Spin-orbit gap feature in energy dispersion of
one-dimensional devices is revealed via strong spin-orbit interaction
(SOI) effects under Zeeman field. We describe the utilization
of a finger-gate or a top-gate to control the spin-dependent
transport characteristics in the SOI-Zeeman influenced split-gate
devices by means of a generalized spin-mixed propagation matrix
method. For the finger-gate system, we find a bound state in
continuum for incident electrons within the ultra-low energy regime.
For the top-gate system, we observe more bound-state features
in conductance associated with the formation of spin-associated
hole-like or electron-like quasi-bound states around band thresholds,
as well as hole bound states around the reverse point of the
energy dispersion. We demonstrate that the spin-dependent transport
behavior of a top-gate system is similar to that of a finger-gate system
only if the top-gate length is less than the effective Fermi wavelength.