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1.
Based on the framework of effective-mass approximation and variational approach, the luminescent properties are investigated theoretically in self-formed wurtzite GaN/AlxGa1−xN single-quantum dots (QDs). Considering the three-dimensional (3D) confinement of electron and hole pair and the strong built-in electric field effects, the exciton binding energy, the emission wavelength and the oscillator strength are calculated with and without the built-in electric field in detail. The results elucidate that the strong built-in electric field has a significant influence on luminescent properties of GaN/AlxGa1−xN QDs. 相似文献
2.
S.Y. Wei X. Zhao C.X. Xia H.R. Wu F. Zhang W. Li 《Physica E: Low-dimensional Systems and Nanostructures》2006,33(2):343-348
Based on the framework of effective-mass approximation and variational approach, luminescent properties are investigated theoretically in self-formed wurtzite InxGa1−xN/GaN quantum dots (QDs), considering the three-dimensional confinement of electron and hole pair and the strong built-in electric field effects due to the piezoelectricity and spontaneous polarization. The exciton binding energy, the emission wavelength and the oscillator strength as functions of the different structural parameters (the height L and the radius R) are calculated with and without the built-in electric field in detail. The results elucidate that the strong built-in electric field has a significant influence on luminescent properties of InxGa1−xN/GaN QDs. 相似文献
3.
Within the framework of the effective-mass approximation and variational approach, we present calculations of the bound exciton binding energy, due to an ionized donor, in wurtzite InxGa1−xN/GaN strained quantum dots (QDs), considering three-dimensional confinement of the electron and hole in the QDs and the strong built-in electric field induced by the spontaneous and piezoelectric polarizations. Our results show that the position of the ionized donor, the strong built-in electric field, and the structural parameters of the QDs have a strong influence on the donor binding energy. The variation of this energy versus position of the donor ion is in double figures of milli-electron volt. Realistic cases, including the donor in the QD and in the surrounding barriers, are considered. 相似文献
4.
Within the framework of the effective-mass approximation, the exciton states and interband optical transitions in InxGa1−xN/GaN strained quantum dot (QD) nanowire heterostructures are investigated using a variational method, in which the important built-in electric field (BEF) effects, dielectric-constant mismatch and three-dimensional confinement of the electron and hole in InxGa1−xN QDs are considered. We find that the strong BEF gives rise to an obvious reduction of the effective band gap of QDs and leads to a remarkable electron-hole spatial separation. The BEF, QD height and radius, and dielectric mismatch effects have a significant influence on exciton binding energy, electron interband optical transitions, and the exciton oscillator strength. 相似文献
5.
Based on the framework of effective-mass approximation and variational approach, optical properties of exciton are investigated theoretically in ZnO/MgxZn1−xO vertically coupled quantum dots (QDs), with considering the three-dimensional confinement of electron and hole pair and the strong built-in electric field effects. The exciton binding energy, the emission wavelength and the oscillator strength as functions of the structural parameters (the dot height, the barrier thickness between the coupled wurtzite ZnO QDs and Mg content x in the barrier layers) is calculated in detail. The results elucidate that Mg content have a significant influence on the exciton state and optical properties of ZnO coupled QDs. When Mg content x increases, the strong built-in electric field increases and leads to the redshift of the effective band gap of the MgxZn1−xO layer. These theoretical results are useful for design and application of some important photoelectronic devices constructed by using ZnO strained QDs. 相似文献
6.
Based on the framework of effective-mass approximation and variational approach, optical properties of exciton are investigated theoretically in ZnO/MgxZn1−xO vertically coupled quantum dots (QDs), with considering the three-dimensional confinement of electron and hole pair and the strong built-in electric field effects due to the piezoelectricity and spontaneous polarization. The exciton binding energy, the emission wavelength and the oscillator strength as functions of the different structural parameters (the dot height and the barrier thickness between the coupled wurtzite ZnO QDs) are calculated with the built-in electric field in detail. The results elucidate that structural parameters have a significant influence on the exciton state and optical properties of ZnO coupled QDs. These results show the optical and electronic properties of the quantum dot that can be controlled and also tuned through the nanoparticle size variation. 相似文献
7.
(Ga1−xMnx)N/GaN digital ferromagnetic heterostructures (DFHs) and (Ga1−xMnx)N/GaN grown on GaN buffer layers by using molecular beam epitaxy have been investigated. The photoluminescence (PL) spectra showed band-edge exciton transitions. They also showed peaks corresponding to the neutral donor-bound exciton and the exciton transitions between the conduction band and the Mn acceptor, indicative of the Mn atoms acting as substitution. The magnetization curves as functions of the magnetic field at 5 K indicated that the saturation magnetic moment in the (Ga1−xMnx)N/GaN DFHs decreased with increasing Mn mole fraction and that the saturation magnetic moment and the coercive field in the (Ga1−xMnx)N/GaN DFHs were much larger than those in (Ga1−xMnx)N thin films. These results indicate that the (Ga1−xMnx)N/GaN DFHs hold promise for potential applications in spintronic devices. 相似文献
8.
Considering the strong built-in electric field (BEF), dielectric-constant mismatch and 3D confinement of the electron and hole, the exciton states and interband optical transitions in [0 0 0 1]-oriented Ga-rich wurtzite InxGa1−xN/GaN strained quantum dot (QD) nanowire heterostructures are investigated theoretically using a variational approach under the effective mass approximation. We find that the strong BEF gives rise to an obvious reduction of the effective band gap of QDs and leads to a remarkable electron-hole spatial separation. The BEF, QD height and radius, and dielectric mismatch effects have a significant influence on exciton binding energy, electron interband optical transitions, and the radiative decay time. Our calculations show that the radiative decay time of the redshifted transitions is large and increases almost exponentially when the QD height increases, which is in good agreement with the previous experimental and theoretical results. 相似文献
9.
Within the framework of effective mass approximation, the binding energy of a hydrogenic donor impurity in zinc-blende GaN/AlxGa1−xN spherical quantum dot (QD) is investigated using the plane wave basis. The results show that the binding energy is highly dependent on impurity position, QD size, Al content and external field. The binding energy is largest when the donor impurity is located at the centre of the QD and the binding energy of impurity is degenerate for symmetrical positions with respect to the centre of QD without the external electric field. The maximum of the donor binding energy is shifted from the centre of QD and the degenerating energy levels for symmetrical positions with respect to the centre of QD are split in the presence of the external electric field. The binding energy is more sensitive to the external electric field for the larger QD and lower Al content. In addition, the Stark shift of the binding energy is also calculated. 相似文献
10.
The Shubnikov-de Haas (S-dH) results at 1.5 K for AlxGa1−xN/AlN/GaN heterostructures and the fast Fourier transformation data for the S-dH data indicated the occupation by a two-dimensional electron gas (2DEG) of one subband in the GaN active layer. Photoluminescence (PL) spectra showed a broad PL emission about 30 meV below the GaN exciton emission peak at 3.474 eV that could be attributed to recombination between the 2DEG occupying in the AlN/GaN heterointerface and photoexcited holes. A possible subband structure was calculated by a self-consistent method taking into account the spontaneous and piezoelectric polarizations, and one subband was occupied by 2DEG below the Fermi level, which was in reasonable agreement with the S-dH results. These results can help improve understanding of magnetotransport, optical, and electronic subband properties in AlxGa1−xAs/AlN/GaN heterostructures. 相似文献
11.
Based on the effective-mass approximation, the donor binding energy in a cylindrical zinc-blende (ZB) symmetric InGaN/GaN coupled quantum dots (QDs) is investigated variationally in the presence of an applied electric field. Numerical results show that the ground-state donor binding energy is highly dependent on the impurity positions, coupled QDs structure parameters and applied electric field. The applied electric field induces an asymmetric distribution of the donor binding energy with respect to the center of the coupled QDs. When the impurity is located at the center of the right dot, the donor binding energy has a maximum value with increasing the dot height. Moreover, the donor binding energy is the largest and insensitive to the large applied electric field (F?400 kV/cm) when the impurity is located at the center of the right dot in ZB symmetric In0.1Ga0.9N/GaN coupled QDs. In addition, if the impurity is located inside the right dot, the donor binding energy is insensitive to large middle barrier width (Lmb?2.5 nm) of ZB symmetric In0.1Ga0.9N/GaN coupled QDs. 相似文献
12.
在有效质量近似下,考虑强的内建电场和应变对材料参量的影响,变分研究了流体静压力对有限高势垒应变纤锌矿GaN/Al0.15Ga0.85N柱形量子点中重空穴激子的结合能、发光波长和电子空穴复合率的影响.数值结果表明,激子结合能和电子空穴复合率随流体静压力的增大而近线性增大,发光波长随流体静压力的增大而单调减小.在量子点尺寸较小的情况下,流体静压力对激子结合能和电子空穴复合率的影响更明显.由于应变效应,为了获得有效的电子-空穴复合过程,GaN量子点的高度必须小于5.5 nm. 相似文献
13.
(Ga1−xMnx)N thin films grown on GaN buffer layers by using molecular beam epitaxy were investigated with the goal of producing diluted magnetic semiconductors (DMSs) with band-edge exciton transitions for applications in optomagnetic devices. The magnetization curve as a function of the magnetic field at 5 K indicated that ferromagnetism existed in the (Ga1−xMnx)N thin films, and the magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature of the (Ga1−xMnx)N thin film was above room temperature. Photoluminescence and photoluminescence excitation spectra showed that band-edge exciton transitions in (Ga1−xMnx)N thin films appeared. These results indicate that the (Ga1−xMnx)N DMSs with a magnetic single phase hold promise for potential applications in spin optoelectronic devices in the blue region of the spectrum. 相似文献
14.
《Superlattices and Microstructures》2000,27(1):53-58
Interband transitions of pseudomorphic GaN/AlxGa1 − xN quantum wells are analysed theoretically with respect to the piezoelectric field utilizing a 6 × 6 Rashba–Sheka–Pikus (RSP) Hamiltonian. Band structure modifications due to the built-in Stark effect explain a shift of the emission peak in GaN/Al0.15Ga0.85N of up to 400 meV. Quantum well exciton binding energies are calculated by the variational method and are discussed in terms of spatial separation of electrons and holes by the built-in electric field, as well as the interaction between valence subbands. 相似文献
15.
Tunneling induced electron transfer in SiNx/AlGaN/GaN based metal-insulator-semiconductor structures
M.J. Wang Y. Wang S. Huang F.J. Xu J. Xu Z.X. Qin Z.J. Yang G.Y. Zhang 《Physics letters. A》2007,371(3):249-253
Tunneling induced electron transfer in SiNx/Al0.22Ga0.78N/GaN based metal-insulator-semiconductor (MIS) structures has been investigated by means of capacitance-voltage (C-V) measurements at various temperatures. Large clock-wise hysteresis window in C-V profiles indicates the injection of electrons from the two-dimensional electron gas (2DEG) channel to the SiNx layer. Depletion of the 2DEG at positive bias in the negative sweeping direction indicates that the charges injected have a long decay time, which was also observed in the recovery process of the capacitance after injection. The tunneling induced electron transfer effect in SiNx/Al0.22Ga0.78N/GaN based MIS structure opens up a way to design AlxGa1−xN/GaN based variable capacitors and memory devices. 相似文献
16.
《Superlattices and Microstructures》2005,38(3):161-167
We have calculated the spectral regime of subband transitions in AlxGa1−xN/GaN and AlxGa1−xN/InN single quantum wells. We used a simplified model to account for the internal electric fields, which modify the shape of the quantum well. Some of the parameters for these materials have not yet been firmly established. Therefore, we carried out the analysis for the extremes of the reported values of conduction band discontinuities and band gaps (in the case of InN). This analysis shows that the spectral regime of interband transitions for 1–4 nm thick wells has wavelengths above 0.5 μm for AlGaN/InN and above 0.8 μm for AlGaN/GaN and both heterostructures cover several μm wavelengths. The spectral variation with alloy composition is less pronounced in the AlxGa1−xN/InN single quantum wells due to the higher electric field present across the InN quantum well as compared to GaN. The results of these calculations are in good agreement with more rigorous theoretical approaches and available experimental values for AlxGa1−xN/GaN. 相似文献
17.
The effects of the In-mole fraction (x) of an InxGa1−xN back barrier layer and the thicknesses of different layers in pseudomorphic AlyGa1−yN/AlN/GaN/InxGa1−xN/GaN heterostructures on band structures and carrier densities were investigated with the help of one-dimensional self-consistent solutions of non-linear Schrödinger-Poisson equations. Strain relaxation limits were also calculated for the investigated AlyGa1−yN barrier layer and InxGa1−xN back barriers. From an experimental point of view, two different optimized structures are suggested, and the possible effects on carrier density and mobility are discussed. 相似文献
18.
H. Takeuchi Y. Yamamoto Y. Kamo T. Oku M. Nakayama 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):311-314
We have investigated electric field strengths in the AlxGa1-xN layer, FAlGaN's, of AlxGa1-xN/GaN heterostructures with and without a GaN cap layer using photoreflectance (PR) spectroscopy. Franz-Keldysh oscillations
(FKOs) from the AlxGa1-xN layer are clearly observed in the PR spectra. It is found from analysis of the FKOs that stacking of the cap layer causes
a remarkable enhancement of FAlGaN. This fact demonstrates that the FKO profile is a non-destructive probe for a change of built-in electric field strength
induced by a cap layer. Numerical calculations of FAlGaN based on a Schr?dinger-Poisson equation clarify that the magnitude of the enhancement of FAlGaN is dominated by the cap-layer thickness. 相似文献
19.
Semiconductor optoelectronic devices based on GaN and on InGaN or AlGaN alloys and superlattices can operate in a wide range of wavelengths, from far infrared to near ultraviolet region. The efficiency of these devices could be enhanced by shrinking the size and increasing the density of the semiconductor components. Nanostructured materials are natural candidates to fulfill these requirements. Here we use the density functional theory to study the electronic and structural properties of (10,0) GaN, AlN, AlxGa1 − xN nanotubes and GaN/AlxGa1 − xN heterojunctions, 0<x<1. The AlxGa1 − xN nanotubes exhibit direct band gaps for the whole range of Al compositions, with band gaps varying from 3.45 to 4.85 eV, and a negative band gap bowing coefficient of −0.14 eV. The GaN/AlxGa1 − xN nanotube heterojunctions show a type-I band alignment, with the valence band offsets showing a non-linear dependence with the Al content in the nanotube alloy. The results show the possibility of engineering the band gaps and band offsets of these III-nitrides nanotubes by alloying on the cation sites. 相似文献
20.
A. Wolos Z. Wilamowski C. SkierbiszewskiA. Drabinska B. LucznikI. Grzegory S. Porowski 《Physica B: Condensed Matter》2011,406(13):2548-2554
We discuss problem of Rashba field in bulk GaN and in GaN/AlxGa1−xN two-dimensional electron gas, basing on results of X-band microwave resonance experiments. We point at large difference in spin-orbit coupling between bulk material and heterostructures. We observe coupled plasmon-cyclotron resonance from the two-dimensional electron gas, but no spin resonance, being consistent with large zero-field spin splitting due to the Rashba field reported in the literature. In contrast, small anisotropy of g-factor of GaN effective mass donors indicates rather weak Rashba spin-orbit coupling in bulk material, not exceed 400 G, αBIA<4×10−13 eVcm. Furthermore, we observe new kind of electron spin resonance in GaN, which we attribute to surface electron accumulation layer. We conclude that the sizable Rashba field in GaN/AlxGa1−xN heterostructures originates from properties of the interface. 相似文献