A study of photomodulated reflectance on staircase-like, n-doped GaAs/AlxGa1−xAs quantum well structures

Nanoscale Research Letters (Impact Factor: 2.78). 11/2012; 7(1):622. DOI: 10.1186/1556-276X-7-622
Source: PubMed


In this study, photomodulated reflectance (PR) technique was employed on two different quantum well infrared photodetector (QWIP) structures, which consist of n-doped GaAs quantum wells (QWs) between undoped AlxGa1−xAs barriers with three different x compositions. Therefore, the barrier profile is in the form of a staircase-like barrier. The main difference between the two structures is the doping profile and the doping concentration of the QWs. PR spectra were taken at room temperature using a He-Ne laser as a modulation source and a broadband tungsten halogen lamp as a probe light. The PR spectra were analyzed using Aspnes’ third derivative functional form.
Since the barriers are staircase-like, the structure has different ground state energies; therefore, several optical transitions take place in the spectrum which cannot be resolved in a conventional photoluminescence technique at room temperature. To analyze the experimental results, all energy levels in the conduction and in the valance band were calculated using transfer matrix technique, taking into account the effective mass and the parabolic band approximations. A comparison of the PR results with the calculated optical transition energies showed an excellent agreement. Several optical transition energies of the QWIP structures were resolved from PR measurements. It is concluded that PR spectroscopy is a very useful experimental tool to characterize complicated structures with a high accuracy at room temperature.

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Available from: Omer Donmez, May 06, 2014
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    ABSTRACT: The electron Land\'e $g$ factor $({g}^{*})$ is investigated both experimentally and theoretically in a series of ${\mathrm{GaBi}}_{x}{\mathrm{As}}_{1$-${}x}/\mathrm{GaAs}$ strained epitaxial layers, for bismuth compositions up to $x=3.8%$. We measure ${g}^{*}$ via time-resolved photoluminescence spectroscopy, which we use to analyze the spin quantum beats in the polarization of the photoluminescence in the presence of an externally applied magnetic field. The experimental measurements are compared directly to atomistic tight-binding calculations on large supercells, which allows us to explicitly account for alloy disorder effects. We demonstrate that the magnitude of ${g}^{*}$ increases strongly with increasing Bi composition $x$ and, based on the agreement between the theoretical calculations and experimental measurements, elucidate the underlying causes of the observed variation of ${g}^{*}$. By performing measurements in which the orientation of the applied magnetic field is changed, we further demonstrate that ${g}^{*}$ is strongly anisotropic. We quantify the observed variation of ${g}^{*}$ with $x$, and its anisotropy, in terms of a combination of epitaxial strain and Bi-induced hybridization of valence states due to alloy disorder, which strongly perturbs the electronic structure.
    No preview · Article · Nov 2014 · Physical Review B