Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generation of high-frequency radiation in semiconductor superlattices
  with suppressed space-charge instabilities   We theoretically investigated the scheme allowing to avoid destructive
space-charge instabilities and to obtain a strong gain at microwave and THz
frequencies in semiconductor superlattice devices. Superlattice is subjected to
a microwave field and a generation is achieved at some odd harmonics of the
pump frequency. Gain arises because of parametric amplification seeded by
harmonic generation. Negative differential conductance (NDC) is not a necessary
condition for the generation. For the mode of operation with NDC, a limited
space-charge accumulation does not sufficiently reduce the gain.

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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
18
The categories of this paper are: econ
26
The categories of this paper are: bayes-an
36
The categories of this paper are: cmp-lg