Subband Energy Levels Research Articles

Effects of external fields and structural parameters on third harmonic generation of GaAs/AlGaAs Manning-like double quantum well structure

In this theoretical work, we investigate how external fields like as electric, magnetic, and intense laser fields, as well as structural factors, affect the third harmonic generation (THG) coefficient of an AlGaAs/GaAs Manning-like double quantum well heterostructure. To achieve our goals, we numerically solve the time-independent Schrödinger equation using the diagonalization approach with the effective mass approximation and then derive the subband energy levels and corresponding wave functions of the structure. After that, we derive the mathematical expression of the THG coefficient by using the compact density matrix method. According to our results, the resonance peaks of the THG coefficient show shifting to the high-energy region with an increase in the field’s magnitude in cases where external fields (electric, magnetic, and intense laser) are applied separately. At the same time, increasing the depth (width) of the quantum well structure causes the THG peaks to shift to the high (low) energy region. We believe that the findings from this search will have a substantial impact on existing experimental device designs and applications.

Dynamics of the nonlinear optical second- and third-harmonic generation in quantum well due to hydrostatic pressure and temperature

We studied the effects of hydrostatic pressure and temperature on the second- and third-harmonic generation (SHG and THG) in semi-parabolic GaAs/Al0.3Ga0.7As quantum wells. By solving the Schrödinger equation numerically, we can determine the system's sub-band energy levels and wave functions, and then calculate its optical gain. The numerical simulation results show that both temperature and hydrostatic pressure can effectively improve the nonlinear optical performance of the system. Notably, we explore the mechanisms underlying these interactions. These findings suggest a viable approach to adjust the nonlinear optical performance of GaAs/Al0.3Ga0.7As quantum system through the subtle interaction between hydrostatic pressure, temperature and structural parameters.

Analytical Modeling for Photocurrent and Detectivity of TiO2/ZnS Core‐Shell Quantum Dot Photodetectors

AbstractIn this paper, a theoretical model has been presented to calculate the photocurrent and detectivity in a TiO2/ZnS core‐shell quantum dot (CSQD) photodetector. Analytical modeling permits to calculate the available photocurrent and corresponding detectivity from the CSQD structures. In this theoretical model, the subband energy levels of the CSQD are estimated using the 3D symmetric quantum box structures with a finite potential barrier. The finite band offset determines the number of available subband energy levels in the CSQD structures depending on the size of the core. Theoretical results show the variation of photocurrent and corresponding detectivity with different core sizes of the CSQD for a constant shell thickness. The calculations indicate that for electronic intersubband transitions detectivity is higher compared with the hole transitions.

Wannier–Stark localization of electronic states in 4H-SiC MOS inversion layer

The electronic states in 4H-SiC MOS inversion layers are theoretically analyzed using the empirical pseudopotential method (EPM). The analysis shows that the Wannier–Stark localization occurs, which is absent in an effective mass approximation (EMA). The Wannier–Stark localization modifies the electronic states in the MOS inversion layers. A model is proposed to describe the in-plane dispersion of subbands affected by the Wannier–Stark localization. The differences between the EPM and EMA results for the subband energy levels and the in-plane effective masses are discussed.

Effect of structure parameters on electron mobility in asymmetric V-shaped double quantum well structure

Here, we analyse the effect of structure parameters like well width (w), central barrier width (b), and alloy concentration (x) on multisubband electron mobility μ in a GaAs-AlxGa1-xAs based modulation doped asymmetric V-shaped-double-quantum-well (VDQW) structure. The asymmetry in the structure potential is generated through the difference in the doping concentrations (N d ) in the side barriers i.e., N d1 (0 to 4 × 1018 cm−3) and N d2 (2 × 1018 cm−3). The mobility μ is calculated by considering ionised impurity (imp) and alloy disorder (ad) scattering mechanisms. The continuous variation of x inside the well makes μ ad < μ imp resulting in the dominance of ad-scattering on μ as a function of N d1. As a result, at the interface an increase in x from 0.1 to 0.3 reduces μ around 40%. However, an increase in w symmetrically (w 1 = w 2) enhances μ. Further, the introduction of non-symmetric well profile (w 1 ≠ w 2) not only causes asymmetric redistribution of subband wave functions ψ 0 and ψ 1 in the wells, but also changes the position and hence occupation of subband energy levels, thereby influencing the subband mobility. As the difference in w 1 and w 2 increases, the system becomes more and more single subband occupied as a function of N d1 and hence the mobility enhances due to the absence of intersubband scattering. Our results also reflected that an increase in b from 20 Å to 80 Å has a marginal effect on μ during single subband occupancy but improves μ during double subband occupancy through intersubband interaction.

Flexible Antenna Sensor in Thumb Spica Splint for Noninvasive Monitoring of Fluctuating Blood Glucose Levels

Antenna is used as a sensor in wearable technology because of its small size. Reduced flexible antenna size avoids mounting problems and crumbling effects on the human skin region during signal acquisition. Moreover, continuous diabetes monitoring needs an efficient antenna sensor design. In this article, we develop a continuous glucose monitoring device using a flexible antenna sensor planted inside the thumb spica splint glove. The flexible antenna sensor comprises polyimide substrate with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\xi _{r}$ </tex-math></inline-formula> = 3.5, tan <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> = 0.0027, and a thickness of 0.1 mm. The proposed flexible antenna sensor senses dielectric radiations from glucose in the blood and improves the accuracy of glucose-level prediction. Traditional antenna sensor methods use skin layers and muscles as sources of permittivity, resulting in errors in diabetic value measurement. The acquired antenna sensor signal from the designed thumb spica splint glove is processed using the tunable <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> -factor wavelet transform (TQWT) algorithm. It differentiates the dielectric properties of glucose in the blood, skin, and muscle through subband energy levels. The subband energy level of glucose from the proposed antenna sensor and the quadratic regression algorithm is used to predict the human glucose level. The predicted glucose levels using the proposed flexible antenna are validated through Accu-Chek Active Glucometer. From experimental results, the proposed method-based glucose prediction-level accuracy achieved about 96.8% compared to traditional methods.

Effect of the AlN strain compensation layer on InGaN quantum well red-light-emitting diodes beyond epitaxy.

An atomically thick AlN layer is typically used as the strain compensation layer (SCL) for InGaN-based-red light-emitting diodes (LEDs). However, its impacts beyond strain control have not been reported, despite its drastically different electronic properties. In this Letter, we describe the fabrication and characterization of InGaN-based red LEDs with a wavelength of 628 nm. A 1-nm AlN layer was inserted between the InGaN quantum well (QW) and the GaN quantum barrier (QB) as the SCL. The output power of the fabricated red LED is greater than 1 mW at 100 mA current, and its peak on-wafer wall plug efficiency (WPE) is approximately 0.3%. Based on the fabricated device, we then used numerical simulation to systematically study the effect of the AlN SCL on the LED emission wavelength and operating voltage. The results show that the AlN SCL enhances the quantum confinement and modulates the polarization charges, modifying the device band bending and the subband energy level in the InGaN QW. Thus, the insertion of the SCL considerably affects the emission wavelength, and the effect on the emission wavelength varies with the SCL thickness and the Ga content introduced into the SCL. In addition, the AlN SCL in this work reduces the LED operating voltage by modulating the polarization electric field and energy band, facilitating carrier transport. This implies that heterojunction polarization and band engineering is an approach that can be extended to optimize the LED operating voltage. We believe our study better identifies the role of the AlN SCL in InGaN-based red LEDs, promoting their development and commercialization.

Effects of external fields on the nonlinear optical rectification and second harmonic generation of GaAs/GaAlAs zigzag quantum well

For the first time, the impact of externally applied static electric and magnetic field on the nonlinear optical rectification (NOR) and second harmonic generation (SHG) coefficients of GaAs/GaAlAs zigzag quantum well is theoretically investigated in this study. Additionally, we examined the effect of physical parameters such as width and depth of the structure on these coefficients. We have numerically solved the time-independent Schrödinger equation by using the diagonalization method under the effective mass approximation for obtaining subband energy levels and wave functions of the structure, and then we have used the compact density matrix method to obtain the analytical expressions of NOR and SHG coefficients. The obtained numerical results showed that when the magnitude of the externally applied electric and magnetic fields is increased, the peak position of NOR and SHG shifts to blue, and by increasing the width and potential depth of the quantum well, it shifts to red.

Sub-band response of PZT photodetector controlled by back-gate voltage

Sub-band energy levels induced photo-conduction mechanisms play a significant role in the extension of the response spectra within a photodetector. Herein, we reported a PbZr0.32Ti0.68O3 (PZT) based photodetector for sub-band photoresponse excited by a 450 nm blue laser. Sub-band induced by the defects acts as the intermediate state for the intra-band transition excited by the blue laser, in which the photon energy is smaller than the bandgap of the PZT thin film. Within both gate-controlled and blue laser driven operations, the source to drain current (I sd) can be precisely modulated. The photocurrent and response speeds of the device are also studied under air and vacuum conditions, which shows negligible fluctuations under different atmospheres and excludes the negative influence from the defect-related surface states. The proposed device configuration provides a simple and cost-effective visible light driven photodetector, which may give rise to an interesting route towards optoelectronic devices based on ferroelectric material.

Investigation of the electro-optical characteristics of GaAs/AlGaAs multiple quantum well grown by metal-organic vapor phase epitaxy

In this study, the photoluminescence measurements of GaAs/Al0.25Ga0.75As multi-quantum-wells heterojunction structure grown on n+-GaAs substrates by Metal Organic Vapor Phase Epitaxy (MOVPE) method are investigated. By dropping 5145 Å wavelength laser light on the sample at room temperature and low temperatures, the transitions between the bands in the structure and the changes in these transitions under the different electric fields and temperatures are observed. In addition, by making theoretically developed self-consistent potential calculations, the subband energy levels and their corresponding wave functions of the structure under the electric field and without the electric field are calculated. The obtained numerical results were found to be in full agreement with the experimental measurements and theoretical calculations.

The nonlinear optical properties of GaAs/GaAlAs triple quantum well: Role of the electromagnetic fields and structural parameters

Being relevant to the field of device applications, multiple semiconductor quantum wells are systems that exhibit remarkable optical and electronic properties. These can be properly tuned by suitably modifying the composition, structural parameters, and the application of external probes. Here, the electronic and optical properties of a GaAs/GaAlAs triple quantum well have been investigated under the influence of applied electric and magnetic fields, as well as the change of well and barrier widths. We have used the diagonalization method to numerically solve the Schrödinger equation under the effective mass approximation for obtaining the subband energy levels and related electronic wave functions. The expressions used for evaluating linear, third-order nonlinear, and total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs) were previously derived within the compact density matrix method. According to our results, whilst an increment in the applied electric field causes a red shift in TOACs and RRICs, a blue shift of the optical responses occurs with increasing the applied magnetic field. Besides, a blue shift is observed as well by changing the width of the central well (LwL), whilst a red shift is noticed when changing left and right wells (LwL and LwR) and barrier (LbL and LbR) widths for zero fields. We believe that our study could make a contribution to designing new quantum-well-based optoelectronic devices.

Nonlinear optical properties of GaAs/AlηGa1−ηAs quantum dots system with Hulthén-Yukawa potential

In this work, we primarily explore the effects of quantum dot radius, tunable effective mass and limiting potential depth on the second-harmonic generation and third-harmonic generation of GaAs/AlηGa1−ηAs quantum dots under Hulthén-Yukawa Potential. The subband energy levels and wave functions are obtained by solving Schrödinger equation by Nikiforov-Uvarov method is used to solve the equation corresponding to the restricted quantum dot system. Most important of all, the numerical simulation illustrates that these variables have a remarkable effect on the nonlinear optical coefficient of semiconductor systems.

Nonlinear optical rectification of GaAs/AlηGa1−ηAs quantum dots system with Hulthén-Yukawa Potential

The impacts of structural parameters on the nonlinear optical rectification (NOR) coefficient in GaAs/AlηGa1−ηAs quantum dots (QDs) with Hulthén-Yukawa Potential (HYP) are explored in the reported work, including quantum dot radius, limiting potential depth, Al-concentration, hydrostatic pressure and temperature. The Nikiforov-Uvarov (N–U) method is used to solve the Schrödinger equation corresponding to the restricted quantum dot system, at the same time, the subband energy level and the propagation wave function are obtained, the numerical expression of the NOR coefficient is calculated by using compact density matrix theory and iterative method. Last but not least, the results of data analysis show that these factors have an obvious influence on the nonlinear optical characteristics of the model system, it includes the change of peak value and the redshift or blueshift of coefficient formant.

Magnetoresistance sensor-based rotor fault detection in induction motor using non-decimated wavelet and streaming data

In this paper, the giant magnetoresistance broken rotor (GBR) method is used to diagnose the induction motor (IM) rotor bar fault at an early stage from outward magnetic flux developed by IM.The outward magnetic field signal has anti-clockwise radiation due to broken rotor bar current.In this paper, the outward magnetic signal is acquired using a giant magnetoresistance (GMR) sensor. In the GBR method, IM rotor fault is analysed with a non-decimated wavelet transform (NDWT)-based outward magnetic signal. Experimental result shows the difference in statistical features and energy levels of sub-bands of NDWT for healthy and faulty IM. Least square-support vector machine(LS-SVM)-based classification results are verified by confusion matrix based on 150 outward magnetic signals from a healthy and damaged rotor (broken rotor). The proposed method identifies IM rotor faults with 95% sensitivity, 90% specificity and 92.5% classification accuracy. Furthermore, run-time IM condition monitoring is performed through the ThinkSpeak internet of things (IoT) platform for collecting outer magnetic signal data. ThinkSpeak streaming data of outward magnetic field help detect rotor fault at the initial stage and understand the growth of rotor fault in the motor. The proposed GBR method overcomes sensitivity, translation-invariance limitations of existing IM rotor fault diagnosis methods.

Regulation of optical properties by applied external fields for a quantum well with Hulthen potential

In this present study, the effects of electric, magnetic, and non-resonant intense laser field (ILF) on the linear, third-order nonlinear, and total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs) of GaAs quantum well, having Hulthen confinement potential, were theoretically investigated. In addition, the dependence of the nonlinear optical properties in the structure on the optical intensity of incident photon and the inverse relaxation time was also calculated. To do this research, firstly the energy eigenvalues and eigenfunctions of the structure were calculated by using the effective mass and envelope function approaches. By using these calculated subband energy levels and wave functions belonging to these levels, the nonlinear optical properties of the system were obtained via the iterative method, within the compact density matrix approach framework. The obtained numerical results show that the optical properties of the considered system depend on the externally applied fields. With the applied external electric and magnetic field, the peak positions of TOACs and RRICs shift to higher energies, and the peak magnitudes increase. The high-frequency ILF applied to the structure shifts the peak positions of TOACs and RRICs initially towards higher energies and then towards lower energies and their peak sizes increase. These results show that the optical properties of the system can be adjusted purposively by changing the magnitude of applied external fields.

Analytical modelling for the dark current of TiO2/ZnS core shell quantum dot (CSQD) photodetectors

Dark current has a major contribution in the performance of a Quantum Dot (QD) photodetector. In this paper, a theoretical model is proposed to calculate the dark current of TiO2/ZnS CSQD photodetectors. In this model, the QD sub-band energy levels are calculated using three-dimensional symmetric quantum box considerations. The potential well is considered as finite. The observed theoretical results show the variation of electronic and hole sub-band transition variations with core size. It is also observed that, the dark current is very small, in order of 10−6 and lower for electronic transitions than the hole transitions for smaller, i.e. 8 nm core dimensions.

Nonlinear optical properties in AlxGa1-xAs/GaAs double-graded quantum wells: The effect of the structure parameter, static electric, and magnetic field

We present a theoretical simulation of the impact of applied external electric and magnetic fields, as well as of the change in structure parameters, on the nonlinear optical rectification (NOR), second harmonic generation (SHG), and third harmonic generation (THG) in typical GaAs/GaAlAs asymmetric double graded quantum wells (ADGQWs). At first, we have calculated the wave functions and the subband energy levels for the lowest bounded four states confined within the structure by solving the Schrödinger equation using the diagonalization method within the framework of the effective mass and single parabolic band approximations. Then, analytical expressions for the NOR, SHG, and THG that arise from the compact density matrix approach are used to evaluate the corresponding coefficients. The simulation results show that the applied external fields and the structure parameters play an important role in the optical properties of ADGQWs.

Optical properties of a quantum well with Razavy confinement potential: Role of applied external fields

In this present work, the effect of applied external fields and well width on the optical absorption and refractive index change coefficient of a GaAs quantum well with Razavy confinement potential is theoretically presented. For this, firstly, the confined subband energy levels of the structure and the envelope wave functions corresponding to these states have been computed using the diagonalization method within the framework of effective mass and parabolic band approximation. Then, by using this information, the coefficients of total – linear plus nonlinear – intersubband optical absorption (TOAC) and relative refractive index changes (RRIC) of the structure are evaluated. The obtained numerical results show that the increase in the magnitude of the applied external fields creates a blue shift in TOAC and RRIC. Also, contrarily to the applied external fields, an increment of the quantum well width have induced a red shift in the TOAC and RRIC. We discuss in detail the variation of the diagonal matrix elements and the energy difference (E2–E1) which are responsible for the change of amplitudes of the calculated coefficients. We believe that the obtained numerical results can be useful in the design and application of the next generation devices used in the optoelectronics field. • The magnitude of the TOACs peak decrease with the static electric field. • The magnitude of the TOACs peak increase with the ILF. • The magnitude of the RRICs decrease with the ILF. • The increase of ILF leads to important effects on the optical properties of Razavy QW.

Nonlinear optical properties in n-type quadruple δ-doped GaAs quantum wells

The effects of the interlayer distance on the nonlinear optical properties of n-type quadruple δ-doped GaAs quantum well were theoretically investigated. Particularly, the absorption coefficient and the relative refraction index change were determined. In the effective mass approach and within the framework of the Thomas–Fermi theory, the Schrödinger equation was resolved. Thereby, the subband energy levels and their respective wave functions were calculated. The variations in the nonlinear optical properties were determined by using the density matrix solutions. The achieved results demonstrate that the interlayer distance causes optical red-shift on nonlinear optical properties. Therefore, it can be deduced that the suitably chosen interlayer distance can be used to tune optical properties within the infrared spectrum region in optoelectronic devices such as far-infrared photo-detectors, high-speed electronic-optical modulators, and infrared lasers.

Effect of external electric field on photo-responsivity of CdS/ZnSe multiple quantum well photodetector

We show the enhancement of photo-responsivity through applied external electric field F of CdS/ZnSe multiple quantum well (MQW) photo-detector for the detection of mid infrared wavelengths. The subband energy levels E n are calculated using the Schrödinger equation via finite difference method by incorporating exchange-correlation potential and Hartree potential caused by doping in the well layer. We note that by increasing F , E n and the corresponding optical transition energies decreases. It is observed that dipole matrix element M 21 reduces for higher F and we obtain approximately 38 % lower value of M 21 at F = 40 kV/cm. Moreover, absorption coefficient decreases with F due to the strong dependence on M 21 . We obtain current density of 0.03 A/cm 2 and responsivity of 0.012 A/W at wavelength λ = 2.73 μm for M (number of wells) = 20, well width L w = 2 nm at F = 20 kV/cm. We show that the responsivity is enhanced by increasing M, L w as well as doping concentration N D in the well. We also achieved higher photo-responsivity in CdS/ZnSe MQW using our proposed model as compared to the earlier reported results for GaAs/AlGaAs QWIP . • We achieved enhancement of photo-responsivity in CdS/ZnSe QWIP as a function of electric field ( F ). • The Photocurrent ( J ) and Responsivity ( R ) are more significant at higher F . • Enhnacement of J and R with F is due to the reduction in dipole matrix element. • Increasing doping concentrations, number of wells and well widths of QWIP enhances responsivity.