Investigation of barrier tunneling characteristics of symmetrical double quantum well in In0.25Ga0.75As/GaAs/In0.25Ga0.75As heterostructure

The optical and electrophysical properties of the GaAs/In_0.25Ga_0.75As heterostructure with a symmetric double quantum well have been investigated. The influence of tunneling electrons and holes through an internal barrier of the quantum well on the shift and splitting of the quantum levels is analyzed. The theoretical estimates are compared with the results of the photoluminescence and photoconductivity measurements. The Hall measurements indicate that the barrier strongly affects the mobility of charge carriers.     

压电调制反射光谱研究GaAs/Al0.29Ga0.71 As单量子阱

报道了压电调制反射测量系统的建立,应用该系统获得了势阱宽度分别为5nm和25nm的两个GaAs/Al0.29Ga0.71As单量子阱的压电调制反射谱.从图谱中可以看出,在室温下能够较容易地分辨出和轻、重空穴相关联的子带跃迁.在阱宽25nm的样品中还观察到了自旋-轨道跃迁.利用有效质量理论近似计算,对量子阱样品的图谱结构进行了指认,发现实验值和计算值能够较好地符合.     

Effect of a Coulomb well in (In,Ga)As/GaAs quantum wells

Magnetooptical investigation of exciton transitions in high-quality quantum wells of an (In, Ga)As/GaAs heterosystem has been carried out. Investigation of transmission of free-hanging samples detached from the substrate in the magnetic fields of up to 12 T revealed a rich fine structure associated with various heavy-hole and light-hole exciton transitions. In particular, transitions from the excited states of light holes localized in a Coulomb potential produced by an electron along the heterojunction axis (a Coulomb well) have been detected. Taking into account consistently stresses, formation of Landau levels, the binding energies of excitons (diamagnetic excitons), and the effect of a Coulomb well, we have succeeded to describe the experimental results with the use of a self-consistent variational procedure. As a result, new features in the structure of optical transitions have been explained and the effective masses of electrons and holes of excitons formed by both heavy and light holes have been determined with a high accuracy.     

Recombination in tensile-strained In0.3Ga0.7As quantum well on InP

Photoluminescence (PL) measurements under different excitation powers were carried out at low temperature on tensile-strained In_0.3Ga_0.7As single wells of 6 nm with InGaAs barriers lattice matched to InP substrate. PL measurements taken at 2 K show a main emission band at 0.762 eV probably originating from a type-II transition. The insertion of an ultrathin InAs layer at In_0.3Ga_0.7As on In_0.53Ga_0.47As interface reveals an additional feature at 0.711 eV as well as an excited-state luminescence emission at high pump powers. The InAs insertion improves heterointerface quality, which was confirmed by an increase in PL intensity.     

Energy sublevels in an Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As quantum wire

We report the successful fabrication of a V-grooveAl_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As quantum wire system and the temperature-dependent photoluminescence (PL) measurement. The PL spectra are dominated by four features at 681, 642, 635 and 621 nm attributed to the luminescences from quantum wire, top, vertical and side-wall well regions by micro-PL measurements. By the calculations of the energy structure, discrete states (localized sublevels) in the quantum wire region and continuum states (extended along the side-wall and vertical quantum wells) in side-wall and vertical quantum wells have been obtained in both the conduction and valence bands. The calculated excitation energies explain very well the peak positions and their temperature dependence in the photoluminescence measurements.     

Design of strain-compensated In x Ga1-x As/In y Al1-y As quantum cascade laser structures towards the shorter wavelengths

We design the In _x Ga_1-x As/In_yAl_1-yAs quantum cascade laser (QCL) structures, based on the four-quantum well active region with vertical transition with strain compensation towards the shorter wavelengths, operating at λ ~2.93–6.6μm. Considering the objective function related to the optical gain, i.e., ${z_{43}^2 (1-\tau_3 /\tau_{43})\tau_4}$ , and the escape energy related to the carrier leakage to continuum, the design of QCLs is carried out in double infinite feedback loops. Each barrier/well layer in the active region is optimized towards the lasing wavelength as short as possible under a properly designed injector. For efficient short wavelength emission, the larger conduction band discontinuity (ΔE _c ) is achieved by changing the indium mole fractions of strain-compensated In _x Ga_1-x As/In_yAl_1-y As layers. The experimentally verified injectors are properly modified for the stronger coupling between the wavefunctions of the ground state in injector and the upper state in active region. Thus the use of strain-compensated In_0.72Ga_0.28As/In_0.3Al_0.7As structure (i.e., ΔE _c = 857 meV) leads to the shortest wavelength up to λ ~2.93μm with τ ₄₃ = 2.13 ps, τ ₄ = 0.87 ps, τ ₃ = 1.43 ps and z ₄₃ = 1.03 nm under an electric field of 96 kV/cm.     

Electron-density-dependent optical spectra of a remotely-doped GaAs/Al0.33Ga0.67As single quantum well

We have measured electroreflectance (ER) and photoluminescence (PL) spectra of a high-quality remotely-doped GaAs/Al_0.33Ga_0.67As quantum well (QW) as a function of electron density. Both techniques show the transition from the electron Fermi energy to the ground hole subband, although it is enhanced in ER due to its strong blue shift with electron density. The negligible Stokes shift of the transition demonstrates that the holes involved in the recombination are not strongly localised, consistent with the absence of a distinct peak due to the Fermi edge singularity. The ER spectra show in addition several transitions from the Fermi energy to excited hole subbands. Transitions involving the second and third electron subbands shift to lower energy with electron density due to both the Stark shift induced by the charge in the QW and bandgap renormalisation, which we compare to calculations.     

Weak localization in Al0.25Ga0.75As/In0.2Ga0.8As/GaAs wires

The phase coherence length L_Ø, its temperature dependence and the spin-orbit scattering length L_SO in Al_0.25Ga_0.75As/In_0.2Ga_0.8As/GaAs wires fabricated by electron-beam lithography and CH₄/H₂ Reactive Ion Etching (RIE), were extracted by fitting a 1-dimensional weak localization theory to two-terminal measurements in the temperature range between 2 K and 50 K. The scattering mechanism was found to be Nyquist (electron-electron collisions with small energy transfer).     

Electronic transport in strained p-modulation Be-doped Ga0.8In0.2As/GaAs single quantum well

We report on the electronic transport properties of p-modulation Be-doped Ga_0.8In_0.2As/GaAs single quantum well. The experiments included the spectral photoluminescence between 8 and 300?K, and Hall effect measurements at temperatures between 14 and 300?K. The effect of strain which induces splitting of the valence band as light and heavy hole bands on transport is discussed. The calculated band alignment of the GaInAs sample using model-solid theory including strain effects indicates large conduction band discontinuities and a much smaller valance band discontinuity in GaInAs. The effect of the conduction and valance band discontinuity on the electronic transport properties is also discussed.     

Spectrum analysis of interband optical transmissions and quantitative model of eigen-energies and absorptions in In0.53Ga0.47As/In0.52Al0.48As multi-quantum well structures

Interband transmission spectra were measured for three In_0.53Ga_0.47As/In_0.52Al_10.48As multi-quantum well specimens having different carrier concentrations by modulation-doping. Spectral shapes of transmissions were clear steplike structures but exciton peaks of first order transitions were masked with the carrier concentrations. The spectral shapes changed hardly between 100 and 310 K. Using our parameters of quantum wells, calculated eigen-energies for three specimens agreed with experiments and absorption coefficients reproduced experimental transmission spectra at any temperature.     

Energy band modulation of GaAs/Al0.26Ga0.74As quantum well in 3D self-assembled nanomembranes

In this study, we investigate the modulation of energy band in 3D self-assembled nanomembranes containing GaAs/Al_0.26Ga_0.74As quantum wells (QWs). Photoluminescence (PL) characterizations demonstrate that the self-assembled structures have different optical transition properties and the modulation of the energy band is thus realized. Detailed spectral analyses disclose that the small strain change in structures with different curvatures cannot cause remarkable change in energy bands in Al_0.26Ga_0.74As layer. On the other hand, the optical transitions of GaAs QW layer is influenced by the strain evolution in term of light emission intensity. We also find the first order Stark effect in rolled-up nanomembrane with diameter of 150 μm, which is closely connected with the coupling effect between the deformation potential and the piezoelectric potential. Our work may pave a way for the fabrication of high performance rolled-QW infrared photo-detectors.     

Coherent oscillations of holes in GaAs0.86P0.14/Al0.7Ga0.3As surface quantum well

We show that in a GaAs_0.86P_0.14/Al_0.7Ga_0.3As near-surface quantum well, there is coherent oscillation of holes observed in time-resolved reflectivity signal when the top barrier of the quantum well is sufficiently thin. The quantum well states interact with the surface states under the influence of the surface electric field. The time period of the observed oscillation is 120±10 fs.     

两个子带占据的In0.53Ga0.47As/In0.52Al0.48As量子阱中填充因子的变化规律

研究了低温(1.5K)和强磁场(0-13T)条件下,InP基In0.53Ga0.47As/In0.52Al0.48As量子阱中电子占据两个子带时填充因子随磁场的变化规律.结果表明,在电子自旋分裂能远小于朗道能级展宽的情况下,如果两个子带分裂能是朗道分裂能的整数倍时,即⊿E21=κ*ωc(其中κ为整数),填充因子为偶数;当两个子带分裂能为朗道分裂能的半奇数倍时,即⊿E21=(2κ 1*ω/2,填充因子出现奇数.     

In0.53 Ga0.47As/In0.52Al0.48As量子阱中双子带占据的二维电子气的输运特性

研究了不同沟道厚度的In0.53 Ga0.47As/In0.52Al0.48As量子阱中双子带占据的二维电子气的输运特性.在考虑了两个子带电子之间的磁致子带间散射效应后,通过分析Shubnikov-de Haas振荡一阶微分的快速傅里叶变换结果,获得了每个子带电子的浓度、输运散射时间、量子散射时间以及子带之间的散射时间.结果表明,对于所研究的样品,第一子带电子受到的小角散射更强,这与第一子带电子受到了更强的电离杂质散射有关.     

Influence of quantum dot density on excitonic transport and recombination in CdZnTe/ZnTe QD structures

We report on dynamics of excitons in Cd_xZn_1−xTe/ZnTe quantum dots (QDs) and present information of excitonic transport and recombination. Due to different growth methods, samples with different QD's densities were obtained. Time-resolved measurements reveal three decay mechanisms: (i) radiative recombination of excitons in the individual QDs; (ii) thermally activated escape of excitons and (iii) escape due to tunneling (hopping). In the high QD-density samples the hopping (r_HB=2700 ns⁻¹) is two orders of magnitude more efficient than in the low QD-density samples (r_HB=33 ns⁻¹). Radiative recombination rates are similar in both types of samples, r_R=1-1.3 ns⁻¹. Due to the good radiative to nonradiative recombination ratio, the low-density QDs can be a potential source of entangled photon pairs.