In this paper, the second and third harmonic generation (SHG and THG) in nonlinear optics of AlxIn1−xAs/InyGa1−yAs double-quantum-well structures (DQWs) has been numerically studied. The energy eigenvalues and the corresponding eigenfunctions were determined using effective mass and parabolic band approximations. The nonlinear optical properties of AlxIn1−xAs/InyGa1−yAs DQWs are closely related to their electronic structure and external field responses. The application of an external electric field induces asymmetric distortions to the potential profile of DQWs, which may enhance the dipole matrix elements between subbands compared to single-quantum-well structures. The results reveal that the position and amplitude of the SHG and THG coefficients can be effectively altered by modifying the external electric field and the geometrical parameters. Variations in the width and indium composition of the main well of DQWs have different impacts on the SHG and THG: Narrower well width and lower indium composition enhance SHG, but weaken THG. Additionally, higher indium composition induces blueshifts in SHG and THG. These findings highlight the potential for tailoring the SHG and THG characteristics of AlxIn1−xAs/InyGa1−yAs DQWs by adjusting the quantum well width and applying external electric fields. Such tunability is crucial for the development of advanced optoelectronic devices with customized nonlinear optical properties.

This study systematically investigates the spontaneous emission spectra of GaAs1-xBix/GaAs double quantum wells (DQWs) through an eight-band k•p model, elucidating the dependence of the emission characteristics across varying well widths, barrier thicknesses, Bi compositions, doping densities, and temperatures. The emission peak intensity decreases and redshifts with increasing well-width due to weakened quantum confinement, with DQWs showing a more gradual intensity decay than SQWs. The GaAs barrier thickness of the DQWs is found to affect minimally the spontaneous emission spectra, but a GaAs0.95Bi0.05/GaAs DQW, where the interwell barrier is a GaAs0.99Bi0.01 barrier layer, demonstrates the tunability of the emission intensity with varying barrier thickness. Varying the Bi composition in the GaAs1-xBix wells of the DQWs shows invariant peak intensity across low compositions (0.01–0.05) and a pronounced redshift over 30 meV. On the other hand, simultaneous variation of Bi compositions in both wells enables a monotonic redshift. This shows a method to realize a broadband frequency tunability. A thicker interwell GaAs1-xBix barrier layer, for a specified Bi composition, can result in a relatively larger redshift. Increased carrier density boosts peak intensity. As the temperature increases, the peak intensity decreases, and the peak position undergoes a redshift. Notably, DQWs exhibit slower decay rates at high energies compared to SQWs. Furthermore, under equivalent confinement conditions, DQWs demonstrate superior emission rates relative to SQWs.

The relaxation dynamics of photoexcited carriers of CdTe is vital toward its applications in high-performance optoelectrical devices. In this paper, the dependences of transient drift velocities of photoexcited electrons in bulk CdTe on photoexcitation conditions such as the pump intensity and photoexcitation wavelengths, temperature and externally applied electric field, are systematically investigated by the ensemble Monte Carlo method (EMC). The main scattering mechanisms including nonelastic deformation potential acoustic phonon, deformation potential optical phonon scattering, ionized impurity (II) scattering, and polar optical phonon scattering events, the effects of nonequilibrium phonons, and the Pauli exclusion principle are considered in EMC. The velocity overshoot phenomenon is only found to arise at a low temperature (100 K), with a longer photoexcitation wavelength (640 nm) and under a higher electric field (> 50 kV/cm). The effect of nonequilibrium phonons on electron drift velocity is found to be dependent on the photoexcited carrier density. Our findings may be useful for designing novel CdTe-based optoelectronic devices, which employ nonequilibrium photoexcited carriers to improve the performance.

In this work, electron transport in Mg x Zn 1− x O/ZnO heterostructures at room temperature is simulated by the ensemble Monte Carlo (EMC) method. Electron scattering mechanisms including acoustic deformation potential, piezoelectric acoustic phonon, polar optical phonon (POP), interface roughness (IFR), dislocation, electron escape (ESC) and capture (CPR) by optical phonons, and random alloy are considered in EMC. The electron drift velocity in Mg x Zn 1− x O/ZnO heterostructures is calculated for various Mg mole fractions x (0.1–0.3) at electric fields up to 25 kV/cm. We find that no obvious velocity saturation occurs in the range of the electric field considered. The results show that ESC scattering is one of the main physical mechanisms limiting the drift velocity. On the other hand, the competition between IFR and intersubband POP scattering is found to play an important role in the change in electron drift velocity with the increasing Mg mole fractions.

Terahertz (THz) intersubband absorption spectra in the Mg x Zn 1−x O/ZnO step quantum wells (SQWs) at the temperature of 77 K have been numerically studied. Electron scatterings, including piezoelectric acoustic phonon, polar optical phonon, interface roughness (IFR), random alloy (RAS), and ionized impurity (II) scatterings, are considered to analyze the lineshape broadening. Wherein IFR and RAS are found to be the main lineshape-broadening mechanisms. By changing the well width of SQWs, SQWs with the three-energy level structure can realize THz intersubband absorption spectra in a wide frequency range. In order to obtain the relatively stronger THz intersubband absorption from subband 0 to 2 in SQWs, the corresponding well width should be large enough (~ 15 nm). The varying of step barrier thickness can not obviously change the THz intersubband absorption from subband 0 to 1. THz intersubband absorption frequency can be continuously tuned by changing the Mg composition in the outer and step barrier layers. Finally, it is found that doping in the outer and step barrier layers gives rise to completely different frequency shifts of THz intersubband absorption: the increasing doping densities in the outer barrier layer induces blueshifts, and that in the step barrier layer induces redshifts. This work provides an idea for the future development of THz detectors based on Mg x Zn 1−x O materials.

The drift velocity of photo-generated electrons in CdTe by lasers with wavelengths of 532, 355, and 266 nm is studied by the Monte Carlo method. The effects of laser wavelengths on the electron drift velocity are systematically investigated under various laser fluxes, doping densities, and temperatures. It is found that the drift velocity as a function of electric field v_d(E) has a close relationship with the laser wavelengths: the electron drift velocity in CdTe becomes larger when a longer photoexcitation wavelength is used. On the other hand, the doping effect, as well as the effect of the laser energy flux, on the v_d(E) dependence demonstrates different characteristics for different laser wavelengths. The difference in electron drift velocity caused by the various wavelengths reduces with increasing temperatures. In the case of a low laser energy flux, doping in CdTe plays a remarkable role in v_d(E) relations. These new results are helpful in understanding the microscopic mechanism of relaxation processes of photo-excited carriers and applications of CdTe-based optoelectronic devices.

GaAsBi/GaAs heterojunctions have a type II band arrangement, and the band structure energy of GaAs alloys with diluted Bi content provides a wide range for designing effective band gaps. In this paper, we calculate the electronic energy band structure of GaAsBi/GaAs quantum wells (QWs) with different Bi concentrations under the 8-band K · P model. The calculated results show that the Bi concentration has a great influence on the band gap, valence band, conduction band, and other structures of GaAsBi/GaAs QWs. Based on the band structure, we make systematical simulations on the effects of different quantum well widths, different Bi concentrations, different carrier densities, and different temperatures on the spontaneous emission spectra (SES) of GaAsBi/GaAs QWs. We find that the peaks of SES reduce with the increase of temperature and well width of the quantum well structure. The full width at half maximum (FWHM) of SES at 300 K is 0.1 eV, which is much broader than that at 100 K. The increasing Bi concentration is found to give rise to the blue shift of SES. Finally, the carrier concentration in the quantum well is found to be an important factor that can enhance the SES peak values. The findings in this work are helpful in the design of GaAsBi/GaAs-based optoelectronic devices.

In this work, electron transport in Mg x Zn 1− x O/ZnO heterostructures at room temperature is simulated by the ensemble Monte Carlo (EMC) method. Electron scattering mechanisms including acoustic deformation potential, piezoelectric acoustic phonon, polar optical phonon (POP), interface roughness (IFR), dislocation, electron escape (ESC) and capture (CPR) by optical phonons, and random alloy are considered in EMC. The electron drift velocity in Mg x Zn 1− x O/ZnO heterostructures is calculated for various Mg mole fractions x (0.1–0.3) at electric fields up to 25 kV/cm. We find that no obvious velocity saturation occurs in the range of the electric field considered. The results show that ESC scattering is one of the main physical mechanisms limiting the drift velocity. On the other hand, the competition between IFR and intersubband POP scattering is found to play an important role in the change in electron drift velocity with the increasing Mg mole fractions.

Citrate salts (CSs), as one type of organic salts, have been widely used in the food and pharmaceutical industries. Accurate and quantitative detection of CSs in food and medicine is very important for health and safety. In this study, an asymmetric double-opening ring metamaterial sensor is designed, fabricated, and used to detect citrate salts combined with THz spectroscopy. Factors that influence the sensitivity of the metamaterial sensor including the opening positions and the arrangement of the metal opening ring unit, the refraction index and the thickness of the analyte deposited on the metamaterial sensor were analyzed and discussed from electromagnetic simulations and THz spectroscopy measurements. Based on the high sensitivity of the metamaterial sensor to the refractive index of the analyte, six different citrate salt solutions with low concentrations were well identified. Therefore, THz spectroscopy combined with a metamaterials sensor can provide a new, rapid, and accurate detection of citrate salts.

In this work, the electron mobility in the MgZnO/ZnO heterostructure at room temperature is theoretically studied by considering interface roughness (IFR), dislocation (DIS), and polar optical phonon (POP) scattering. Analytical formulae are introduced to calculate the critical thickness and dislocation density in the barrier layer of MgZnO/ZnO heterostructures. The calculated critical thickness for the MgZnO/ZnO heterostructure is much smaller than that for the AlGaN/GaN heterostructure system. At room temperatures, POP scattering is found to be the most important scattering mechanism. On the other hand, the change of electron mobility limited by IFR as a function of the barrier thickness in the MgZnO layer is found to be quite different to that limited by DIS. High-density (>1013cm−2) 2DEG can be obtained in the MgZnO/ZnO interface by increasing the thickness and Mg composition in the MgZnO layer.

The main work of this paper is to combine the advantages of Finite Element Method (FEM) and Monte Carlo (MC) method in semiconductor numerical modeling and calculation, and develop and design a semiconductor numerical calculation software based on the combination of FEM and MC method. It mainly includes a complete set of semiconductor numerical calculation tools, such as mesh discrete module, partial differential equation (PDE) module, MC module and visualization (VTK) module. Different from the general MC method, the Poisson equation coupling solution module in the MC method is solved by the FEM, which can adapt to various irregular discrete calculations. The device discretization can be optimized according to the actual needs, so that relatively accurate calculation results can be obtained while consuming less resources.

The linear intersubband optical absorption spectra in MgZnO/ZnO triple quantum wells (TQWs) are theoretically calculated with various geometrical structures and material compositions. Mg composition is found to have remarkable effects on peak position and magnitude of linear optical absorption spectra (OAS). The width of the potential well in which subband 1 is located can also significantly influence the linear OAS, but there is no influence found from the variation of other potential well width and barrier thickness. On the other hand, the effect of electric field transversely applied across MgZnO/ZnO TQWs on the energy of subbands and OAS are analyzed. This study suggests several methods to obtain tunable intersubband optical absorption in MgZnO/ZnO TQWs which can be potentially used as infrared detector devices.

The energy level structures of MgxZn1−xO/ZnO/MgxZn1−xO quantum wells (QWs) with various geometrical structures and material compositions are obtained. Terahertz (THz) intersubband absorption can be realized and tunable with x in the range of 0.01~0.04 and well width in the range of 5~13 nm. Electron scattering such as piezoelectric acoustic phonon (PAP), polar optical phonon (POP), interface roughness (IFR), and random alloy (RAS) scattering are included in the calculations to analyze the linewidth broadening. Increasing the Mg composition or decreasing the well width can obtain high-frequency THz intersubband absorption, in which case IFR is found to be the physical mechanism that makes the linewidth broaden. On the other hand, the influence difference of PAP scattering for the lower Mg composition, which may be caused by the different electro-mechanical coupling coefficients (EMCC), is obviously larger than that for the higher Mg composition, meaning that the accurate value of EMCC is much more important for the THz intersubband absorption in MgxZn1−xO/ZnO/MgxZn1−xO QWs with a smaller x. The findings are helpful in the design of THz detector devices.

目前的三维虚拟仿真研究都集中于引入AR、VR技术使仿真更加沉浸、体验更好上,但对于在进行仿真实验过程中学生能够自主学习并在学习后考察学生的学习情况的研究还相对欠缺.基于这个原因,该研究利用贝叶斯网络设计了智能学习模块.根据学生自主学习的情况,动态更新对应学生的贝叶斯网络模块.学生在学习实验原理后,系统根据实验文档和已有的贝叶斯网络模块给出有针对性的习题来考察学生的学习情况,利用贝叶斯网络构建的知识网引导学生巩固对仿真实验的原理学习.基于贝叶斯网理论,把领域知识按知识项进行划分,然后在这些知识项之间建立依赖关系以确定贝叶斯网络的因果推理关系.这种方式在学习系统中起着重要的作用,为学生提供个性化的学习帮助,使学习材料适应学生的能力方面发挥了一定的作用.

A new photoresponsive bent-core nematic (BCN) material, which exhibits flexoelectric domains (FDs) driven by electric field, is reported. Unexpectedly, it is found that the morphologies of FDs can be controlled by irradiation with light fields. This light tunability is ascribed to the photoisomerization effect of the azo moiety within the BCN molecules, where the ratio of trans and cis isomers changes according to the parameters of the light field, resulting in adjustable electric threshold and periodicity of FDs. Based on this principle, a prototype of controllable optical grating is assembeled, whose operation can be manipulated by the wavelength or intensity of light. Due to the easy, instant, and remote operation by light, this optical, contactless tunability has a great advantage over traditional electric control in tunable photonic devices.

Two dimensional electron gas (2DEG) transports in In0.53Ga0.47As/In0.52Al0.48As multilayer structure (MLS) illuminated by an ultrashort optical pulse with the central wavelength at 1.55 mu m is investigated by ensemble Monte Carlo simulations. Terahertz (THz) pulses are calculated according to the transient photocurrent in the InGaAs layers. It is found that InGaAs/InAlAs MLS with narrower InGaAs layers has an advantage in generating large temporal change in the transient photocurrent, which thereby is able to increase the intensity of THz emission. Beryllium (Be)-doping in InGaAs layers provides a scattering channel to speed the decay of photocurrent, and is shown to be a factor in shaping the bipolar structure of THz temporal waveforms. Bandwidth of the generated THz emission is found to be mainly controlled by the laser pulse duration at low doping level, but at high doping level, the bandwidth is determined together by laser pulse duration and doping density.

In this paper, the energy levels and the wave functions of the Schrodinger equation with position-dependent mass are theoretically deduced, and they are brought into nonlinear optical third-harmonic generation. We find that the peak of the third-harmonic coefficient becomes larger and a blueshift occurs under the condition of variable mass. Moreover, with the increment of mass variable k, the energy interval E-ij decreases, which makes the coefficients suffer a redshift, and the absolute value of the matrix elements product vertical bar M12M23M34M41 vertical bar presents different monotonicity, which makes the peak value of the coefficient change regularly. (C) 2018 Optical Society of America

In this paper, the energy levels and the wave functions of the schrödinger equation with position-dependent mass (PDM) are theoretically deduced, and they are brought into the nonlinear optical rectification (OR) and the second harmonic generation (SHG). We find that the peaks of coefficient curves of optical rectification and second harmonic generation become larger and occur blue shift under the condition of variable mass. Moreover, with the increment of mass variable k, the energy interval Eij decreases, which makes the coefficients suffer a red shift, and the absolute value of the matrix elements product |MijMjkMki| presents different monotonicity, that makes the peaks value of coefficients change regularly.

The linear and nonlinear intersubband optical absorption coefficients (OACs) of nonpolar AlGaN/GaN step quantum well structures (SQWs) were calculated theoretically for various geometrical structures, \( \delta \) doping schemes, and material compositions. The results revealed that the absorption frequency of such structures is obviously tunable by changing parameters such as the quantum well width, step barrier width, Al composition in the step barrier layer, and doping position. These characteristics can be attributed to non-polarization-related effects. The doping and Al composition were found to have remarkable effects on the position and magnitude of the peaks in the nonlinear optical absorption spectrum, whereas the geometric parameters of the SQWs, such as the well width and step barrier width, changed the magnitude of the peaks only very slightly. On the other hand, the nonlinear OACs of the SQWs were found to be strongly sensitive to the Al composition x and doping density in the step barrier layer. This study suggests that the step barrier layer in SQWs plays an important role in manipulating their intersubband optical absorption.

Nonlinear optical refractive index changes (RICs) with polaron effects are studied in this Letter. The energy levels and wave functions of the polaron Schrödinger equation are calculated and brought into the nonlinear RICs to analyze the difference between the effects of the presence and absence of polarons, as well as the specific representation of RICs with polarons.