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Pseudomorphic In0.2Ga0.8As/GaAs quantum wells (QWs) were grown by molecular beam epitaxy on GaAs substrates oriented along s11nd directions, with n=1,2,3,4. The optical and structural properties of the heterostructures were studied by photoluminescence (PL), photoreflectance (PR) spectroscopy, and atomic force microscopy measurements. The energy transitions in the QWs have two contributions, a blueshift due to the compressive strain, and a redshift due to the quantum confined Stark effect produced by the piezoelectric field present in the QWs. A variational approach was employed to calculate the QWs ground energy transitions employing an ideal potential well with sharp interfaces. The theoretical energy transitions were fitted to the PL peaks energy to obtain the electric fields in the InGaAs QWs. The obtained electric fields show discrepancies with theoretical piezoelectric fields calculated from the strain present in the QWs. In order to overcome these discrepancies, we propose to include interdiffusion effects of In at the well interfaces. The matrix transfer method was implemented to numerically solve the Schrödinger equation taking into account In interdiffusion effects by including an asymmetric potential well with a profile depending on the details of the In incorporation. With interdiffusion effects included in the energy level calculations, and assuming the expected piezoelectric fields, the theoretical results reproduce very well the experimental values of PL and PR. [ABSTRACT FROM AUTHOR]

Quantum well (QW) structures of Al x Ga1- x As/GaAs with x = 0.3 were characterized by photoluminescence spectroscopy (PL) with circularly polarized excitation at a temperature of 1.6 K. The samples contained three QWs with thickness of 7, 5, and 3 nm grown by molecular beam epitaxy (MBE) on a 500 nm thick buffer layer. Four samples with identical geometry but different surface treatments (in-situ etching the GaAs buffer with Cl2 at different temperatures, and air-exposed buffer, respectively) were compared. The degree of circular polarization of the PL and its decrease in a magnetic field applied perpendicularly to the direction of propagation of light (Hanle effect) allows the determination of the interband lifetime τ and the spin lifetime τ s of the electrons. These lifetimes were different in the different QWs and strongly depend on the growth procedure. [ABSTRACT FROM AUTHOR]

We have studied the GaAs growth on (631) oriented substrates by molecular beam epitaxy (MBE). Different samples were prepared by varying the growth temperature and the III/V equivalent pressure ratio. We observed by atomic force microscopy a high density of hilly like features elongated towards the [-5,9,3] direction formed during the MBE growth. The growth temperature dependence of the hillock length and width follows an Arrhenius-type behavior with activation energies of 1.4 and 0.5 eV, respectively. The hillock formation is discussed in terms of adatom diffusion anisotropy and diffusion barriers. Employing photoreflectance spectroscopy we found a splitting of the GaAs band gap energy transition that increases with the hillock density. [ABSTRACT FROM AUTHOR]

The optical properties of MBE-grown quantum Hall effect devices have been studied by photoreflectance spectroscopy (PR) at different temperatures. The room temperature PR spectra show two typical signals around 1.42 and 1.85 eV attributed to the energy band edges of GaAs and AlGaAs, respectively. Between the former band edge transitions broad oscillations (BO) are observed. 15 K PR spectra from samples and photoluminescence spectroscopy reveal that a component of the BO is originated from the surface quantum well (SQW) created by the AlGaAs–GaAs–vacuum discontinuity. This signal experience a blue shift when the GaAs is gradually etched-off in good agreement with the PR spectra behavior from SQWs previously reported. Besides, PR measurements were performed at low temperatures. In this process, the near-surface band bending of the structures is virtually flattened during the cooling procedure. We observed a signal whose intensity decreased as the temperature is lowered. Therefore, the former results suggest that BO consist in two superimposed signals coming from the SQW and the electric field cap region. [Copyright &y& Elsevier]

Abstract: A series of quantum well (QW) structures of Al0.3Ga0.7As/GaAs were characterized by photoluminescence spectroscopy with circularly polarized excitation at 1.6 K. The samples were grown by molecular beam epitaxy on a 500 nm thick GaAs buffer layer and contained three QW structures with thicknesses of 7, 5, and 3 nm, respectively. Four samples were prepared with different processing of the GaAs buffer layer surface (i: continuous growth, ii: in situ etching the GaAs buffer with Cl2 at 70 °C, iii: at 200 °C, respectively and iv: air-exposed buffer). The influence of buffer surface preparation on sample characteristics was analyzed. Using the Hanle effect the interband lifetime and the spin lifetime of the electrons were determined. A negative spin polarization was observed if the photon energy of the exciting light exceeds the difference between the spin–orbit band and the conduction band. This inverse circular polarization could be related to the quality of the sample. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we have studied the dependence of the size and luminescence of self-assembled InAs quantum dots (SAQDs) on the growth conditions. The SAQDs were grown on GaAs (100) substrates by molecular beam epitaxy (MBE). Their structural and optical properties were studied by atomic force microscopy (AFM), and photoluminescence spectroscopy (PL). The growth of the InAs SAQDs was in situ monitored by reflection high-energy electron diffraction (RHEED). The shape and size of the InAs SAQDs were significantly affected by the growth temperature and the arsenic over-pressure. We observe a decrease of the SAQDS density and an increase in their height by increasing the growth temperature, and/or decreasing the arsenic over-pressure. This is accompanied by a remarkable red-shift of the PL emission energy from 1.3 to . [Copyright &y& Elsevier]

Abstract: InAs layers with thickness of monolayer (-layers) were grown by MBE embedded in GaAs barriers in the direction [100]. Photoluminescence (PL) spectroscopy was employed to study the electronic transitions in the -layers. By secondary-ion mass spectroscopy (SIMS) we checked out the possible In segregation. The samples consist of five InAs -layers embedded in between 60nm-thick GaAs barriers, such that the electron wave functions do not overlap each other, as we verified with a model of a square quantum well (SQW), which help us to calculate also the well width. [Copyright &y& Elsevier]