Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Study of two-subband population in Fe-doped AlxGa1-xN/GaN
  heterostructures by persistent photoconductivity effect   The electronic properties of Fe-doped Al0.31Ga0.69N/GaN heterostructures have
been studied by Shubnikov-de Haas measurement. Two subbands of the
two-dimensional electron gas in the hetero-interface were populated. After the
low temperature illumination, the electron density increases from 11.99 x 1012
cm-2 to 13.40 x 1012 cm-2 for the first subband and from 0.66 x 1012 cm-2 to
0.94 x 1012 cm-2 for the second subband. The persistent photoconductivity
effect (~13% increase) is mostly attributed to the Fe-related deep-donor level
in GaN layer. The second subband starts to populate when the first subband is
filled at a density n1 = 9.40 x 1012 cm-2. We calculate the energy separation
between the first and second subbands to be 105 meV.

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The categories of this paper are: funct-an
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The categories of this paper are: atom-ph
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The categories of this paper are: adap-org
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The categories of this paper are: q-fin
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: cmp-lg
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The categories of this paper are: astro-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess