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MBE Growth and Characterization of Low Dimensional Systems: Quantum Dots and Two-Dimensional Electron Gas Heterostructures*

V.H. Méndez-García
Instituto de Investigación en Comunicación Optica, Universidad Autónoma de San Luis Potosí,
Av. Karakorum 1470, Lomas 4a Sección, C.P. 78210, San Luis Potosí, S.L.P., México.

In the present work we show recent results on the molecular beam epitaxy (MBE) growth and characterization of AlGaAs/GaAs two-dimensional electron gas (2-DEG) heterostructures, and self-assembled InAs Quantum Dots (QDs).
2-DEG AlGaAs/GaAs heterostructures have very important applications in devices such as, Quantum Hall effect bars used in metrology to obtain the electrical resistance standard, and high electron-mobility transistors (HEMT) used in the wireless communication industry, where high-speed microelectronic circuits are demanded.
On the other hand QD heterostructures are of interests due to the expectation that the optical transition oscillator strength should be condensed into discrete spectral lines owing to the three-dimensional quantum-size effect. Consequently, given sufficient size uniformity and interface quality, quantum dot materials could provide significant performance benefits when incorporated into optoelectronic devices such as semiconductor lasers.
The AlGaAs/GaAs 2-DEG heterostructures were fabricated in a Riber 32P MBE system. The samples were characterized by photoreflectance (PR) and photoluminescence (PL) spectroscopies, and Hall measurements at 77 K. Internal electric fields were detected by the presence of Franz-Keldysh (FK) oscillations in the PR spectra. From a FK analysis we obtained the GaAs and AlGaAs band-gap energies and the built-in electric fields strength in each sample. Results showed that the sample with highest electron mobility exhibited the lowest internal electric field strength.
In the self-assembled growth of  InAs QDs we study the morphological changes after the introduction of Si-impurities at the interface InAs/GaAs. In addition, in situ investigations of the growth have been performed by reflectance difference spectroscopy (RDS) and reflection high-energy electron diffraction (RHEED). By RDS we observe a huge anisotropy induced into the GaAs substrate, presumably related with the intrinsic strain in the Stransky-Krastanov (S-K) growth mode.
* : This work is partially supported by CONACyT

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