  Bi$_{2}$Se$_{3}$, one of the most widely studied topological insulators
(TIs), is naturally electron-doped due to n-type native defects. However, many
years of efforts to achieve p-type Bi$_{2}$Se$_{3}$ thin films have failed so
far. Here, we provide a solution to this long-standing problem, showing that
the main culprit has been the high density of interfacial defects. By
suppressing these defects through an interfacial engineering scheme, we have
successfully implemented p-type Bi$_{2}$Se$_{3}$ thin films down to the
thinnest topological regime. On this platform, we present the first tunable
quantum Hall effect (QHE) study in Bi$_{2}$Se$_{3}$ thin films, and reveal not
only significantly asymmetric QHE signatures across the Dirac point but also
the presence of competing anomalous states near the zeroth Landau level. The
availability of doping tunable Bi$_{2}$Se$_{3}$ thin films will now make it
possible to implement various topological quantum devices, previously
inaccessible.
