Microstructural and optical properties of strain compensated InxGa1−xAs/InyAl1−yAs multiple quantum wells

Transmission electron microscopy (TEM) and photocurrent (PC) measurements were carried out to investigate the microstructural and excitonic transitions in In_0.52Ga_0.48As/In_0.55Al_0.45As multiple quantum wells (MQWs). TEM images showed that high-quality 11-period strain-compensated In_0.52Ga_0.48As/In_0.55Al_0.45As MQWs had high-quality heterointerfaces. Based on the TEM results, a possible crystal structure for the In_0.52Ga_0.48As/In_0.55Al_0.45As MQWs is presented, and their strains are compensated. The results for the PC data at 300 K for several applied electric fields showed that several excitonic transitions shifted to longer wavelengths as the applied electric field increased. These results indicate that the strain-compensated In_0.52Ga_0.48As/In_0.55Al_0.45As MQWs hold promise for electroabsorption modulator devices.     

Observation of new critical point in InxAl1−xAs alloy using spectroscopic ellipsometry

Using a spectroscopic ellipsometry, pseudodielectric functions 〈?〉 of In_xAl_1−xAs ternary alloy films (x = 0.43, 0.62, 0.75, and 1.00) from 0.74 to 6.48 eV were determined. Fast in-situ chemical etching to effectively remove surface overlayers using charge-coupled device detector and to avoid the reoxidation of the surface of films prior to the ellipsometric spectrum measurement was performed. At the high energy region, an additional critical point structure which is interpreted as the E′₁ transition from the band structure calculation of the linear augmented Slater-type orbital method was reported.     

In0.53Ga0.47As/In0.52Al0.48As量子阱中的正磁电阻效应

在低温强磁场条件下,对In_0.53Ga_0.47As/In_0.52Al_0.48As量子阱中的二维电子气进行了磁输运测试.在低磁场范围内观察到正磁电阻效应,在高磁场下这一正磁电阻趋于饱和,分析表明这一现象与二维电子气中的电子占据两个子带有关.在考虑了两个子带之间的散射效应后,通过分析低磁场下的正磁电阻,得到了每个子带电子的迁移率,结果表明第二子带电子的迁移率高于第一子带电子的迁移率.进一步分析表明,这主要是由两个子带之间的 关键词： 二维电子气 正磁电阻 子带散射     

Electronic parameters and electronic structures in modulation-doped highly strained InxGa1−xAs/InyAl1−yAs coupled double quantum wells

Electronic parameters of a two-dimensional electron gas (2DEG) in modulation-doped highly strained In_xGa_1−xAs/In_yAl_1−yAs coupled double quantum wells were investigated by performing Shubnikov-de Haas (S-dH), Van der Pauw Hall-effect, and cyclotron resonance measurements. The S-dH measurements and the fast Fourier transformation results for the S-dH at 1.5 K indicated the electron occupation of two subbands in the quantum well. The electron effective masses of the 2DEG were determined from the cyclotron resonance measurements, and satisfied qualitatively the nonparabolicity effects in the quantum wells. The electronic subband structures were calculated by using a self-consistent method.     

In0.53Ga0.47As/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In_0.53Ga_0.47As/In_0.52Al_0.48As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 关键词： 二维电子气 散射时间 自洽计算     

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In_053Ga_047As/In_052Al_0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ΔE₂₁=kω_c(其中k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ΔE₂₁=(2k+1)ω_c/2,填充因子出现奇数. 关键词： 053Ga_047As/In_052Al_048As量子阱')" href="#">In_053Ga_047As/In_052Al_048As量子阱 填充因子 磁输运     

Intersubband transition in symmetric AlxGa1 − xN/GaN double quantum wells with applied electric field

Influence of the applied electric field (AEF) on the intersubband transitions (ISBTs) in symmetric Al_xGa_1 − xN/GaN double quantum wells (DQWs) is investigated by self-consistent calculation. It is found that three- and four-energy-level DQWs can be realized when suitable electric field is applied. When the AEF is 0.93 MV/cm, the 1_odd-2_even ISBT has a comparable absorption coefficient with the 1_even-2_odd ISBT, and the four-energy-level DQWs are realized. The wavelengths of the 1_odd-2_even and 1_even-2_odd ISBTs are located at 1.31 and 1.62 μm, respectively. When the AEF is 1.10 MV/cm, the 1_odd-2_even and 1_odd-2_odd ISBTs have comparable absorption coefficients, and the three-energy-level DQWs are realized. The wavelengths of the 1_odd-2_even and 1_odd-2_odd ISBTs are located at 1.30 and 1.55 μm, respectively. The results suggest promising application to two-color optoelectronic devices operating within optical communication wavelength band, and this study also provides a method for realizing the two-color optoelectronic devices by using the AEF.     

Characterization of aluminium concentration in shallow quantum wells AlxGa1−xAs/GaAs types

We report a reflectance study on series of shallow quantum wells GaAs/Al_xGa_1−xAs types with different aluminium concentration. The observed barrier exciton reflectance line shape depends strongly on the shift in aluminium concentration in the two barriers, with the appropriate choice of the cap layer thickness. This observation was based on the reflectivity line shape analysis of anti-Bragg structures.     

Magnetotransport, optical, and electronic subband properties in AlxGa1−xN/AlN/GaN heterostructures

The Shubnikov-de Haas (S-dH) results at 1.5 K for Al_xGa_1−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 Al_xGa_1−xAs/AlN/GaN heterostructures.     

Simultaneous effects of hydrostatic pressure and applied electric field on the impurity-related self-polarization in GaAs/Ga1−xAlxAs multiple quantum wells

A detailed theoretical study of the combined effects of hydrostatic pressure and in-growth direction applied electric field on the binding energy and self-polarization of a donor impurity in a system of GaAs-(Ga,Al)As coupled square quantum wells is presented. The study is performed in the framework of the effective mass and parabolic band approximations and using a variational procedure. The electron effective mass, the dielectric constant, the barrier height, the well sizes, all them varying with the hydrostatic pressure are taken into account within the study. The results obtained show that the impurity binding energy and its self-polarization bear strong dependencies with the hydrostatic pressure, the strength of the applied electric field, the width of the confining potential barriers, and the impurity position.     

双δ掺杂In0.65Ga0.35As/In0.52Al0.48As赝型高迁移率晶体管材料子带电子特性研究

研究了基于InP基的In_0.65Ga_0.35As/In_0.52Al_0.48As赝型高迁移率晶体管材料中纵向磁电阻的Shubnikov-de Haas(SdH)振荡效应和霍耳效应，通过对纵向磁电阻SdH振荡的快速傅里叶变换分析，获得了各子带电子的浓度，并因此求得了各子带能级相对于费米能级的位置.联立求解Schrdinger方程和Poisson方程，自洽计算了样品的导带形状、载流子浓度分布以及各子带能级和费米能级位置.理论计算和实验结果很好符合.实验和理论计算均表明，势垒层的掺杂电子几乎全部转移到了量子阱中，转移率在95%以上. 关键词： SdH振荡 二维电子气 FFT分析 自洽计算     

Band-edge exciton transitions temperature in multiple stacked self-assembled (In1−xMnx)As quantum dot arrays

Multiple stacked self-assembled (In_1−xMn_x)As quantum-dot (QD) arrays were grown on GaAs (100) substrates by using molecular-beam epitaxy with a goal of producing (In_1−xMn_x)As QDs with a semiconductor phase and a high ferromagnetic transition temperature (T_c). Atomic force microscopy, magnetic force microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray fluorescence measurements showed that crystalline multiple stacked (In_0.84Mn_0.16)As with symmetric single-domain particle were formed on GaAs substrates. Near-field scanning optical spectroscopy spectra at 10 K for the (In_0.84Mn_0.16)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 (In_0.84Mn_0.16)As QDs were ferromagnetic, and the magnetization curve as a function of the temperature showed that the T_c was as high as 400 K. These results provide important information on the optical and magnetic properties for enhancing the T_c of (In_1−xMn_x)As-based nanostructures.     

Study of the optical-electrical characteristics of InxGa1−xN alloy with low in doping

The electronic structures and optical properties of In doped GaN were calculated with different doping concentration, from first-principles using density function theory with the plane-wave ultrasoft pseudopotential method. The influence of In doping on the volume, interactions among atoms, density of states, electron density difference, and optical properties of GaN was analyzed. The results show that the interactions among atoms are reduced, band gap decreases, and absorption spectra have red shift along with the increase of In doping concentration.     

1.3 μm range effectively cylindrical In0.53Ga0.47As/In0.52Al0.48As quantum wires grown on (2 2 1)A InP substrates by molecular beam epitaxy

Vertically coupled quantum wires (QWRs) have been made by alternately stacking nominally 3.6 nm thick In_0.53Ga_0.47As self-organized QWR layers and 1 nm thick In_0.52Al_0.48As barrier layers on (2 2 1)A-oriented InP substrates by molecular beam epitaxy. The surface of In_0.53Ga_0.47As QWR layers was corrugated at an amplitude of 1.1 nm and period of 27 nm, and lateral confinement potential is induced by their thickness modulation. The wavelength of photoluminescence (PL) from the stacked QWRs at 15 K becomes longer from 1220 to 1327 nm with increasing total number of stacked QWR layers, N_SL, from 1 to 9, while PL full-width at half-maximum is reduced from 22 to 8.6 meV. The PL intensity with the polarization parallel to the wire direction, I, is 1.30 times larger than that with the normal polarization, I, when N_SL=1. The PL intensity ratio, I/I, reaches as large as 4 when N_SL=9, indicating successful control of relative strength between vertical confinement and lateral confinement of carriers. The value of I/I obtained for the stacked QWRs with N_SL=9 is the same value as cylindrical QWRs have. The results indicate that effectively cylindrical QWRs with the best uniformity and 1.3 μm range emission were realized by stacking of self-organized QWR layers.     

Optical transitions and carrier dynamics in self-organized InAs quantum dots grown on In0.52Al0.48As/InP(0 0 1)

Optical transitions in self-organized InAs quantum dots (QDs) grown on In_0.52Al_0.48As layer lattice matched to InP(0 0 1) substrate, have been studied by continuous wave (cw) photoluminescence (PL) and time-resolved PL. The dependence of the PL transition on excitation power and photoluminescence excitation measurements clearly shows that the multi-component cw-PL spectrum is related to emission coming from ground and related excited states of QDs with heights varying by monolayer fluctuations. While decay times measured by time-resolved PL are in the nanosecond range for the ground states, shorter decay times related to relaxation of carriers down directly to the ground state are determined for the excited states.     

The variation of electronic properties with the doping concentration of modulation-doped AlxGa1−xAs–GaAs double quantum wells

In this paper we have calculated the sub-band structure and the confinement potential of modulation-doped Ga_1−xAl_xAs–GaAs double quantum wells as a function of the doping concentration. The electronic properties of this structure were determined by self-consistent solutions of the Schrödinger and Poisson equations. To understand the effects of doping concentration on band bending, sub-band energies, and sub-band populations, the doping concentration on one right side of the structure is decreased while holding it constant on the left side. We found that at low doping concentrations on the right side, the effects of the doping concentration are more pronounced on band bending and sub-band populations.     

Characterization of AlxGa1−xAs/GaAs heterostructures for single quantum wells grown by a solid arsenic MOCVD system

This work presents the results of the growth and characterization of Al_xGa_1−xAs/GaAs multilayer structures obtained in a metallic-arsenic-based-MOCVD system. The main goal is to explore the ability of the growth system to grow high quality multilayer structures like quantum wells. The use of metallic arsenic could introduce important differences in the growth process due to the absence of the hydride group V precursor (AsH₃), which manifests in the electrical and optical characteristics of both GaAs and Al_xGa_1−xAs layers. The characterization of these epilayers and structures was performed using low-temperature photoluminescence, Hall effect measurements, X-ray diffraction, Raman spectroscopy, secondary ion mass spectroscopy (SIMS) and Atomic Force Microscopy (AFM).     

Interband transitions and electronic properties of InAs/GaAs quantum dots embedded in AlxGa1−xAs/GaAs modulation-doped heterostructures

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 Al_0.3Ga_0.7As/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 Al_0.3Ga_0.7As/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.     

Optical spectra in the region of exciton resonances in quantum wells and quantum dots of In0.3Ga0.7As/GaAs heterostructures

The transparency, reflection and luminescence spectra of In_0.3Ga_0.7As structures with 8 nm thickness and quantum wells limited by the barrier layer GaAs of a 9 nm (upper layer) and 100 nm (bottom layer) thickness had been studied in the region of photon energy 0.5–1.6 eV. Lines associated with the transitions hh,lh1-e1(1s,2s,3s), hh2,lh2-e2(1s,2s,3s), hh1,lh1-e2(1s) and hh3,lh3-e3(1s) had been revealed in reflection spectra. The shapes of the reflection and transparency lines had been calculated using a single oscillator model of dispersion relations and the Kramers–Kronig integrals. The binding energy of hh,lh1-e1 excitons, the effective mass m_hh^∗ and m_lh^∗ and the damping factor for the optical transitions to QW and QD had been determined. The lifetime of charge carriers on quantum dots varies in the range of 0.04–0.1 ps, while the radiative lifetime of excitons in quantum wells in the considered structure is around 2 ps.     

Dependence of the interband transition and the activation energy on the ZnTe spacer thickness in CdTe/ZnTe double quantum dots

Photoluminescence (PL) measurements were carried out to investigate the interband transition and the activation energy in CdTe/ZnTe double quantum dots (QDs). While the excitonic peaks corresponding to the interband transition from the ground electronic subband to the ground heavy-hole (E₁-HH₁) in the CdTe/ZnTe double QDs shifted to higher energy with decreasing ZnTe spacer thickness from 30 to 10 nm due to transformation from CdTe QDs to Cd_xZn_1−xTe QDs, the peaks of the (E₁-HH₁) transitions shifted to lower energy with decreasing spacer thickness from 10 to 3 nm due to the tunneling effects of the electrons between CdTe double QDs. The decrease in the activation energy with decreasing ZnTe spacer thickness might originate from an increase in the number of defects in the ZnTe spacer. The present results can help improve the understanding of the interband transition and the activation energy in CdTe/ZnTe double QDs.