift of around 24 nm along with a decrease in intensity as the capping thickness increases above 6 nm. Decrease in full width at half maximum (FWHM) value for PL peak was observed as the capping thickness is increased from 6 to 8 nm. These are attributed to formation of InGaAs quantum wells via dots sublimation process. Presence of InGaAs wells for 8 nm capped sample was confirmed using low temperature photoluminescence measurement at 2.54 W/cm2 and photoluminescence excitation (PLE). Time resolved photoluminescence spectroscopy gave further insight into the carrier dynamics of the grown structures and confirms undesirable quantum well formation in 8 nm capped sample. Improved optical characteristics with formation of defect-free structure having larger quantum dot was achieved in 6 nm capped sample affirmed using transmission electron microscopy images. Low dark current density with high confinement energy was achieved from 6 nm capped DWELL structure. Dominant spectral response peak was obtained at 7.56 μm from all the samples. A concentration-dependent theoretical strain model using the Schrödinger equation was developed to calculate the potential, ground-state and inter-sub band energy-levels. It was validated by comparing experimentally achieved PL and PLE peaks along with spectral response peaks. The theoretical model was used to calculate the energy levels corresponding to conduction and valence bands for InGaAs well and indium concentration in the well was obtained to be around 30%. Similarly, concentration dependent 2D to 3D transition for InxGa1-xAs (0 ≤ x ≤ 1) quantum dots formation was modelled using People-Bean relation which matches with the proposed simulation.

Demonstration of InAs/InGaAs/GaAs Quantum Dots-in-a-Well Mid-Wave Infrared Photodetectors Grown on Silicon Substrate

In this paper, we have demonstrated the first InAs/InGaAs/GaAs quantum dots-in-a-well (DWELL) photodetector monolithically grown on silicon substrate. We studied both the optical and electrical characteristics of the DWELL photodetectors. Time-resolved photoluminescence spectra measured from the DWELL photodetector revealed a long carrier lifetime of 1.52 ns. A low dark current density of ${\text{2.03}}\times {\text{10}}^{-3}\;{\text{mA/cm}}^{2}$ was achieved under 1 V bias at 77 K. The device showed a peak responsivity of 10.9 mA/W under 2 V bias at the wavelength of 6.4 μ m at 77 K, and the corresponding detectivity was ${\text{5.78}}\times {\text{10}}^{8}\,{{\text{cm}\cdot \text{Hz}}}^{1/2}{\text{/W}}$ . These results demonstrated that these silicon-based DWELL photodetectors are very promising for future mid-infrared applications, which can enjoy the potential benefit from mid-infrared silicon photonics technology.

Optically pumped lasing in a rolled-up dot-in-a-well (DWELL) microtube via the support of Au pad

We report the observation of optically pumped continuous wave lasing in a self-rolled-up InGaAs/GaAs quantum dot microtube at room temperature. Single layer of InAs quantum dots (~ 2.6 ML coverage) in a GaAs well sandwiched by two AlGaAs barriers are incorporated into the tube wall as the gain media. As-fabricated microtube is supported by a 300-nm-thick Au pad, aiming to separate the tube from GaAs substrate and thus to decrease the substrate loss, which finally enables lasing with ultralow threshold power (~ 4 µW) from an microtube ring resonator.

Ultrathin GaAsN matrix-induced reduced full width at half maximum of GaAsN/InAs/GaAsN dot-in-a-well heterostructures with extended emission wavelength

We grew InAs quantum dots (QDs) embedded in a GaAs0982N0.018 quantum well—a dot-in-a-well (DWELL) structure—that exhibits emission at wavelengths of up to 1.31µm at 19K and the full width at half maximum (FWHM) of 59meV which are lower those of the InAs/GaAs QDs (1.09µm and 82meV, respectively), the reference sample. Our results can be explained as follows: modified strain field at the GaAsN matrix/InAs QDs due to insertion of ultrathin GaAsN matrix, or nitrogen-induced point defects formed in the ultrathin GaAsN matrix during growth, could promote the homogeneous distribution of InAs QDs on the surface. The GaAsN capping layer evidently enhances the emission wavelength by reducing the overall compressive strain within the QDs. DWELL with ultrathin matrix layer annealed at 800°C exhibited 130-fold improvement in PL intensity, as compared to the as-grown sample, attributed to annihilation of N-related point defects. The results of this study are expected to be useful in fabricating DWELL-based infrared photodetectors with narrow spectral linewidth.

Noise, gain, and capture probability of p-type InAs-GaAs quantum-dot and quantum dot-in-well infrared photodetectors

We report experimental results showing how the noise in a Quantum-Dot Infrared photodetector (QDIP) and Quantum Dot-in-a-well (DWELL) varies with the electric field and temperature. At lower temperatures (below ∼100 K), the noise current of both types of detectors is dominated by generation-recombination (G-R) noise which is consistent with a mechanism of fluctuations driven by the electric field and thermal noise. The noise gain, capture probability, and carrier life time for bound-to-continuum or quasi-bound transitions in DWELL and QDIP structures are discussed. The capture probability of DWELL is found to be more than two times higher than the corresponding QDIP. Based on the analysis, structural parameters such as the numbers of active layers, the surface density of QDs, and the carrier capture or relaxation rate, type of material, and electric field are some of the optimization parameters identified to improve the gain of devices.

RADIATION PERFORMANCE OF GAN AND INAS/GAAS QUANTUM DOT BASED DEVICES SUBJECTED TO NEUTRON RADIATION

In addition to their useful optoelectronics functions, gallium nitride (GaN) and quantum dots (QDs) based structures are also known for their radiation hardness properties. With demands on such semiconductor material structures, it is important to investigate the differences in reliability and radiation hardness properties of these two devices. For this purpose, three sets of GaN light-emitting diode (LED) and InAs/GaAs dot-in-a well (DWELL) samples were irradiated with thermal neutron of fluence ranging from 3×1013 to 6×1014 neutron/cm2 in PUSPATI TRIGA research reactor. The radiation performances for each device were evaluated based on the current-voltage (I-V) and capacitance-voltage (C-V) electrical characterisation method. Results suggested that the GaN based sample is less susceptible to electrical changes due to the thermal neutron radiation effects compared to the QD based sample.

Fabrication and characterization of InAs/InGaAs sub-monolayer quantum dot solar cell with dot-in-a-well structure

To improve the efficiency of InAs quantum dot solar cells (QDSCs), we propose a QDSC structure with sub-monolayer (SML) QDs. The optical and electrical properties of Stranski–Krastanow (SK) QDs and SML-QDs embedded in dot-in-a-well (DWELL) were investigated by photoluminescence and photoreflectance spectroscopy and illuminated J-V measurement. The SML-QDSC showed the improved probability of carriers thermally escaping from the QD states due to the small QD size. The suppression of carrier re-capturing enhanced the photovoltaic effect due to the enhanced carrier screening. The conversion efficiency of the SML-QDSC (η = 10.65%) was enhanced by about 12.58% compared to that of the SK-QDSC (η = 9.46%). The improved SC efficiency of the SML-QD is attributed to the suppressed carrier re-capturing and carrier trapping caused by the smaller QD size and lower defect density.

Neutron Radiation Effects on the Electrical Characteristics of InAs/GaAs Quantum Dot-in-a-Well Structures

This paper studies the effects of neutron radiation on the electrical behaviour and leakage current mechanism of quantum dot-in-a-well (DWELL) semiconductor diodes with fluence ranging from 3 to $9 \times 10^{13}~\hbox{neutron/cm}^{2}$ . After neutron irradiation, the forward bias and reverse bias leakage currents showed significant rise approximately of up to two orders of magnitude which is believed to be attributed to the presence of displacement damage induced traps. The ideality factor of the forward bias leakage current corresponding to all neutron fluence irradiations were found to be close to 2, suggesting that the forward bias current mechanism is largely due to trap-assisted generation-recombination (TAGR) of carriers. Subsequently, it is also observed that the capacitances reduced after irradiations which were further shown to be due to the deep carrier trapping effects and the Neutron Transmutation Doping effects (NTD). From the temperature dependence measurements, it is found that the reverse bias leakage current mechanisms of the irradiated samples are primarily attributed to two process; TAGR of carriers with emission from the traps assisted by the Frenkel-Poole (F-P). The traps due to both mechanisms were derived and shown to increase with neutron fluence.

Investigation of the electrical and optical properties of InAs/InGaAs dot in a well solar cell

The electroreflectance (ER) and current–voltage (J–V) of InAs/InGaAs dots in a well (DWELL) solar cell (SC) were measured to examine the optical and electrical properties. To investigate the carrier capturing and escaping effects in the quantum dot (QD) states the above and below optical biases of the GaAs band gap were used. In the reverse bias region of the J–V curve, the tunneling effect in the QD states was observed at low temperature. The ideality factors (n) were calculated from the J–V curves taken from various optical bias intensities (Iex). The changes in the ideality factor (n) and short circuit current (JSC) were attributed mainly to carrier capture at low temperature, whereas the carrier escaping effect was dominant at room temperature. ER measurements revealed a decrease in the junction electric field (FJ) due to the photovoltaic effect, which was independent of the optical bias source at the same temperature. At low temperature, the reduction of photovoltaic effect could be explained by the enhancement carrier capturing effect due to the strong carrier confinement in QDs.

Comparison of Three Design Architectures for Quantum Dot Infrared Photodetectors: InGaAs-Capped Dots, Dots-in-a-Well, and Submonolayer Quantum Dots

In this letter, we compare three design architectures for quantum dot infrared photodetectors—InGaAs-capped InAs dots, InAs dot-in-a-well (DWELL), and InAs submonolayer (SML) heterostructures—in terms of optical and spectral behavior. The photoluminescence (PL) intensity measured of the SML sample at 8 K was 20 times stronger than that of the other samples, and its full-width at half-maximum value broader than the rest. Activation energy was calculated using temperature-dependent PL and dark current measurements, which showed the same trend. Peak spectral responses for the InGaAs-capped InAs dot and DWELL samples were observed at 4.1 and 7.3 μm and at 4.1 and 8.5 μm, respectively; however, only a single transition was observed for the SML sample because of the absence of a wetting layer. Spectral response of DWELL sample exhibited bias tunability at 87 K, and the SML sample exhibited high temperature of operation till 110 K. One order increment in responsivity was observed in the SML sample compared to others. The peak detectivity of InGaAs-capped InAs dot, DWELL, and SML samples was $4.1 \times 10^{9}$ , $4.99 \times 10^{9}$ , and $3.89 \times 10^{9}$ Jones, respectively, at 87 K.

High temperature terahertz response in a p-type quantum dot-in-well photodetector

Terahertz (THz) response observed in a p-type InAs/In0.15Ga0.85As/GaAs quantum dots-in-a-well (DWELL) photodetector is reported. This detector displays expected mid-infrared response (from ∼3 to ∼10 μm) at temperatures below ∼100 K, while strong THz responses up to ∼4.28 THz is observed at higher temperatures (∼100–130 K). Responsivity and specific detectivity at 9.2 THz (32.6 μm) under applied bias of −0.4 V at 130 K are ∼0.3 mA/W and ∼1.4 × 106 Jones, respectively. Our results demonstrate the potential use of p-type DWELL in developing high operating temperature THz devices.

Investigation on the lasing characteristics of InAs/InGaAsP quantum dots with additional confinement structures

We report on morphological, optical, and lasing characteristics of InAs quantum dots (QDs) embedded in an In0.69Ga0.31As0.67P0.33 quantum well (having a bandgap energy corresponding to a wavelength of 1.35μm (1.35Q-InGaAsP)), which formed a dot-in-a-well (DWELL) structure. This DWELL was further sandwiched in In0.85Ga0.15As0.32P0.68 layers (1.15μm, 1.15Q-InGaAsP). A 2 monolayer-thick GaAs layer was simultaneously introduced right below the InAs QD layer in the DWELL structure (GDWELL). The emission wavelength of the InAs GDWELL was 1490nm, which was slightly shorter than that of the InAs QDs embedded only in 1.15Q-InGaAsP layers. To evaluate the effects of the GDWELL structure on lasing characteristics, gain-guided broad-area (BA) and index-guided ridge-waveguide (RW) laser diodes (LDs) were fabricated. The BA-LDs with the InAs QDs embedded only in 1.15Q-InGaAsP layers did not show the lasing at room temperature (RT) even in pulsed mode. For the GDWELL structure, however, the lasing emissions from both the BA-LDs and RW-LDs were successfully achieved at RT in continuous-wave mode.

Numerical analysis on quantum dots-in-a-well structures by finite difference method

A finite difference technology is applied to the InAs/InGaAs/GaAs quantum dots-in-a-well (DWELL) structures in order to determine their electronic properties. Conventional quantum dots (QDs) sample has a simple structure, i.e., the QDs are imbedded in a GaAs bulk medium. In stead of the conventional structure, we prefer the weak confinement DWELL structure because it can efficiently lower the intersubband transition energy. Thus the DWELL detector is expected to make the longer wavelength detection possible. Present method used in this study is demonstrated to be efficient and flexible for determining the electronic state of the DWELL system. However, to our knowledge there has been no literature reporting so far on the electronic structure of DWELL characterized by the finite difference method.

NAnalysis of subwavelength metal hole array structure for the enhancement of back-illuminated quantum dot infrared photodetectors

This paper is focused on analyzing the impact of a two-dimensional metal hole array structure integrated to the back-illuminated quantum dots-in-a-well (DWELL) infrared photodetectors. The metal hole array consisting of subwavelength-circular holes penetrating gold layer (2D-Au-CHA) provides the enhanced responsivity of DWELL infrared photodetector at certain wavelengths. The performance of 2D-Au-CHA is investigated by calculating the absorption of active layer in the DWELL structure using a finite integration technique. Simulation results show that the performance of the DWELL focal plane array (FPA) is improved by enhancing the coupling to active layer via local field engineering resulting from a surface plasmon polariton mode and a guided Fabry-Perot mode. Simulation method accomplished in this paper provides a generalized approach to optimize the design of any type of couplers integrated to infrared photodetectors. Experimental results demonstrate the enhanced signal-to-noise ratio by the 2D-Au-CHA integrated FPA as compared to the DWELL FPA. A comparison between the experiment and the simulation shows a good agreement.