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1.
Low-temperature photoluminescence measurements were performed on InAsP/InP strained quantum wells grown on InP (lll)B substrates
by gas-source molecular beam epitaxy. The emission energy was observed to increase as the pump-power density increased. This
was attributed to the screening of the internal piezoelectric field by photo-generated carriers. The energy shift was as large
as 35 meV for an InAs0.28P0.72/InP quantum well with a lattice mismatch of ~0.9%. A similar structure with a smaller strain showed saturation of the energy
shift with increasing pump-power density. We performed a model calculation which includes the quantum confined Stark effect,
and this saturation was correlated with a flat-band structure of the quantum well due to the nearly complete screening of
the built-in electric field. 相似文献
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《Microelectronics Journal》2002,33(7):583-588
We report on the optical properties and carrier kinetics of a set of InAs self-assembled quantum dots on (N11)A/B GaAs substrates by means of cw and time-resolved PL. The cw-PL spectra show a blue shift of the PL band on different (N11) QD structures when increasing the carrier photoinjection. This is attributed to a photoinduced screening of the quantum confined Stark shift of the QD optical transition due to a large built-in electric field. The presence of an internal electric field also induces intrinsic optical non-linearity in time-resolved measurements. The analysis of the recombination kinetics shows that the carrier screening occurs inside the QDs, thus demonstrating the intrinsic nature of the built-in field. The dependence of the internal field on the substrate orientation and termination agrees with the presence of piezoelectric field and permanent dipole moment inside the QDs. 相似文献
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Brown I. H. Blood P. Smowton P. M. Thomson J. D. Olaizola S. M. Fox A. M. Parbrook P. J. Chow W. W. 《Quantum Electronics, IEEE Journal of》2006,42(12):1202-1208
We have measured the time response of the emission spectra of In 0.07Ga0.93N quantum wells with widths of 2, 3, and 4nm in GaN following pulsed optical excitation. We observe a blue shift of the emission peak during the excitation and a subsequent red shift as the carriers recombine in the 3- and 4-nm wells, and a negligible shift for the 2-nm well. Using a comprehensive theory we are able to fit both the time evolution of the peak emission energy and the integrated emission intensity. The shift of the emission peak (by about 17 meV) arises from the balancing of the change in screening of the internal piezoelectric field as the carrier density changes and bandgap renormalization. We have projected the calculations to quantify the degree of screening at typical threshold carrier densities. At transparency we estimate carrier densities of 4.3times1016 m-2 and 4.8times1016 m-2 for the 4- and 3-nm wells, respectively, which reduce the internal piezoelectric field in the well to 0.97times108 (4 nm) and 1.03times10 8 (3 nm) Vmiddotm-1 compared with the unscreened value of about 1.23times108 Vmiddotm-1. Thus, a substantial field remains in these wells under laser conditions. We find that this partially screened field is beneficial in reducing the threshold current compared with that of a square well for modal gains up to about 150 cm-1 相似文献
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The theoretical calculation of the electronic structure of any constituent materials is the first step toward the interpretation and understanding of experimental data and reliable device design. This is essentially true for nanoscale devices where both the atomistic granularity of the underlying materials and the quantum-mechanical nature of charge carriers play critical roles in determining the overall device performance. In this paper, within a fully atomistic and quantum-mechanical framework, we investigate the electronic structure of wurtzite InN quantum dots (QDs) self-assembled on GaN substrates. The main objectives are threefold: 1) to explore the nature and the role of crystal atomicity, strain field, and piezoelectric and pyroelectric potentials in determining the energy spectrum and the wave functions; 2) to address the redshift in the ground state, the symmetry lowering and the nondegeneracy in the first excited state, and the strong band mixing in the overall conduction-band electronic states, which is a group of interrelated phenomena that has been revealed in recent spectroscopic analyses; and 3) to study the size dependence of the internal fields and its impact on the electronic structure as a whole. We also demonstrate the importance of 3-D atomistic material representation and the need for using realistically extended substrate and cap layers (multimillion-atom modeling) in studying the built-in structural and electric fields in these reduced dimensional QDs. The models used in this study are as follows: 1) valence-force-field Keating model for atomistic strain relaxation; 2) 20-band nearest neighbor sp 3 d 5 s* tight-binding model for the calculation of single-particle energy states; and 3) microscopically determined polarization constants in conjunction with an atomistic 3-D Poisson solver for the calculation of piezo- and pyroelectric contributions. 相似文献
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V. Krieger W. Wondrak A. Dehbi W. Bartel Y. Ousten B. Levrier 《Microelectronics Reliability》2006,46(9-11):1926-1931
Cracks in Multilayer Capacitors are often latent defects, which are not recognized in production, but can cause substantial problems in field. Therefore it is important to find possibilities to detect those candidates before delivering electronic equipment.In this work, cracked capacitors were characterized by electrical parameter testing and by piezoelectric spectroscopy. As a new method, sound emission spectroscopy was employed as indicator for latent defects and correlated with electrical data and physical analysis. The results show that sound emission used on a statistical basis and piezoelectric response might be effective to screen latent defects in electronic control units. 相似文献
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The specific features of the tunneling current in wurtzite GaN/AlGaN(0001) two-barrier structures are studied by solving the Schrödinger equation and the Poisson equation simultaneously, with regard to spontaneous and piezoelectric polarizations. It is shown that the internal fields manifest themselves in the asymmetry of the tunneling current via the value of the electronic charge in the quantum well. This charge is larger when the internal and external fields in the well compensate each other, resulting in smaller shifts of potential and resonance levels in the active region with voltage, in the higher resistance of the structure, and in the linear current-voltage dependence within a wide range of voltages. When the internal and external fields are the same, the current exhibits a sharp negative-differential-conductivity structure, with the peak-to-valley ratio equal to about four. The structure is similar to one of the branches of the current-voltage characteristic of the GaAs/AlGaAs(001) two-barrier structure, suggesting that nitrides are promising materials for resonance-tunneling devices. 相似文献
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以有限元分析法为理论基础并搭配ANSYS软件,建立圆盘式压电双晶片振子的模型,研究压电振子半径、压电层厚度和支撑层厚度对其发电能力的影响。并在此基础上探讨压电-电路的导纳阻抗及输出功率特性。着重研究压电双晶片在串联和并联两种连接方式之间的差异。研究结果表明,在保证可靠度和固有频率的前提下,应尽量增加压电振子半径,减小振子的基板厚度,以获得最大的输出电压。串联方式的输出电压大,内部阻抗高,适用于后续负载阻抗较高的能量采集系统;并联方式的内部阻抗较串联式低,适用于后续负载阻抗适中的能量采集系统。而当在两种电路连接方式下的外部电阻达到最佳电阻值时,两者最佳输出功率相同。 相似文献
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An Improved Calculation Model for Analysis of [111] InGaAs/GaAs Strained Piezoelectric Superlattices
We present a calculation model for an improved quantitative theoretical analysis of electronic and optical properties of strained-piezoelectric [111] InGaAs/GaAs superlattices (SLs). The model includes a full band-coupling between the four important energy bands: conduction, heavy, light, and spin split-off valence bands. The interactions between these and higher lying bands are treated by the k · p perturbation method. The model takes into account the differences in the band and strain parameters of constituent materials of the heterostructures by transforming it into an SL potential in the larger band-gap material region. It self-consistently solves an 8 · 8 effective-mass Schrödinger equation and the Hartree and exchange-correlation potential equations through the variational procedure proposed recently by the present first author and applied to calculate optical matrix elements and spontaneous emission rates. The model can be used to further elucidate the recent theoretical results and experimental observations of interesting properties of this type of quantum well and SL structures, including screening of piezoelectric field and its resultant optical nonlinearities for use in optoelectronic devices. 相似文献
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Temporal variations of the photoluminescence (PL) peak wavelength due to screening of the piezoelectric field by photogenerated carriers are observed in ln0·2Ga0·8As/GaAs single quantum wells grown on (n11)A-oriented substrates (n=1, 2, 3) by using time-resolved PL spectroscopy. The partial screening of the piezoelectric field shifts the PL peak to shorter wavelengths. The subsequent decrease of the photogenerated carriers by recombination produces a redshift of the PL peak, which is explained using a model that fits successfully the experimental results. 相似文献
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A resonant helical coil antenna-like structure has been explored for wireless excitation of piezoelectric devices. The basic idea behind this wireless excitation of piezoelectric device is electromagnetic resonance along with piezoelectric resonance. The analytical studies reveal that the maximum excitation occurs in the piezoelectric device when the operating frequency of the system coincides with its mechanical resonant frequency. It has been seen that the intensity of piezoelectric stimulation depends on the frequency of operation, air gap, relative position, electric load, and the generated electric field strength by the helical coil antenna-like structure. The analytical results are verified with the measured experimental results, and are found to be in well agreement. By adopting this proposed wireless excitation system the free actuation of the piezoelectric devices can be enabled as opposed to the confined motion for various potential applications. 相似文献
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Bonnail N. Tonneau D. Jandard F. Capolino G.-A. Dallaporta H. 《Industrial Electronics, IEEE Transactions on》2004,51(2):354-363
Scanning probe microscopes are now widely used in the field of material science and engineering for surface imaging at atomic scale. Their principle is based on the surface probing by a sharp tip approached at a nanometric distance of the surface. The probe is fixed to piezoelectric actuators allowing its displacement above the surface. An electronic command of a scanning tunneling microscope (STM) has been designed and tested. The regulation feedback loop of the tunnel current includes an integral controller, as is the case in commercial equipment. An extra control by variable-structure system has been implemented on this electronic command. Its principle is based on the commutation of the feedback sign. The effect on the system performance of the variable structure control is presented and discussed. An STM head has been modeled and all the model parameters have been determined. The model has been validated by comparison of the experimental and simulated responses of the system under excitation. 相似文献
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压电叠堆的内部应力场是影响其可靠性的主要因素之一。基于COMSOL Multiphysics有限元软件,建立了精细尺度的压电叠堆有限元计算模型,通过理论分析验证了模型的准确性。对比分析了不同电极构型、陶瓷层厚度以及有无过渡段等细观结构特性对叠堆内部应力场的影响。结果表明,两种电极构型压电叠堆的内部都存在应力集中现象,叉指电极型叠堆的最大应力集中值远高于全电极;改变陶瓷层的厚度不影响叠堆内部应力集中的分布位置,最大切向应力随厚度的增大而减小,最大法向应力随厚度增大而增大;设置过渡段陶瓷可以有效地减少过渡部位活性陶瓷的最大应力集中值,增强压电叠堆的可靠性。 相似文献
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Eight-band k.p theory including strain and piezoelectric effects are employed to calculate the strain distribution and electron and hole energy levels of InAs/GaAs quantum dots grown on [11k] substrates in the presence of an external magnetic field. Height of the dot determines how the increasing of k influences isotropic part of the strain tensor while biaxial part of the strain tensor is always reduced with increasing k. Because of the reduced symmetry of high index surfaces, influence of piezoelectric effect on the electronic structure becomes more dominant with increasing k. Electron energy levels are influenced by the isotropic part of the strain compared to the hole energy levels, where strong heavy hole–light-hole mixing is observed. For the dots grown on the [11k] surfaces magnetic field has smaller influence on the electron and hole energy levels as compared to the referent case. 相似文献
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