Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A study of the optical and polarisation properties of InGaN/GaN multiple
  quantum wells grown on a-plane and m-plane GaN substrates   In this paper we report on a comparative study of the low temperature
emission and polarisation properties of InGaN/GaN quantum wells (QWs) grown on
nonpolar a-plane and m-plane free-standing bulk GaN substrates where the In
content varied from 0.14 to 0.28 in the m-plane series and 0.08 to 0.21 for the
a-plane series. The low temperature photoluminescence spectra from both sets of
samples are very broad with full width at half-maximum height increasing from
81 to 330 meV as the In fraction increases. Comparative photoluminescence
excitation spectroscopy indicates that the recombination mainly involves
strongly localised carriers. At a temperature of 10 K the degree of linear
polarisation of the a-plane samples is much smaller than of the m-plane
counterparts and also varies across the spectrum. From polarisation-resolved
photoluminescence excitation spectroscopy we measured the energy splitting
between the lowest valence sub-band states to lie in the range of 23-54 meV for
both a-and m-plane samples in which we could observe distinct exciton features
in the polarised photoluminescence excitation spectroscopy. Thus, the thermal
occupation of a higher valence subband cannot be responsible for the reduction
of the degree of linear polarisation. Time-resolved spectroscopy indicates that
in a-plane samples there is an extra emission component which at least partly
responsible for the reduction in the degree of linear polarisation.

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The categories of this paper are: acc-phys
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The categories of this paper are: astro-ph
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The categories of this paper are: cs
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The categories of this paper are: atom-ph
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The categories of this paper are: q-bio
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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: adap-org
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The categories of this paper are: econ
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: plasm-ph