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.     

Thermal quenching of extrinsic photoluminescence of GaAs-Ga1-x Al x As single quantum well

Summary The temperature dependence of the emission intensity due to conduction band-to-neutral acceptor recombination (e-A⁰) is investigated in a GaAs/Ga_0.7Al_0.3As single quantum well. It is shown that the thermal quenching of the (e-A⁰) emission peak is not monotonous with temperature. The increase of the (e-A⁰) emission intensity up to about 30 K is interpreted as a consequence of the ionization of shallow donors, while the decrease in emission intensity at higher temperature is due to ionization of neutral acceptors.     

Large negative magnetoresistance introduced by line dislocations in a modulation doped Ga0.25In0.75As/InP quantum well

A large negative magnetoresistance at low magnetic fields of a high mobility two dimensional electron gas in a modulation-doped Ga_0.25In_0.75As/InP quantum well containing dislocations is reported. The effect is attributed to electrons on open orbits caused by scattering against the potential created by line dislocations formed in the Ga_0.25In_0.75As layer when the critical thickness for growth on InP was exceeded. By comparing the magnetoresistance for the structures containing dislocations with those without, but with etched trenches with a similar distribution as the line dislocations, we conclude that the dislocations introduce a strong potential in the two dimensional electron gas.     

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).     

Two-dimensional probe absorption spectrum in a semiconductor quantum well

We investigate the two-dimensional (2D) probe absorption spectrum in a semiconductor quantum well driven by two orthogonal standing-wave lasers. It is found that, due to the position-dependent quantum interference, the 2D spatial distribution of probe absorption spectrum can be easily controlled via adjusting the system parameters. Thus, our scheme shows the underlying probability for the applications in solid-state optic communication and transmission.     

Investigation of weak damage in Al0.25Ga0.75As/GaAs by using RBS/C and Raman spectroscopy

The weak damage induced by 0.8 MeV Si ion implantation in the Al_0.25Ga_0.75As films epitaxially grown on GaAs substrates was studied by using Rutherford backscattering spectrometry/channeling (RBS/C) and Raman spectroscopy. RBS/C spectra measured from the implanted samples showed rather low damage level induced by the ion implantation with ion dose from 1×10¹⁴ to 5×10¹⁵ cm⁻². The Raman spectra were measured on these samples. Two kinds of phonon modes, GaAs-like and AlAs-like, are observed, which indicate the existence of multiple phonon vibrational modes in the epitaxial Al_0.25Ga_0.75As films on the GaAs substrate. Compared with the unimplanted sample, the Raman photon peaks for the implanted sample shift gradually to lower energy with the increase of the implantation dose. The strains induced in the implanted layer were also evaluated from the Raman spectra. The result from high resolution double crystal X-ray diffractometry (HRXRD) also verified the evolution of the strains in the implanted layers.     

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.     

Magneto-optical study of nonmagnetic quantum dots coupled to a magnetic semiconductor quantum well

We have investigated a series of double-layer structures consisting of a layer of self-assembled non-magnetic CdSe quantum dots (QDs) separated by a thin ZnSe barrier from a ZnCdMnSe diluted magnetic semiconductor (DMSs) quantum well (QW). In the series, the thickness of the ZnSe barrier ranged between 12 and 40 nm. We observe two clearly defined photoluminescence (PL) peaks in all samples, corresponding to the CdSe QDs and the ZnCdMnSe QW, respectively. The PL intensity of the QW peak is observed to decrease systematically relative to the QD peak as the thickness of the ZnSe barrier decreases, indicating a corresponding increase in carrier tunneling from the QW to the QDs. Furthermore, polarization-selective PL measurements reveal that the degree of polarization of the PL emitted by the CdSe QDs increases with decreasing thickness of the ZnSe barriers. The observed behavior is discussed in terms of anti-parallel spin interaction between carriers localized in the non-magnetic QDs and in the magnetic QWs.     

A KKR-CPA study of the electronic states in Ti0.75Al0.25N

The partial densities of states (DOS) and the X-ray emission spectra of the random alloy Ti_0.75Al_0.25N were calculated using the KKR-CPA method. While the Ti and N atoms behave much the same as in TiN, the Al bonding is found to be different from both A1N and metallic Al.     

Two-photon absorption processes in GaAs/Al x Ga1−x As quantum wells

Summary The two-photon absorption spectra of GaAs/AlGaAs multiple quantum well and superlattice structures have been experimentally investigated by means of the nonlinear luminescence technique in different polarization configurations. A strong excitonic effect overlapping the interband two-photon spectrum has been found and the selection rules for the excitonic transitions have shown to greatly change for different polarizations. The comparison of linear and nonlinear absorption measurements provides important information on the excited states of excitons in multiple quantum wells. Work partially supported by M.P.I.     

Impurity optical absorption in parabolic quantum well

Optical absorption in GaAs parabolic quantum well in the presence of hydrogenic impurity is considered. The absorption coefficient associated with the transitions between the upper valence subband and donor ground state is calculated. The impurity ground state wave function and energy are obtained using the variational method. Dependence of the absorption spectra on impurity position in quantum well was investigated. It is shown, that along with quantum well width decrease the absorption threshold shifts to higher frequencies. Results obtained within frames of parabolic approximation are compared with results for rectangular infinite-barrier quantum well case. The acceptor state → conduction band transitions considered as well.     

Optical absorption coefficients in asymmetric quantum well

The optical absorption coefficients considering electron-phonon interaction in asymmetrical quantum wells are theoretically studied. The result shows that the optical absorption coefficients depend strongly on the parameters of quantum well. Interestingly, the theoretical values of the optical absorption coefficients obviously increase with considering the electron-phonon interaction.     

Two-electron absorption in a biased quantum well

Linear light absorption of 2D electrons confined within a biased quantum well is studied theoretically. We demonstrate that for light polarization perpendicular to the 2D plane, in addition to conventional absorption peak at frequency ω≈Δ, where Δ is the intersubband energy distance, there exists a peak around a double frequency ω≈2Δ. This additional peak is entirely due to electron–electron interactions, and corresponds to excitation of two electrons by one photon. The magnitude of two-electron absorption is proportional to U², where U is the applied bias.     

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.     

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.     

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.