  We have studied experimentally and theoretically the optical orientation and
spin-dependent Shockley-Read-Hall recombination in a semiconductor in a
magnetic field at an arbitrary angle between the field and circularly polarized
exciting beam. The experiments are performed at room temperature in GaAsN
alloys where deep paramagnetic centers are responsible for the spin-dependent
recombination. The observed magnetic-field dependences of the circular
polarization r(B) and intensity J(B) of photoluminescence can be approximately
described as a superposition of two Lorentzian contours, normal and inverted,
with their half-widths differing by an order of magnitude. The normal (narrow)
Lorentzian contour is associated with depolarization of the transverse (to the
field) component of spin polarization of the localized electrons, whereas the
inverted (broad) Lorentzian is due to suppression of the hyperfine interaction
of the localized electron with the defect nucleus. The ratio between the height
of one Lorentzian and depth of the other is governed by the field tilt angle.
In contrast to the hyperfine interaction of a shallow-donor-bound electron with
a large number of nuclei of the crystal lattice, in the optical orientation of
the electron-nuclear system under study no additional narrow peak appears in
the oblique field. This result demonstrates that in the GaAsN alloys the
hyperfine interaction of the localized electron with the single nucleus of the
paramagnetic center remains strong even at room temperature. For a theoretical
description of the experiment, we have extended the theory of spin-dependent
recombination via deep paramagnetic centers with the nuclear angular momentum I
= 1/2 developed previously for the particular case of the longitudinal field.
The calculated curves r(B), J(B) agree with the approximate description of the
experimental dependences as a sum of two Lorentzians.
