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Extended States in Correlated-Disorder GaAs/AlGaAs Superlattices

  • V. Bellani
  • E. Diez
  • R. Hey
  • G. B Parravicini
  • L. Tarricone
  • F. Domínguez-Adame
Conference paper
Part of the Lecture Notes in Physics book series (LNP, volume 547)

Abstract

We report [1] the first experimental evidence that spatial correlations inhibit localization of states in disordered low-dimensional systems, as previous theoretical calculations suggested [2],[3] in contrast to the earlier belief that all eigenstates are localized. This has been done studying the dc vertical transport and photoluminescence (PL) in GaAs-AlGaAs superlattices (SL’s) with intentional correlated disorder. The spectra are compared to those obtained in ordered and uncorrelated disordered superlattices. To verify this theoretical prevision we grew several n-i-n heterostructures (being i the undoped SL”s) by molecular beam epitaxy. All SL’s have 200 period and Al 0.3 Ga 0.7 As barriers 3.2 nm thick. In the Ordered-SL all the 200 wells are identical with thickness 3.2 nm (hereafter referred to as A wells). In the Random-SL, 58 A wells are replaced by wells of thickness 2.6 nm (hereafter referred to as B wells) and this replacement is done randomly. The so-called Random dimer-SL is identical to the Random-SL with the additional constraint that the B wells appear only in pairs. X-ray diffraction experiments confirm that the dimer constraint intentionally introduced during sample growth is the only difference between the Random and Random Dimer-SL.

We measured [1] the vertical dc resistance of our sample at dark as a function of temperatures. The resistance of the Random Dimer-SL is very similar to the resistance of the Ordered-SL for temperatures below 50K, and the small differences are due to the different miniband-width between the two. On the other hand, Random- SL shows a much higher resistance in this range of temperature. This is due to the presence of extended states in the Random Dimer-SL showing transport properties very similar to a Ordered-SL. According to theoretical studies [3], these extended states in Random Dimer-SL’s are not Bloch-like, as occurs in Ordered-SL’s. PL experiment confirm this interpretation. The PL peak of the Ordered-SL is at the lower energy among the three SL’s. The PL peak of the Random-SL shifts towards higher energies compared with the other two samples. In this SL the intentional disorder introduced by the random distribution of thinner wells B (2.6 nm) localizes the electronic states [3]. The PL peak of the Random Dimer-SL is red-shifted with respect to the PL peak for the Random-SL. This red-shift of the PL peak is due to the formation of a miniband with tunnel process for carriers between the GaAs wells. The position of the electronic levels were calculated with the Kronig-Penney model and calculation show that the Ordered-SL and the Random Dimer-SL exhibit extended electronic states [3]. The experimental PL positions of the three SL’s are in very good agreement with the calculated ones. This is completely consistent with the above interpretation of the transport experiments.

Keywords

Electronic State Spatial Correlation Molecular Beam Epitaxy Extend State Electronic Level 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

References

  1. 1.
    V. Bellani et al., Phys. Rev. Lett., 82, 2159 (1999).CrossRefGoogle Scholar
  2. 2.
    D. H. Dunlap et al., Phys. Rev. Lett. 65, 88 (1990).CrossRefGoogle Scholar
  3. 3.
    E. Diez et al., IEEE J.Quantum Electron. 31, 1919 (1995).CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • V. Bellani
    • 1
  • E. Diez
    • 2
  • R. Hey
    • 3
  • G. B Parravicini
    • 1
  • L. Tarricone
    • 4
  • F. Domínguez-Adame
    • 5
  1. 1.INFM-Dipartimento di Fisica “A. Volta”Università di PaviaPaviaItaly
  2. 2.GISC-Departamento de MatemáticasUniversidad Carlos IIILeganés, MadridSpain
  3. 3.Paul Drude Institut für FestkörperelektronikBerlinGermany
  4. 4.INFM-Dipartimento di FisicaUniversità di ParmaParmaItaly
  5. 5.GISC-Departamento de Física de MaterialesUniversidad ComplutenseMadridSpain

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