  The non-centrosymmetric semiconductor BiTeI exhibits two distinct surface
terminations that support spin-split Rashba surface states. Their ambipolarity
can be exploited for creating spin-polarized $p$-$n$ junctions at the
boundaries between domains with different surface terminations. We use scanning
tunneling microscopy/spectroscopy (STM/STS) to locate such junctions and
investigate their atomic and electronic properties. The Te- and I-terminated
surfaces are identified owing to their distinct chemical reactivity, and an
apparent height mismatch of electronic origin. The Rashba surface states are
revealed in the STS spectra by the onset of a van Hove singularity at the band
edge. Eventually, an electronic depletion is found on interfacial Te atoms,
consistent with the formation of a space charge area in typical $p$-$n$
junctions.
