首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
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   

2.
Based on effective-mass approximation, we present a three-dimensional study of the exciton in GaN/AlxGa1−xN vertically coupled quantum dots (QDs) by a variational approach. The strong built-in electric field due to the piezoelectricity and spontaneous polarization is considered. The relationship between exciton states and structural parameters of wurtzite GaN/AlxGa1−xN coupled QDs is studied in detail. Our numerical results show that the strong built-in electric field in the GaN/AlxGa1−xN strained coupled QDs leads to a marked reduction of the effective band gap of GaN QDs. The exciton binding energy, the QD transition energy and the electron-hole recombination rate are reduced if barrier thickness LAlGaN is increased. The sizes of QDs have a significant influence on the exciton state and interband optical transitions in coupled QDs.  相似文献   

3.
We report photoluminescence (PL) spectra of InP/InxGa1-xAs/InAs/InP dot-in-a-well structures grown by MOVPE, with different compositions of the ternary layer. Measurements with atomic force microscopy showed that the largest quantum dot (QD) height is obtained when the InAs QDs are grown on the InxGa1-xAs layer with a mismatch of 1000 ppm, and the height decreases as the mismatch departs from this value. PL spectra of the QDs showed an asymmetric band, which involves transitions between dot energy levels and can be deconvoluted into two peaks. The highest energy PL peak of this band was observed for the sample with the QDs grown on top of the lattice-matched InxGa1-xAs layer and it shifted to lower energies for strained samples as the degree of mismatch increased. Theoretical calculations of the energy levels of the entire structure were used to interpret the obtained PL spectra and determine the possible detection tunability range.  相似文献   

4.
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   

5.
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   

6.
Multiple stacked self-assembled (In1−xMnx)As quantum-dot (QD) arrays were grown on GaAs (100) substrates by using molecular-beam epitaxy with a goal of producing (In1−xMnx)As QDs with a semiconductor phase and a high ferromagnetic transition temperature (Tc). Atomic force microscopy, magnetic force microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray fluorescence measurements showed that crystalline multiple stacked (In0.84Mn0.16)As with symmetric single-domain particle were formed on GaAs substrates. Near-field scanning optical spectroscopy spectra at 10 K for the (In0.84Mn0.16)As multiple stacked QDs showed that the band-edge exciton transitions were observed. The magnetization curve as a function of the magnetic field at 5 and 300 K indicated that the multiple stacked (In0.84Mn0.16)As QDs were ferromagnetic, and the magnetization curve as a function of the temperature showed that the Tc was as high as 400 K. These results provide important information on the optical and magnetic properties for enhancing the Tc of (In1−xMnx)As-based nanostructures.  相似文献   

7.
The effect of strain accumulation in the InAs/In x Ga1−x As quantum dots (QDs) system was studied in this work. We found strain in the In x Ga1−x As layer with accumulation in the QD layer. This effect resulted in a dramatic reduction of growth-mode transition thickness of the QD layer. For InAs/In0.25Ga0.75As QDs, critical thickness is measured to be as low as 1.08 ML. The experimental results in this work highlight the importance of strain accumulation in the design and fabrication of QD-based devices with metamorphic buffer layer involved.  相似文献   

8.
The effect of strain accumulation in the InAs/In x Ga1−x As quantum dots (QDs) system was studied in this work. It was found that strain in the In x Ga1−x As layer accumulation in the QD layer. This effect resulted in a dramatic reduction of growth mode transition thickness of the QD layer. For InAs/In0.25Ga0.75As QDs, critical thickness is measured to be as low as 1.08 ML. The experimental results in this work highlight the importance of strain accumulation in the design and fabrication of QD-based devices with metamorphic buffer layer involved.  相似文献   

9.
We have systematically studied the effect of an InxGa1−xAs insertion layer (IL) on the optical and structural properties of InAs quantum dot (QD) structures. A high density of 9.6×1010 cm−2 of InAs QDs with an In0.3Ga0.7As IL has been achieved on a GaAs (1 0 0) substrate by metal organic chemical vapor deposition. A photoluminescence line width of 25 meV from these QDs has been obtained. We attribute the high density and high uniformity of these QDs to the use of the IL. Our results show that the InGaAs IL is useful for obtaining high-quality InAs QD structures for devices with a 1.3 μm operation.  相似文献   

10.
The effects of the top barrier and the dot density on photoluminescence (PL) of the InAs quantum dots (QDs) sandwiched by the graded InxGa1−xAs barriers grown by metal-organic vapor phase epitaxy (MOVPE) have been studied. Two emission peaks corresponding to the ground state and the 1st excited state transitions of the QD structures have been observed, which matches well to the theoretical calculation. The PL emission linewidth and intensity of the InAs QDs structure are improved by reducing the Indium/Gallium composition variation of the graded InxGa1−xAs top barrier layer of the structure. The QDs’ ground states filling excitation power depends on the crystal quality of the InGaAs barrier layer and the QD density. The extracted thermal activation energy for the QDs’ PL emission is sensitive to the QD size.  相似文献   

11.
Considering the three-dimensional confinement of the electrons and holes and the strong built-in electric field (BEF) in the wurtzite InGaN strained coupled quantum dots (QDs), the positively charged donor bound exciton states and interband optical transitions are investigated theoretically by means of a variational method. Our calculations indicate that the emission wavelengths sensitively depend on the donor position, the strong BEF, and the structure parameters of the QD system.  相似文献   

12.
Reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and double-crystal X-ray curves showed that high-quality InAs quantum dot (QD) arrays inserted into GaAs barriers were embedded in an Al0.3Ga0.7As/GaAs heterostructure. The temperature-dependent photoluminescence (PL) spectra of the InAs/GaAs QDs showed that the exciton peak corresponding interband transition from the ground electronic subband to the ground heavy-hole subband (E1-HH1) was dominantly observed and that the peak position and the full width at half maximum corresponding to the interband transitions of the PL spectrum were dependent on the temperature. The activation energy of the electrons confined in the InAs/GaAs QDs was 115 meV. The electronic subband energy and the energy wave function of the Al0.3Ga0.7As/GaAs heterostructures were calculated by using a self-consistent method. The electronic subband energies in the InAs/GaAs QDs were calculated by using a three-dimensional spatial plane wave method, and the value of the calculated (E1-HH1) transition in the InAs/GaAs QDs was in reasonable agreement with that obtained from the PL measurement.  相似文献   

13.
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   

14.
Based on the effective-mass approximation and variational procedure, ionized donor bound exciton (D+, X) states confined in strained wurtzite (WZ) GaN/AlxGa1-xN cylindrical (disk-like) quantum dots (QDs) with finite-height potential barriers are investigated, with considering the influences of the built-in electric field (BEF), the biaxial strain dependence of material parameters and the applied hydrostatic pressure. The Schrödinger equation via the proper choice of the donor bound exciton trial wave function is solved. The behaviors of the binding energy of (D+, X) and the optical transition associated with (D+, X) are examined at different pressures for different QD sizes and donor positions. In our calculations, the effective masses of electron and hole, dielectric constants, phonon frequencies, energy gaps, and piezoelectric polarizations are taken into account as functions of biaxial strain and hydrostatic pressure. Our results show that the hydrostatic pressure, the QD size and the donor position have a remarkable influence on (D+, X) states. The hydrostatic pressure generally increases the binding energy of (D+, X). However, the binding energy tends to decrease for the QDs with large height and lower Al composition (x<0.3) if the donor is located at z0≤0. The optical transition energy has a blue-shift (red-shift) if the hydrostatic pressure (QD height) increases. For the QDs with small height and low Al composition, the hydrostatic pressure dependence of the optical transition energy is more obvious. Furthermore, the relationship between the radiative decay time and hydrostatic pressure (QD height) is also investigated. It is found that the radiative decay time increases with pressure and the increment tendency is more prominent for the QDs with large height. The radiative decay time increases exponentially reaching microsecond order with increasing QD height. The physical reason has been analyzed in depth.  相似文献   

15.
The bilayer InAs/In0.36Ga0.64As/GaAs(311B) quantum dots (QDs), including one InAs buried quantum dot (BQD) layer and the other InAs surface quantum dot (SQD) layer, have been grown by molecular beam epitaxy (MBE). The optical properties of these three samples have been studied by the piezoreflectance (PzR) spectroscopy. The PzR spectra do not exhibit only the optical transitions originated from the InAs BQDs, but the features originated from the InAs SQDs. After the InAs SQDs have been removed chemically, those optical transitions from InAs SQDs have been demonstrated clearly by investigating the PzR spectra of the residual InAs BQDs in these samples. The great redshift of these interband transitions of InAs SQDs has been well discussed. Due to the suitable InAs SQD sizes and the thickness of In0.36Ga0.64As layer, the interband transition of InAs SQDs has been shifted to ∼1.55 μm at 77 K.  相似文献   

16.
(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   

17.
The photoluminescence (PL), its temperature and power dependences have been studied in InAs quantum dots (QDs) embedded in asymmetric InxGa1?y As/GaAs quantum wells (QWs) with variable InxGa1?x As compositions in the capping layer. Three stages for thermally activated decay of QD PL intensity have been revealed. A set of rate equations for exciton dynamics (relaxation into QWs and QDs, and thermal escape) are solved to analyze the mechanism of PL thermal decay. The variety of PL intensities and peak positions, as well as the activation energies of PL intensity decay in DWELL structures with different compositions of a capping layer are discussed.  相似文献   

18.
The effects of hydrostatic pressure on the exciton ground-state binding energy and the interband emission energy in a GaN/Al x Ga1??? x N quantum dot are investigated. The effects of strain and the internal field due to spontaneous and piezo-electric polarizations are included in the Hamiltonian. Numerical calculations are performed using variational procedure within the framework of single-band effective-mass approximation. The dependence of non-linear optical processes on the dot sizes is brought out in the influence of pressure. Pressure-induced optical properties are obtained using the compact density matrix approach. The effects of hydrostatic pressure on the linear, third-order non-linear optical absorption coefficients and the refractive index changes of the exciton as a function of photon energy are calculated. Our results show that the effects of pressure and the geometrical confinement have great influence on the optical properties of GaN/Al x Ga1??? x N dot.  相似文献   

19.
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   

20.
Considering the strong built-in electric field (BEF) induced by the spontaneous and piezoelectric polarizations and the intrasubband relaxation, we investigate the linear and nonlinear intersubband optical absorptions in InxGa1-xN/AlyGa1-yN strained single quantum wells (QWs) by means of the density matrix formalism. Our numerical results show that the strong BEF is on the order of MV/cm, which can be modulated effectively by the In composition in the QW. This electric field greatly increases the electron energy difference between the ground and the first excited states. The electron wave functions are also significantly localized in the QW due to the BEF. The intersubband optical absorption peak sensitively depends on the compositions of In in the well layer and Al in the barrier layers. The intersubband absorption coefficient can be remarkably modified by the electron concentration and the incident optical intensity. The group-III nitride semiconductor QWs are suitable candidate for infrared photodetectors and near-infrared laser amplifiers.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号