Carrier Quantum Research Articles

Interfacial micro-structure and properties of TiO2/SnO2 heterostructures with rutile phase: A DFT calculation investigation

Composite photocatalyst with heterostructure is often recognized as an effective strategy to achieve efficient charge separation and increase carrier concentration. In this study, the (1 1 0) and (1 0 1) surfaces of TiO2 and SnO2 were chosen to construct the abrupt and graded TiO2/SnO2 hetero-structures. The interface properties and band offsets of four heterostructures are calculated and analyzed in detail. It was found that the graded heterostructures are more stable and easier to preparation than the abrupt heterostructures, the charge depletion and accumulation occur at both ends of the transition layer. The interfacial electric field caused by this effect allows the photo-generated electron-hole pairs to be easily separated and transferred in the opposite direction at the interface, which is important for improving the photocatalytic activity. In addition, the intrinsic mechanism of the four hetero-structures is discussed according to the analysis of the band offset, which belongs to the type II heterostructures. For TiO2/SnO2-(1 1 0) heterostructure, the photo-generated electrons transfer from the conduction band of TiO2 to the conduction band of SnO2, while the photo-generated holes transfer from the SnO2 to the valence band of TiO2. This phenomenon leads to the accumulation of the photo-generated electrons in the conduction band of TiO2, accumulation of the photo-generated holes in the valence band of SnO2. In short, the graded heterostructure has more favorable effects to enhance the photocatalytic activity than that of the abrupt heterostructure. The internal electric field at the TiO2/SnO2 interface acts as a selector for photo-generated carriers, which may lead to higher photocatalytic quantum efficiency and carrier concentration under the same external conditions. These intrinsic photocatalytic mechanisms and the interpretation of the interfacial microscopic properties of heterostructure can be used as a basis for the design of the sensing devices and composite photocatalysts with heterostructures.

Performance enhancement of AlGaN-based UV-LEDs inserted with a pin-doped AlGaN layer between the active region and electron-blocking layer

The AlGaN-based deep ultraviolet light-emitting diodes with an Mg-Si pin-doped AlGaN layer inserted, between the active region and electron-blocking layer, have been systematically investigated by APSYS software. The energy band diagram, carrier distribution, and radiative recombination are studied. When compared with the conventional deep ultraviolet light-emitting diodes, the simulation results demonstrate that the proposed structure has effectively improved the output power, internal quantum efficiency, carrier concentrations, and radiative recombination rate. Based on the analysis of electrical and optical properties, and the performance improvements provided by using a pin-doped layer, we conclude that they are mainly attributed to the suppression of quantum-confined Stark effect as well as electron confinement and hole-injection enhancement in the active region effectively. In addition, the optimized thickness of this insert layer has been achieved after detailed research. As a result, the AlGaN-based deep ultraviolet light-emitting diodes with 10-nm-thick insert layer demonstrate improved performance.

(Invited) RF Pump-Probe Modulation Spectroscopy of Silicon Nanocrystals: Determination of the Carrier Dynamics and Quantum Efficiency

We present our latest work on the development of an all-optical (pump-probe) technique for estimating the quantum efficiency (QE) of silicon nanocrystals. Our experiment combines measurement of micro-photoluminescence and reflectivity when driven with an RF frequency modulated pump. By varying this frequency over a wide (5 decade) range, we are able to determine the dynamics of the free carrier concentration (multi-component in these systems) and thus retrieve the PL decay rate(s). Interestingly, we find that, in addition to the dominant (10’s-us) component (typically noted from direct measurement of the PL decay), a very slow component persists (in the ms regime), which we attribute to the recombination of ‘trapped’ charges. The technique provides a method for estimating the relative QE as a function of carrier concentration, providing clues as to the efficiency limiting processes in these materials. We present our most recent data for silicon nanocrystals formed in glass cover-slips after ion implantation and thermal annealing, and we discuss how the technique can be applied to luminescent materials more generally, e.g. to study the efficiency ‘droop’ mechanism observed at high carrier concentration in nitride based LED materials.

Spectrally-resolved internal quantum efficiency and carrier dynamics of semipolar core-shell triangular nanostripe GaN/InGaN LEDs

We investigate the spectrally resolved internal quantum efficiency (IQE) and carrier dynamics in semipolar core–shell triangular nanostripe light-emitting diodes (TLEDs) using temperature-dependent photoluminescence (TDPL) and time-resolved photoluminescence (TRPL) at various excitation energy densities. Using electroluminescence, photoluminescence, and cathodoluminescence measurements, we verify the origins of the broad emission spectra from the nanostructures and confirm that localized regions of high-indium-content InGaN exist along the apex of the nanostructures. Spectrally resolved IQE measurements are then performed, with the spectra integrated from 400–450 nm and 450–500 nm to obtain the IQE of the QWs mainly near the sidewalls and apex of the TLEDs, respectively. TDPL and TRPL are used to decouple the radiative and non-radiative carrier lifetimes for different regions of the emission spectra. We observe that the IQE is higher for the spectral region between 450 nm and 500 nm compared to the IQE between 400 and 450 nm. This result is in contrast to the typical observation that the IQE of planar GaN-based LEDs is lower for longer wavelengths (i.e., higher indium contents). We also observe a longer non-radiative recombination lifetime for the longer wavelength portion of the spectrum. Several explanations are proposed for the improved IQE and longer non-radiative lifetime observed near the apex of the nanostructures. The results show that nanostructures may be leveraged to design more efficient green LEDs, potentially addressing a long-standing challenge in GaN-based materials.

Thickness Control of the Spin-Polarized Two-Dimensional Electron Gas in LaAlO3/BaTiO3 Superlattices

We explored the possibility of increasing the interfacial carrier quantum confinement, mobility and conductivity in the (LaAlO3)n/(BaTiO3)n superlattices by thickness regulation using the first-principles electronic structure calculations. Through constructing two different interfacial types of LaAlO3/BaTiO3 superlattices, we discovered that the LaO/TiO2 interface is preferred from cleavage energy consideration. We then studied the electronic characteristics of two-dimensional electron gas (2DEG) produced at the LaO/TiO2 interface in the LaAlO3/BaTiO3 superlattices via spin-polarized density functional theory calculations. The charge carrier density of 2DEG has a magnitude of 1014 cm−2 (larger than the traditional system LaAlO3/SrTiO3), which is mainly provided by the interfacial Ti 3dxy orbitals when the thicknesses of LaAlO3 and BaTiO3 layers are over 4.5 unit cells. We have also revealed the interfacial electronic characteristics of the LaAlO3/BaTiO3 system, by showing the completely spin-polarized 2DEG mostly confined at the superlattice interface. The interfacial charge carrier mobility and conductivity are found to be converged beyond the critical thickness. Therefore, we can regulate the interfacial confinement for the spin-polarized 2DEG and quantum transport properties in LaAlO3/BaTiO3 superlattice via controlling the thicknesses of the LaAlO3 and BaTiO3 layers.

Efficient Quantum Information Hiding for Remote Medical Image Sharing

Information hiding aims to embed secret data into the multimedia, such as image, audio, video, and text. In this paper, two new quantum information hiding approaches are put forward. A quantum steganography approach is proposed to hide a quantum secret image into a quantum cover image. The quantum secret image is encrypted first using a controlled-NOT gate to demonstrate the security of the embedded data. The encrypted secret image is embedded into the quantum cover image using the two most and least significant qubits. In addition, a quantum image watermarking approach is presented to hide a quantum watermark gray image into a quantum carrier image. The quantum watermark image, which is scrambled by utilizing Arnold’s cat map, is then embedded into the quantum carrier image using the two least and most significant qubits. Only the watermarked image and the key are sufficient to extract the embedded quantum watermark image. The proposed novelty has been illustrated using a scenario of sharing medical imagery between two remote hospitals. The simulation and analysis demonstrate that the two newly proposed approaches have excellent visual quality and high embedding capacity and security.

Electronic transport anisotropy of 2D carriers in biaxial compressive strained germanium

The anisotropic nature of carrier mobility in simple cubic crystalline semiconductors, such as technologically important silicon and germanium, is well understood as a consequence of effective mass anisotropy arising from a change in band structure along non-identical surface crystal directions. In contrast to this, we show experimentally that this type of anisotropy is not the dominant contribution. Recent advances in epitaxial growth of high quality germanium enabled the appearance of high mobility 2D carriers suitable for such an experiment. A strong anisotropy of 2D carrier mobility, effective mass, quantum, and transport lifetime has been observed, through measurements of quantum phenomena at low temperatures, between the ⟨110⟩ and ⟨100⟩ in-plane crystallographic directions. These results have important consequences for electronic devices and sensor designs and suggest similar effects could be observed in technologically relevant and emerging materials such as SiGe, SiC, GeSn, GeSnSi, and C (Diamond).

A Novel Quantum Video Steganography Protocol with Large Payload Based on MCQI Quantum Video

As one of important multimedia forms in quantum network, quantum video attracts more and more attention of experts and scholars in the world. A secure quantum video steganography protocol with large payload based on the video strip encoding method called as MCQI (Multi-Channel Quantum Images) is proposed in this paper. The new protocol randomly embeds the secret information with the form of quantum video into quantum carrier video on the basis of unique features of video frames. It exploits to embed quantum video as secret information for covert communication. As a result, its capacity are greatly expanded compared with the previous quantum steganography achievements. Meanwhile, the new protocol also achieves good security and imperceptibility by virtue of the randomization of embedding positions and efficient use of redundant frames. Furthermore, the receiver enables to extract secret information from stego video without retaining the original carrier video, and restore the original quantum video as a follow. The simulation and experiment results prove that the algorithm not only has good imperceptibility, high security, but also has large payload.

Analytical prediction of carbon nanoscroll-based electrochemical glucose biosensor performance

ABSTRACTCarbon nanoscroll (CNS) with extraordinary electrical, physical and optical properties is an ideal candidate on sensor applications. It has great potential in biosensing owing to its outstanding properties like large surface-to-volume ratio, high conductivity, high flexibility and biocompatibility. In this research, we demonstrate a CNS-based biosensor to electrochemically detect glucose with high specificity and sensitivity. To this end, glucose absorption effect on the sensing area in the form of carrier concentration and quantum capacitance variations is investigated. Also, the caused electrical response on CNS as a detection element is analytically proposed, in which significant current increase of the CNS-based biosensor is observed after exposure to glucose. The proposed CNS-based glucose biosensor exposes higher current compared to that of carbon nanotube counterpart for analogous ambient conditions. Moreover, the comparative results provide evidence of good consensus between the model and experimental data of platinum nanoparticles/graphene nanoscrolls (Pt/GSS) and Pt/nitrogen-doped GSS (Pt/N-GSS) nanocomposites-based biosensors. Main findings of this research can be served as a high throughput platform to analytically predict the behaviour of the sensing mechanism in glucose biosensors. The results further reveal that the CNS biosensor demonstrates not only high sensitivity and broad linear range but also long-term stability and low detection limit.

Influence of Different Metals Back Surface Field on BSF Silicon Solar Cell Performance Deposited by Thermal Evaporation Method

This paper presents comparison of thermal evaporation method based passivation and BSF formation with different materials (Au, Al, and Cu). Silicon solar cells with different rear surface contact using these materials were fabricated. A comprehensive comparison of the samples have been carried out to find better back surface contact regarding the efficiency by investigating I-V characteristics, fill factor, external quantum efficiency and carrier diffusion length and lifetime, etc. Experimental data revealed that Cu based back surface contact has maximum output efficiency of about 13.73%, whereas Au shows maximum external quantum efficiency of about 86%. Moreover, use of Al shows the maximum carrier diffusion length 97.2μm and highest carrier lifetime of 3.5μs with overall cell efficiency of 12.90% indicating that Al is a promising material for back contact for n+-p-p+ back surface field silicon solar cell.

Comprehensive Capacitance–Voltage Simulation and Extraction Tool Including Quantum Effects for High-k on Si<italic>x</italic>Ge1−<italic>x</italic> and In<italic>x</italic>Ga1−<italic>x</italic>As: Part I—Model Description and Validation

High-mobility alternative channel materials to silicon are critical to the continued scaling of MOS devices. The analysis of capacitance–voltage (C–V) measurements on these new materials with high-k gate dielectrics is a critical technique to determine many important gate-stack parameters. While there are very useful C–V analysis tools available to the community, these tools are all limited in their applicability to alternative semiconductor channel MOS gate-stack analysis since they were developed for silicon. Here, we report on a new comprehensive C–V simulation and extraction tool, called CV Alternative Channel Extraction (ACE), that incorporates a wide range of semiconductors and dielectrics with the capability to implement customized gate stacks. Fermi–Dirac carrier statistics, nonparabolic bands, and quantum mechanical effects are all implemented with options to turn each of these off as the user desires. Interface state capacitance ( ${C}_{\mathsf {it}}$ ) is implemented using a common model for systems like Si and Ge. A more complex ${C}_{\mathsf {it}}$ model is also implemented for III–Vs that accurately captures frequency dispersion in accumulation that arises from tunneling. CV ACE enables extremely fast simulation and extraction and can accommodate measurements performed at variable temperatures and frequencies to allow for a more accurate extraction of interface state density ( ${D}_{\mathsf {it}}$ ).

A Robust Quantum Watermark Algorithm Based on Quantum Log-polar Images

Copyright protection for quantum image is an important research branch of quantum information technology. In this paper, based on quantum log-polar image (QUALPI), a new quantum watermark algorithm is proposed to better protect copyright of quantum image. In order to realize quantum watermark embedding, the least significant qubit (LSQb) of quantum carrier image is replaced by quantum watermark image. The new algorithm has good practicability for designing quantum circuits of embedding and extracting watermark image respectively. Compared to previous quantum watermark algorithms, the new algorithm effectively utilizes two important properties of log-polar sampling, i.e., rotation and scale invariances. These invariances make quantum watermark image extracted have a good robustness when stego image was subjected to various geometric attacks, such as rotation, flip, scaling and translation. Experimental simulation based on MATLAB shows that the new algorithm has a good performance on robustness, transparency and capacity.

The quantum carrier pigeon that wasn’t there

It’s difficult to grasp the implications of an experiment that seemingly sent data from Bob to Alice without any physical messenger passing between them.

Giant optical gain in a single-crystal erbium chloride silicate nanowire

Rare-earth optical materials with large optical gain are of great importance for a wide variety of applications in photonics and quantum information due to their long carrier lifetimes and quantum coherence times, especially in the realization of efficient lasers and amplifiers. Until now, such materials have achieved a gain of less than a few dB cm–1, rendering them unsuitable for applications in nanophotonic integrated circuits. Here, we report the results of the signal enhancement and transmission experiments on a single-crystal erbium chloride silicate nanowire. Our experiments demonstrate that a net material gain over 100 dB cm–1 at wavelengths around 1,530 nm is possible due to the nanowire's single-crystalline material quality and its high erbium concentration. Our results establish that such rare-earth-compound nanowires are a potentially important class of nanomaterials for a variety of applications including, for example, subwavelength-scale optical amplifiers and lasers for integrated nanophotonics, and quantum information. Erbium chloride silicate nanowire promises optical gain for nanophotonic circuits.

Efficient PL Emission from p-type Porous Silicon: A Comparative Study for Selection of Effective Anodization Parameters

The physical mechanism of highly efficient photoluminescence (PL) emission from p-type silicon is described by a comparative study of the effectiveness of the etching parameters in an electrochemical anodization technique. Two series of porous silicon samples were prepared in a combination of anodization current and time, to maintain the total amount of anodic charge transfer constant. Photoluminescence studies show that irrespective of the amount of charge transfer, the samples prepared with comparatively higher current density show an efficient PL as well as stronger blueshift in the emission energy vis-a-vis the samples prepared for longer durations. An overall decrease in crystallite size, as estimated by Raman spectral analysis, was observed for both series of samples with the progress of charge transfer. Comparative analysis shows a marginal difference in crystallite size for both series of samples in the initial state of charge transfer, whereas major differences arise at higher values. This is explained with the formation of silicon suboxide on the porous surface at higher current density, leading to initiation of side wall reaction, and higher reduction rate in crystallite size as well as strong luminescence due to the carrier quantum confinement effect.

Improvement of minority carrier collection and quantum efficiency in graphene planar silicon solar cell

Graphene planar silicon heterojunction solar cells were investigated using 2D physics-based TCAD simulation. A planar structure consisting of graphene layer as the hole transport material, and n-type silicon as substrate is simulated. Process modeling has been carried out especially for highly boron diffusion. Using this model, the effect of the highly doped surface inverse region located as 0.08, 0.22, 0.35 μm on the photovoltaic performance has been studied. The obtained J–V characteristic is analyzed to study effects of the inverse region depth and doping concentration on Schottky junction modification. The proposed design proves to be highly efficient in 0.2 h annealing, which provides a new platform to further enhance the performance of graphene planar solar cell.

Photoconduction properties and anomalous power-dependent quantum efficiency in non-polar ZnO epitaxial films grown by chemical vapor deposition

Photoconduction (PC) properties in the ZnO films with the (110) nonpolar surface (a-plane) epitaxially grown by chemical vapor deposition on the LiGaO2 (010) substrates with low lattice mismatches (4.0% along the c-axis and 3.8% along the m-axis) have been studied. The structural and optical qualities of the epitaxial films have been characterized using theta-two theta and phi scans, X-ray diffraction, rocking curve, and photoluminescence measurements. The nonpolar ZnO film exhibits a near visible-blind ultraviolet photoresponse. The optimal photocurrent to dark current ratio (i.e., sensitivity) can reach 13360%. The responsivity of the a-plane ZnO photoconductor-type detector can also reach 17 AW−1, which is two to four orders of magnitude higher than those of the m-plane, a-plane, and r-plane photodiodes based on ZnO/ZnMgO quantum wells. The normalized gain at 2.9 cm2V−1 of the nonpolar film is also comparable with the optimal recorded value of the ZnO nanowires. In addition, the PC mechanism has also been investigated by the power-dependent and time-resolved photoconductivity measurements. The power-sensitive responsivity can be attributed to the effect of light intensity on carrier lifetime and quantum efficiency. The photovoltaic effect of the surface depletion region is inferred to be the reason resulting in the anomalous power-dependent quantum efficiency.

Internal quantum efficiency and carrier dynamics in semipolar (2021) InGaN/GaN light-emitting diodes.

The internal quantum efficiencies (IQE) and carrier lifetimes of semipolar (202¯1¯) InGaN/GaN LEDs with different active regions are measured using temperature-dependent, carrier-density-dependent, and time-resolved photoluminescence. Three active regions are investigated: one 12-nm-thick single quantum well (SQW), two 6-nm-thick QWs, and three 4-nm-thick QWs. The IQE is highest for the 12-nm-thick SQW and decreases as the well width decreases. The radiative lifetimes are similar for all structures, while the nonradiative lifetimes decrease as the well width decreases. The superior IQE and longer nonradiative lifetime of the SQW structure suggests using thick SQW active regions for high brightness semipolar (202¯1¯) LEDs.

Methods for modeling non-equilibrium degenerate statistics and quantum-confined scattering in 3D ensemble Monte Carlo transport simulations

Particle-based ensemble semi-classical Monte Carlo (MC) methods employ quantum corrections (QCs) to address quantum confinement and degenerate carrier populations to model tomorrow's ultra-scaled metal-oxide-semiconductor-field-effect-transistors. Here, we present the most complete treatment of quantum confinement and carrier degeneracy effects in a three-dimensional (3D) MC device simulator to date, and illustrate their significance through simulation of n-channel Si and III-V FinFETs. Original contributions include our treatment of far-from-equilibrium degenerate statistics and QC-based modeling of surface-roughness scattering, as well as considering quantum-confined phonon and ionized-impurity scattering in 3D. Typical MC simulations approximate degenerate carrier populations as Fermi distributions to model the Pauli-blocking (PB) of scattering to occupied final states. To allow for increasingly far-from-equilibrium non-Fermi carrier distributions in ultra-scaled and III-V devices, we instead generate the final-state occupation probabilities used for PB by sampling the local carrier populations as function of energy and energy valley. This process is aided by the use of fractional carriers or sub-carriers, which minimizes classical carrier-carrier scattering intrinsically incompatible with degenerate statistics. Quantum-confinement effects are addressed through quantum-correction potentials (QCPs) generated from coupled Schrödinger-Poisson solvers, as commonly done. However, we use these valley- and orientation-dependent QCPs not just to redistribute carriers in real space, or even among energy valleys, but also to calculate confinement-dependent phonon, ionized-impurity, and surface-roughness scattering rates. FinFET simulations are used to illustrate the contributions of each of these QCs. Collectively, these quantum effects can substantially reduce and even eliminate otherwise expected benefits of considered In0.53Ga0.47As FinFETs over otherwise identical Si FinFETs despite higher thermal velocities in In0.53Ga0.47As. It also may be possible to extend these basic uses of QCPs, however calculated, to still more computationally efficient drift-diffusion and hydrodynamic simulations, and the basic concepts even to compact device modeling.

Photogeneration and Mobility of Charge Carriers in Atomically Thin Colloidal InSe Nanosheets Probed by Ultrafast Terahertz Spectroscopy.

The implementation of next generation ultrathin electronics by applying highly promising dimensionality-dependent physical properties of two-dimensional (2D) semiconductors is ever increasing. In this context, the van der Waals layered semiconductor InSe has proven its potential as photodetecting material with high charge carrier mobility. We have determined the photogeneration charge carrier quantum yield and mobility in atomically thin colloidal InSe nanosheets (inorganic layer thickness 0.8-1.7 nm, mono/double-layers, ≤ 5 nm including ligands) by ultrafast transient terahertz (THz) spectroscopy. A near unity quantum yield of free charge carriers is determined for low photoexcitation density. The charge carrier quantum yield decreases at higher excitation density due to recombination of electrons and holes, leading to the formation of neutral excitons. In the THz frequency domain, we probe a charge mobility as high as 20 ± 2 cm2/(V s). The THz mobility is similar to field-effect transistor mobilities extracted from unmodified exfoliated thin InSe devices. The current work provides the first results on charge carrier dynamics in ultrathin colloidal InSe nanosheets.