Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct observation of hole carrier density profiles and their light
  induced manipulation at the surface of Ge   We demonstrate that, by using low-energy positive muon ($\mu^+$) spin
spectroscopy as a local probe technique, the profiles of free charge carriers
can be directly determined in the accumulation/depletion surface regions of p-
or n-type Ge wafers. The detection of free holes is accomplished by measuring
the effect of the interaction of the free carriers with the $\mu^+$ probe spin
on the observable muon spin polarization. By tuning the energy of the
low-energy $\mu^+$ between 1 keV and 20 keV the near-surface region between 10
nm and 160 nm is probed. We find hole carrier depletion and electron
accumulation in all samples with doping concentrations up to the $10^{17}$
cm$^{-3}$ range, which is opposite to the properties of cleaved Ge surfaces. By
illumination with light the hole carrier density in the depletion zone can be
manipulated in a controlled way. Depending on the used light wavelength
$\lambda$ this change can be persistent ($\lambda = 405, 457$ nm) or
non-persistent ($\lambda = 635$ nm) at temperatures $< 270$ K. This difference
is attributed to the different kinetic energies of the photo-electrons.
Photo-electrons generated by red light do not have sufficient energy to
overcome a potential barrier at the surface to be trapped in empty surface
acceptor states. Compared to standard macroscopic transport measurements our
contact-less local probe technique offers the possibility of measuring carrier
depth profiles and manipulation directly. Our approach may provide important
microscopic information on a nanometer scale in semiconductor device studies.

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The categories of this paper are: acc-phys
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The categories of this paper are: comp-gas
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The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: plasm-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-th
34
The categories of this paper are: chem-ph