  Tuning the ambipolar behavior in charge carrier transport via
defect-engineering is crucial for achieving high mobility transistors for
nonlinear logic circuits. Here, we present the electric-field tunable electron
and hole transport in a microchannel device consisting of highly air-stable van
der Waals (vdW) noble metal dichalcogenide (NMDC), PdSe$_\mathrm{2}$, as an
active layer. Pristine bulk PdSe$_\mathrm{2}$ constitutes Se surface vacancy
defects created during the growth or exfoliation process and offers an
ambipolar transfer characteristics with a slight electron dominance recorded in
field-effect transistor (FET) characteristics showing an ON/OFF ratio < 10 and
electron mobility ~ 21 cm$^2$/V.s. However, transfer characteristics of
PdSe$_\mathrm{2}$ can be tuned to a hole-dominated transport while using
hydrochloric acid (HCl) as a $p$-type dopant. On the other hand, the chelating
agent EDTA, being a strong electron donor, enhances the electron-dominance in
PdSe$_\mathrm{2}$ channel. In addition, $p$-type behavior with a 100 times
higher ON/OFF ratio is obtained while cooling the sample down to 10 K.
Low-temperature angle-resolved photoemission spectroscopy resembles the
$p$-type band structure of PdSe$_\mathrm{2}$ single crystal. Also, first
principle density functional theory calculations justify the tunability
observed in PdSe$_\mathrm{2}$ as a result of defect-engineering. Such a
defect-sensitive ambipolar vdW architecture may open up new possibilities
towards future CMOS (Complementary Metal-Oxide-Semiconductor) device
fabrications and high performance integrated circuits.
