InAs QDs Research Articles

Hydrogen chloride treated InAs quantum dot thin film phototransistor for ultrahigh responsivity

Indium Arsenide (InAs) colloidal quantum dots (CQDs) are emerging candidates for infrared photodetector applications owing to their excellent optoelectronic properties and low toxicity. However, low electron mobility stemming from its unique surface chemistry hinders its practical application. Through comprehensive structural and chemical analyses, we optimized the one-step HCl treatment to achieve stoichiometric balance, a well-passivated surface with low defect density, and an improved coupling effect by reducing the interparticle distance. Subsequently, a near infrared photodetector at a wavelength of 980 nm was fabricated with the modified InAs QDs in thin film transistor structure by all-solution process, showing remarkable electron mobility enhancement of up to 3.15 cm2/V∙s. The thin film phototransistor exhibited excellent photoresponse with a responsivity of 5.45 × 103 A/W, external quantum efficiency of 6.90 × 105%, and a linear dynamic range of 50 dB. This achievement represents the highest responsivity observed in an InAs QD-based phototransistor device, demonstrating its potential for lead-free infrared (IR) region optoelectronic applications.

Research on the assessment of technical methods to suppress auger recombination

Human demand for fossil fuels has reached a very high level. However, fossil energy stocks are limited and, more importantly, their impact on the environment is increasing. The exploration of clean energy is particularly important. Among all the clean energy sources, solar energy is a very promising and important alternative to fossil fuels. And one of the primary reasons for the failure of solar photovoltaic cells to achieve rapid development is the generation of Auger composite. In order to provide support to solve this problem or facilitate the follow-up of researchers, this paper summarizes several effective methods such as Interfacial Engineering and Gradient Alloying to solve the Auger recombination problem in multi-exciton photovoltaic cells through reading and comparing a large number of relevant authoritative literature. The two methods mentioned above suppress Auger recombination by applying a new type of MXene (Nb2CTX-MXene) to the interface of SnO2 layers to pssivate the interfacial defects and promote charge transport and to generate InAs/CdSe core/shell QDs, overcoating InAs QDs with a lattice-matched CdSe shell. Comparing a large number of pieces of literature, it is found that the above two methods have guiding effects in improving the efficiency of photovoltaic cells.

Exploring the Implementation of GaAsBi Alloys as Strain-Reducing Layers in InAs/GaAs Quantum Dots.

This paper investigates the effect of GaAsBi strain reduction layers (SRLs) on InAs QDs with different Bi fluxes to achieve nanostructures with improved temperature stability. The SRLs are grown at a lower temperature (370 °C) than the usual capping temperature for InAs QDs (510 °C). The study finds that GaAs capping at low temperatures reduces QD decomposition and leads to larger pyramidal dots but also increases the threading dislocation (TD) density. When adding Bi to the capping layer, a significant reduction in TD density is observed, but unexpected structural changes also occur. Increasing the Bi flux does not increase the Bi content but rather the layer thickness. The maximum Bi content for all layers is 2.4%. A higher Bi flux causes earlier Bi incorporation, along with the formation of an additional InGaAs layer above the GaAsBi layer due to In segregation from QD erosion. Additionally, the implementation of GaAsBi SRLs results in smaller dots due to enhanced QD decomposition, which is contrary to the expected function of an SRL. No droplets were detected on the surface of any sample, but we did observe regions of horizontal nanowires within the epilayers for the Bi-rich samples, indicating nanoparticle formation.

Lattice‐Mismatched Epitaxy of InAs on (111)A‐Oriented Substrate: Metamorphic Layer Growth and Self‐Assembly of Quantum Dots

In this article, recent developments in the lattice‐mismatched epitaxy of InAs on (111)A‐oriented substrates and related research topics, in which the presence or absence of the misfit dislocations is controlled via prescribed growth sequences, are reviewed. When InAs is grown on GaAs (111)A substrates, a unique lattice‐relaxation mechanism occurs. A misfit dislocation network is formed at the initial stage of InAs growth, that is followed by the layer‐by‐layer growth of relaxed InAs films. The InAs/GaAs (111)A heterostructure is being applied in infrared photodetectors which have a new operating principle that employs the high‐density dislocations at the interface. The InAs/GaAs (111)A heterostructure is also useful for the growth of InGaAs layers: a nearly lattice‐relaxed InGaAs containing different concentrations of indium can be formed by inserting a thin‐InAs layer between the InGaAs and GaAs. These InGaAs layers can be used as virtual substrates with a desired lattice constant for a range of devices. In addition to the formation of lattice‐relaxed structures, dislocation‐free InAs quantum dots (QDs) can be formed on InP (111)A substrates by applying droplet epitaxy. The C3v symmetry of the (111)A surface makes it possible to form symmetric InAs QDs that emit entangled photon pairs at telecommunication wavelengths.

Formation of strain reduced In0.54Al0.34Ga0.12As layer of vertically coupled QDs arrays for O-band telecom single photon sources

We demonstrate the correlative research on the multi-stacked vertically coupled InAs quantum dots (VCQDs) capped by 15 nm combinational capping layer of In(0.21)Al(0.21)Ga(0.58)As and GaAs layer through Atom probe tomography (APT), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectroscopy (SIMS), High-Resolution X-Ray Diffraction (HRXRD) and Reciprocal Space Mapping (RSM). From the comparative studies, we observed a strain reduction of ∼ 2.3 ± 0.05% in the system, leading to the formation of strain-reduced (SR) In0.54Al0.34Ga0.12As layer with a lattice constant of 5.88 Å, which will work as a shielding layer. We found that the middle portion of the 3rd to 8th layer QDs structure was constant in size, shape, composition, and density, which enhances the carrier confinement in QDs. The computed strain energy values contributed to the overall growth structure of the 30 - layers VCQDs were recorded to be 2.2 meV/atoms. We report the detailed analogy of the in-out flow of In/Ga adatoms in the In0.54Al0.34Ga0.12As layer leading to the evolution of fully developed bigger InAs QDs size. To support the APT results, we also present the outcomes studies of the HRXRD Out-plane and In-Plane symmetric RSM experiment at (002), (004), and (006) reflections to investigate the compressive strain contribution in the SR In0.54Al0.34Ga0.12As shielding layer. This 30-layer VCQDs structure can be employed to fabricate high thermal stability operating at 1.3 µm O-band telecom Single Photon Sources (SPSs).

Effects of High-Temperature Growth of Dislocation Filter Layers in GaAs-on-Si

GaAs-on-Si templates with two different dislocation filter layers (DFLs) were grown at 550 °C low-temperature (LT)-DFL and 660 °C high-temperature (HT)-DFL using metal organic vapor-phase epitaxy and the effects of the growth temperature were studied. The threading dislocation density (TDD) values of LT-DFL and HT-DFL were 5.2 × 107 cm−2 and 1.5 × 107 cm−2, respectively. The 1.5 × 107 cm−2 of TDD in HT-DFL is reduced by almost one order compared to the 1.2 × 108 cm−2 of that in the control sample without DFLs. The annihilation process was mainly observed in the HT-DFL by a transmission electron microscope, resulting in a lower TDD. The 500-nm-thick GaAs bulk layer and InAs QDs were regrown on GaAs-on-Si templates and the optical properties were also evaluated by photoluminescence (PL). The highest PL peak intensity of the HT-DFL indicates that less non-radiative recombination in both the GaAs bulk and QDs occurred due to the reduced TDD. The GaAs p–i–n diodes were also fabricated to analyze the bulk leakage (JB) and the surface leakage current. The JB of HT-DFL shows the lowest value of 3.625 × 10–7 A/cm−2 at applied bias voltage of 1 V, which is 20 times lower than the JB of the control sample without DFLs. This supports that the high-temperature growth of DFL can make a good performance GaAs device on Si.

Reduced Dislocation of GaAs Layer Grown on Ge-Buffered Si (001) Substrate Using Dislocation Filter Layers for an O-Band InAs/GaAs Quantum Dot Narrow-Ridge Laser.

The development of the low dislocation density of the Si-based GaAs buffer is considered the key technical route for realizing InAs/GaAs quantum dot lasers for photonic integrated circuits. To prepare the high-quality GaAs layer on the Si substrate, we employed an engineered Ge-buffer on Si, used thermal cycle annealing, and introduced filtering layers, e.g., strained-layer superlattices, to control/reduce the threading dislocation density in the active part of the laser. In this way, a low defect density of 2.9 × 107 cm−2 could be achieved in the GaAs layer with a surface roughness of 1.01 nm. Transmission electron microscopy has been applied to study the effect of cycling, annealing, and filtering layers for blocking or bending threading-dislocation into the InAs QDs active region of the laser. In addition, the dependence of optical properties of InAs QDs on the growth temperature was also investigated. The results show that a density of 3.4 × 1010 InAs quantum dots could be grown at 450 °C, and the photoluminescence exhibits emission wavelengths of 1274 nm with a fullwidth at half-maximum (FWHM) equal to 32 nm at room temperature. The laser structure demonstrates a peak at 1.27 μm with an FWHM equal to 2.6 nm under a continuous-wave operation with a threshold current density of ∼158 A/cm2 for a 4-μm narrow-ridge width InAs QD device. This work, therefore, paves the path for a monolithic solution for photonic integrated circuits when III−V light sources (which is required for Si photonics) are grown on a Ge-platform (engineered Ge-buffer on Si) for the integration of the CMOS part with other photonic devices on the same chip in near future.

Exploring the formation of InAs(Bi)/GaAs QDs at two growth-temperature regimes under different Bi supply conditions

The effect of a Bi supply on the development of InAs/GaAs (001) QDs has been structurally explored in two growth temperature regimes, one for Bi alloying (380 °C) and another for conventional formation of InAs QDs (510 °C). At high growth temperature (HT), there is no trace of Bi incorporation into the film and Bi acts as a surfactant limiting the diffusion length of In. All HT QDs are coherent and free of defects with an inverted cone-shaped In distribution. Increasing the Bi supply increases both the QD size and the In content (up to 40 %), while decreasing their areal density. At low temperature (LT), the addition of Bi goes beyond the surfactant role, promoting the transformation of the growth mode from 2D to 3D, resulting in an exponential increase in the QD size with Bi supply. Based on size, these LT QDs are divided into two populations in which the larger QDs relax plastically through the formation of misfit dislocations. LT QDs grown under a Bi flux reach a higher In content (80 %) with a homogeneous distribution within them. Remarkably, incorporation of Bi into larger QDs has been detected but it is not homogeneously distributed.

Telecom-wavelength InAs QDs with low fine structure splitting grown by droplet epitaxy on GaAs(111)A vicinal substrates

We present self-assembly of InAs/InAlAs quantum dots by the droplet epitaxy technique on vicinal GaAs(111)A substrates. The small miscut angle, while maintaining the symmetries imposed on the quantum dot from the surface, allows a fast growth rate thanks to the presence of preferential nucleation sites at the step edges. A 100 nm InAlAs metamorphic layer with In content ≥50% directly deposited on the GaAs substrate is already almost fully relaxed with a very flat surface. The quantum dots emit at the 1.3 μm telecom O-band with fine structure splitting as low as 16 μeV, thus making them suitable as photon sources in quantum communication networks using entangled photons.

Effects of dissipative electron tunneling manifested in the photocurrent of a GaAs p-i-n photodiode with a double InAs quantum dot layer

We report on the results of experimental studies of the photocurrent (PC) of photodiodes based on GaAs p-i-n structures with InAs/GaAs(001) double asymmetric quantum dot (DAQD) arrays obtained by self-assembling in the process of low-pressure metal-organic vapor phase epitaxy (LP-MOVPE). Three peaks were observed in the dependence of the PC on the reverse bias, measured under photoexcitation with a photon energy equal to the energy of the interband ground state transition in larger InAs QDs. These peaks were attributed to photoexcitation of electrons from the ground hole states in larger QDs into the ground electron states followed by resonant dissipative (with absorption or emission of optical phonons) and conservative tunneling into the GaAs conduction band via the ground electron states in smaller QDs. The PC dependence on the bias voltage agrees qualitatively with the theoretical field dependence of the probability of 1D dissipative tunneling between the QDs.

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.

Self‐Assembled InAs/GaAs Coupled Quantum Dots for Photonic Quantum Technologies

AbstractCoupled quantum dots (CQDs) that consist of two InAs QDs stacked along the growth direction and separated by a relatively thin tunnel barrier have been the focus of extensive research efforts. The expansion of available states enabled by the formation of delocalized molecular wavefunctions in these systems has led to significant enhancement of the already substantial capabilities of single QD systems and have proven to be a fertile platform for studying light–matter interactions, from semi‐classical to purely quantum phenomena. Observations unique to CQDs, including tunable g‐factors and radiative lifetimes, in situ control of exchange interactions, coherent phonon effects, manipulation of multiple spins, and nondestructive spin readout, along with possibilities such as quantum‐to‐quantum transduction with error correction and multipartite entanglement, open new and exciting opportunities for CQD‐based photonic quantum technologies. This review is focused on recent CQD work, highlighting aspects where CQDs provide a unique advantage and with an emphasis on results relevant to photonic quantum technologies.

Raman study of InAs/GaAs quantum dot solar cells

We report polarized and resonant Raman study of InAs/GaAs quantum dot solar cell (QDSC) structures. Raman spectra obtained from the top surfaces of the samples suggested that the formation of InAs QDs induced tensile strain in the overgrown GaAs layers. Furthermore, a longitudinal optical phonon-plasmon (LPP) coupled modes were observed in the p-type GaAs layers. The tensile strain was increased with an increase in the QD size. The hole concentrations estimated by fitting the individual LPP coupled modes were in the range of 2.4–3.5 × 1018 cm−3. Resonant Raman spectra obtained from the cleaved sides, where the QDs were located, showed a 225 cm−1 mode in parallel polarization configurations. Based on accurate analysis, this mode was identified as the LA(X) phonon of GaAs.

Ultrafast electronic spectroscopy on the coupling of Stranski-Krastanov and submonolayer quantum dots for potential application in near infrared light harvesting

Heterogeneously coupled self-assembled InAs QDs are always attractive to study their unique physical properties. Here, we have introduced Stranski-Krastanov (SK) grown InAs/GaAs QDs coupled to InAs/InGaAs submonolayer (SML) QDs to improve the light harvesting efficacy in the near infrared region (NIR) of the solar spectrum. Carrier migration mechanism from the SML stacks to the SK QDs and its dependence on the barrier thickness have been studied by temperature dependent steady state and picosecond resolved photoluminescence measurements. Both high and low energy excitations have been used to study the carrier migration and capture dynamics in the coupled heterostructures. It has been observed that the coupling is essentially determined by the spatial separation of both the QDs and the carrier lifetime reaches a maximum value at a certain barrier thickness. After successful optimization of the barrier thickness, we have used the SK-SML coupled structure as an active layer in a device to study its light harvesting efficacy. The SK-SML coupled device shows higher photocurrent, less saturation current and higher photovoltage compared to the uncoupled SK-QD one. In this study, we also find that the coupling in between the two classes of QDs increases the charge extraction efficiency and reduces the nonradiative recombination in the heterostructures. In brief, our experiments provide key information of the coupling mechanisms in the SK-SML coupled structure across various barrier thicknesses and its implication for improved device performance.

Tuning the optical properties of InAs QDs by means of digitally-alloyed GaAsSb strain reducing layers

In this work, we demonstrate the use of a digitally alloyed GaAsSb as a strain reducing layer (SRL) to tune the optical properties of InAs quantum dots grown on GaAs substrates. The GaAsSb digital alloy was made using a short period GaAs/GaSb superlattice. Increasing the Sb-shutter duty cycle (Sb-SDC) from 0 to 0.35 redshifts the emission wavelength from 1220 nm to 1492 nm at 300 K. The wavelength red shift is attributed mainly to the increased Sb content in the GaAsSb SRL as confirmed by high resolution X-ray diffraction. Power dependent photoluminescence showed a type II band alignment for the samples grown with a Sb-SDC of 0.25 and 0.35. Reversing the growth order of GaAs and GaSb layers and maintaining the same Sb-SDC (0.25) drastically alters the optical properties of the QDs. A large wavelength blue shift of 143 nm and a transformation from a type II to type I emission were observed as a result of GaSb intermixing with InAs QDs.

Achieving wavelength emission beyond the C-band from Type-II InAs-GaAsSb quantum dots grown monolithically on silicon substrate

Abstract The optical quality enhancement of a GaAs template grown on Silicon substrate using InGaAs/GaAs Dislocation Filters (DFs) combined with an annealing step have been assessed optically using Photoluminescence (PL) of embedded InAs/InGaAs QDs within a GaAs matrix. An annealing temperature after the growth of the DFs of 690 °C was shown to be optimum, giving an enhanced PL emission from the embedded InAs QDs in terms of intensity and Full Width at Half Maximum (FWHM). InAs quantum dots capped with GaAsSb grown at different temperatures were grown on the optimized GaAs template on Si. The prepared samples were characterized by PL, Atomic Force Microscopy (AFM), excitation power and dependent PL at 77 K and 300 K. At 77 K, the InAs/GaAsSb grown at 484 °C showed a type II band alignment with an emission wavelength of 1297 nm, which is shorter than the emission obtained from the reference sample, where the GaAsSb-capped dots were grown on GaAs (1357 nm). By reducing the GaAsSb capping layer growth temperatures to 465 °C and 450 °C, the wavelength at 77 K was extended to 1375 nm and 1480 nm respectively, resulting from an increased Sb content in the capping layer. At 300 K, a long wavelength emission of 1623 nm have been achieved.

Stacking of InAs QDs with Different Spacer Layer Thickness on GaAs Substrate by Molecular Beam Epitaxy

InAs QDs were grown by supplying 2.5 mono-layers (MLs) of InAs at 500 °C in a molecular beam epitaxial (MBE) system. The QDs are approximately 4–6 nm height with an areal density of 3×85 ×1010 cm−2 for single layer QDs. Typical diameter was found to be about 15–25 nm. InAs QDs were stacked with the spacer layer thickness of 5, 10, 15, 25 and 35 nm. For 15 nm of spacer layer thickness the QDs density decreased to 2.62×1010 cm−2 and again increased for 35 nm spacer layer and reached to the value of 3.65×1010 cm−2. The 14 K photoluminescence (PL) spectra of single layer InAs QDs covered by GaAs layer centered at 1079 nm. For the stacking of InAs QDs with spacer layer thickness of 5 and 10 nm another peak appeared around 1100 nm due to size broadening of QDs because of strain propagation to next layer due to less thickness of spacer layer. When the thickness of the spacer layer increased to 35 nm the peak position is around 1073 nm and the intensity increased more than 3 fold when compare to single layer QDs.

Fabrication and characterization of multi-layer InAs/InGaAs quantum dot p-i-n GaAs solar cells grown on silicon substrates

This paper reports on InAs/InGaAs quantum dot solar cells (QDSCs) deposited by molecular beam epitaxy (MBE) on (001) n-type silicon (n-Si) substrates. In-situ RHEED measurements show that InAs/InGaAs QDs SC has a high crystalline structure. The dislocation density in the active layer of the InAs/InGaAs QDSC and the lattice mismatch in the GaAs layer can be reduced by using an Si rough surface buffer layer (RSi). To show the effect of the QD layers, a reference SC with the same p-i-n structure as the InAs/InGaAs QDSC, but without InAs QDs, is also grown. The two SCs were studied by sepectroscopic ellipsometry (SE), in the 1–6 eV photon energy range, photoluminescence and photocurrent measurements. The optical constants of the two devices are determined in the photon energy range 1–6 eV from the SE data. The dominant features in the dielectric function spectra at ~ 3 and ~ 4.5 eV are attributed, respectively, to the E1 and E2 critical point structures of GaAs and InAs. The low-temperature photoluminescence spectrum of the InAs/InGaAs QDSC shows ground-state emissions, respectively, from the relatively small QDs near 1081 nm and from the large QDs near 1126 nm. Photocurrent measurements confirm the improved absorption performance (up to 1200 nm) of the InAs QDs SC which is ascribed to the optical absorption from the InAs/InGaAs QDs and the Si substrate as demonstrated by SE and photoluminescence measurements.

Emission properties of individual InAs/Al0.44Ga0.56As quantum dots

We report on micro-photoluminescence studies of InAs/AlGaAs single self-assembled quantum dots grown by molecular beam epitaxy. A variation of the exciton fine structure splitting induced by the anisotropic part of the electron-hole exchange interaction is systematically studied depending on the exciton emission energy and the insertion of a GaAs interlayer prior formation of the InAs QDs.

Emission and HR-XRD study of InGaAs/GaAs quantum wells with InAs quantum dots grown at different temperatures

GaAs/In0.15Ga0.85As/GaAs QWs with embedded InAs QDs grown at different temperatures have been studied by means of the photoluminescence (PL), X ray diffraction (XRD) and high resolution XRD (HR-XRD) methods. PL study has detected varying of QD parameters and HR-XRD permits monitoring the QW parameters. It is shown that increasing the QD growth temperature up to 510 °C leads to raising the QD sizes, to shift of QD emission peak to low energy and increasing the PL intensity of QDs. Simultaneously Ga/In atom intermixing is realized mainly between the InGaAs buffer and InAs wetting layers and did not influent on the InAs QD composition. At higher QD growth temperatures (525–535 °C) the PL intensity of QDs decreases significantly together with decreasing the QD heights and the shift of PL peaks into higher energy. Fitting the HR-XRD results has revealed that Ga/In atom intermixing involves the composition changes in buffer and wetting layers, as well as in QDs. The mentioned optical and structural effects have been discussed in details.