  Statistical studies of X-ray selected Active Galactic Nuclei (AGN) indicate
that the fraction of obscured AGN increases with increasing redshift, and the
results suggest that a significant part of the accretion growth occurs behind
obscuring material in the early universe. We investigate the obscured fraction
of highly accreting X-ray AGN at around the peak epoch of supermassive black
hole growth utilizing the wide and deep X-ray and optical/IR imaging datasets.
A unique sample of luminous X-ray selected AGNs above $z>2$ was constructed by
matching the XMM-SERVS X-ray point-source catalog with a PSF-convolved
photometric catalog covering from $u^*$ to 4.5$\mu \mathrm{m}$ bands.
Photometric redshift, hydrogen column density, and 2-10 keV AGN luminosity of
the X-ray selected AGN candidates were estimated. Using the sample of 306 2-10
keV detected AGN at above redshift 2, we estimate the fraction of AGN with
$\log N_{\rm H}\ (\rm cm^{-2})>22$, assuming parametric X-ray luminosity and
absorption functions. The results suggest that $76_{-3}^{+4}\%$ of luminous
quasars ($\log L_X\ (\rm erg\ s^{-1}) >44.5$) above redshift 2 are obscured.
The fraction indicates an increased contribution of obscured accretion at high
redshift than that in the local universe. We discuss the implications of the
increasing obscured fraction with increasing redshift based on the AGN
obscuration scenarios, which describe obscuration properties in the local
universe. Both the obscured and unobscured $z>2$ AGN show a broad range of SEDs
and morphology, which may reflect the broad variety of host galaxy properties
and physical processes associated with the obscuration.
