  We explore various aspects of magneto-conductance oscillations in
semiconductor nanowires, developing quantum transport models based on the
non-equilibrium Green's function formalism. In the clean case, Aharonov-Bohm
(AB - h/e) oscillations are found to be dominant, contingent upon the surface
confinement of electrons in the nanowire. We also numerically study disordered
nanowires of finite length, bridging a gap in the existing literature. By
varying the nanowire length and disorder strength, we identify the transition
where Al'tshuler-Aronov-Spivak (AAS - h/2e) oscillations start dominating,
noting the effects of considering an open system. Moreover, we demonstrate how
the relative magnitudes of the scattering length and the device dimensions
govern the relative dominance of these harmonics with energy, revealing that
the AAS oscillations emerge and start dominating from the center of the band,
much higher in energy than the conduction band-edge. We also show the ways of
suppressing the oscillatory components (AB and AAS) to observe the
non-oscillatory weak localization corrections, noting the interplay of
scattering, incoherence/dephasing, the geometry of electronic distribution, and
orientation of magnetic field. This is followed by a study of surface roughness
which shows contrasting effects depending on its strength and type, ranging
from magnetic depopulation to strong AAS oscillations. Subsequently, we show
that dephasing causes a progressive degradation of the higher harmonics,
explaining the re-emergence of the AB component even in long and disordered
nanowires. Lastly, we show that our model qualitatively reproduces the
experimental magneto-conductance spectrum in [Holloway et al, PRB 91, 045422
(2015)] reasonably well while demonstrating the necessity of
spatial-correlations in the disorder potential, and dephasing.
