  We studied models of leptogenesis where three right-handed Majorana neutrinos
are involved and the minimal-extended seesaw mechanism including an additional
singlet field produces four light neutrinos. This study shows that the type of
mass ordering and heavy Majorana scales can be determined by inputting the
simplest orthogonal matrix into the Casas-Ibarra(CI) representation of seesaw.
The CP asymmetry produced from the decays of heavy neutrinos and the dilution
mass are predicted in terms of the mass and mixing elements of the fourth
neutrino. Upon the choice of CI matrix, the existence of a light sterile
neutrino is required to explain the high-energy lepton asymmetry in light of
phenomenological measurements. Although there are several free parameters
attributable to an additional neutrino, the model can be in part constrained by
low-energy experiments such as sterile neutrino searches and neutrinoless
double-beta decays, as well as the observed baryon asymmetry in the universe.
