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SUMMARY:2D Transport Measurements in Undoped Electron Systems - Ben Ramsay
 \, Cavendish Laboratory\, University of Cambridge\, UK
DTSTART:20180214T140000Z
DTEND:20180214T150000Z
UID:TALK101395@talks.cam.ac.uk
CONTACT:Dr Kaveh Delfanazari
DESCRIPTION:The MBE growth of ultra-high-quality GaAs/AlGaAs epilayer stru
 ctures has enabled the discovery of many novel physical phenomena - for ex
 ample\, the fractional quantum Hall effect (FQHE) in two- dimensional elec
 tron systems (2DESs)[1]. In order to attain the highest electron mobilitie
 s\, it is necessary to understand and limit the dominant sources of disord
 er during the wafer growth. These include both intentional (i.e. doping) a
 nd unintentional charged impurities\, interface roughness\, and surface de
 fect states\, all of which cause electron scattering. \n     The electron 
 mobility in a modulation-doped 2DES is dominated by doping impurities. By 
 contrast\, the electron mobility in an undoped 2DES is dominated by uninte
 ntional background impurities and interface roughness. By measurement and 
 numerical modelling of the mobility versus density characteristics of an u
 ndoped wafer\, it is possible to determine the concentration of background
  impurities and the characteristic length and height scales of the interfa
 ce roughness[2\,3]. \n     In this talk I will present experimental data o
 f electron mobility in an undoped heterostructure at 0\, 45 and 90 to the 
 major flat of the wafer\, and how numerical modelling of the electron mobi
 lity can be used to explain the dependence of mobility on angle to the maj
 or flat. I will also discuss how assumptions about the shape of the electr
 on wave function[4] in the potential well formed by the heterostructure ma
 y limit the accuracy of the mobility modelling\, and how the model can be 
 extended using numerical solutions for the wave function.  \n\nReference:\
 n[1] D. C. Tsui\, H. L. Stormer\, and A. C. Gossard\, “ Two- dimensional
  magnetotransport in the extreme quantum limit\,” Phys. Rev. Lett.\, vol
 . 48\, pp. 1559–1562\, may 1982.\n[2] A. F. Croxall\, B. Zheng\, F. Sfig
 akis\, K. Das Gupta\, I. Farrer\, C. A. Nicoll\, H. E. Beere\, and D. A. R
 itchie\, “Demonstration and characterization of an ambipolar high mobili
 ty transistor in an undoped GaAs/AlGaAs quantum well\,” Appl. Phys. Lett
 .\, vol. 102\, no. 8\, p. 082105\, 2013.\n[3] W. Y. Mak\, K. Das Gupta\, H
 . E. Beere\, I. Farrer\, F. Sfigakis\, and D. A. Ritchie\, “Distinguishi
 ng impurity concentrations in GaAs and AlGaAs using very shallow undoped h
 eterostructures\,” Appl. Phys. Lett.\, vol. 97\, no. 24\, p. 242107\, 20
 10.\n[4] F. F. Fang and W. E. Howard\, “Negative field-effect mobility o
 n (100) Si surfaces\,” Phys. Rev. Lett.\, vol. 16\, pp. 797–799\, may 
 1966.\n
LOCATION:Mott Seminar Room (Mott Building Room 531)\, Cavendish Laboratory
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