  In mesoscopic electronic systems, the Fabry-P\'{e}rot (FP) oscillation is
observed in various 1D devices. As for higher dimensions, numerous transverse
channels usually lead to dephasing that quenches the overall oscillation of the
conductance. Up to now, the FP oscillation in 2D electronic systems is only
reported in graphene-based devices, and very recently, the \emph{pn} junctions
of inverted InAs/GaSb double quantum well [Phys. Rev. X 10, 031007 (2020)]. In
the latter, the band shape of a sombrero hat plays an essential role, which
introduces a novel mechanism of electron-hole hybridization for the 2D FP
oscillation. In this work, we propose that such a scenario can be generalized
to the 2D planar junction composed of low-density Rashba gas, where the band
bottom possesses a sombrero hat shape as well. We show that the backscattering
between the outer and inner Fermi circles dominates the FP interference and
significantly suppresses the dephasing effect between different transverse
channels, which leads to a visible oscillation of the tunneling conductance.
Specially, the visibility of the oscillating pattern can be enhanced by
applying interface barriers, in contrast to that in the InAs/GaSb double
quantum well. Our results provide a promising way for the implementation of the
FP oscillation in the 2D electron gas.
