Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spin-dependent direct gap emission in tensile-strained Ge films on Si
  substrates   The circular polarization of direct gap emission of Ge is studied in
optically-excited tensile-strained Ge-on-Si heterostructures as a function of
doping and temperature. Owing to the spin-dependent optical selection rules,
the radiative recombinations involving strain-split light (cG-LH) and heavy
hole (cG-HH) bands are unambiguously resolved. The fundamental cG-LH transition
is found to have a low temperature circular polarization degree of about 85%
despite an off-resonance excitation of more than 300 meV. By photoluminescence
(PL) measurements and tight binding calculations we show that this
exceptionally high value is due to the peculiar energy dependence of the
optically-induced electron spin population. Finally, our observation of the
direct gap doublet clarifies that the light hole contribution, previously
considered to be negligible, can dominate the room temperature PL even at low
tensile strain values of about 0.2%.

30
The categories of this paper are: q-alg
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
23
The categories of this paper are: solv-int