Kiatgamolchai, Somchai (2000) Maximum-entropy mobility spectrum of two-dimensional hole gas in strained-Si1-x/Si heterostructures. PhD thesis, University of Warwick.

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Abstract

Magnetotransport properties of modulation-doped p-type Si1-xGex/Si and
Sil_xGex/Sil_yGey heterostructures were studied, in the magnetic field range 0-12 T,
and in the temperature range 0.35-300 K. The experimental data within the classical
regime have been analysed by mobility spectrum analysis, in order to separate the
influences of different parallel conduction paths. A new method of mobility spectrum
analysis has been developed by the author, based on the concept of maximum-entropy,
and this computation has been shown to overcome several drawbacks or limitations
of previous mobility spectrum methods of calculation. The data have also been analysed
by Beck&Anderson's analysis and the multicarrier fitting method for comparison.
Analysis of the magnetic-field-dependent resistivity tensors reveals a two-dimensional
hole gas (2DHG) in the Si/SiGe/Si quantum well, carriers in the boron-doped cap
layer, and an unknown electron-like carrier. The carrier density of the 2DHG can
either remain constant (z = 0.1), increase (x = 0.13), or decrease (x ~ 0.2), with
increasing temperatures. Differences in the temperature dependences are partly attributed
to different growth conditions. A decreasing carrier density with increase in
temperatures may indicate the presence of acceptor-like defect states near the valence
band edge of the SiGe channel. The mobility of the 2DHG between 100-300 K has
the form AT-"Y and 'Y has the bowl shape with the minimum at xf"V0.25-0.3. These
characteristics suggest a possible influence of alloy disorder scattering. The mobilities
and activation energies of the carriers in the boron-doped cap vary between samples
and this is believed to be due to boron-spike near the Si/Si-substrate interface, in
some samples. The source of electron-like carrier is presently unknown.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Mathematical physics, Spectrum analysis , Maximum entropy method
Official Date:	June 2000
Dates:	Date Event June 2000 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Whall, T. E. ; Parker, E. H. C.
Sponsors:	Institute for the Promotion of Teaching Science and Technology (Thailand)
Extent:	xxi, 191 leaves : illustrations
Language:	eng

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