The
difficulty of current injection into single-crystalline hexagonal
boron nitride (h-BN) has long hindered the realization
of h-BN-based high-performance electronic and optoelectronic
devices. Here, with the contact formed by Ar plasma treatment, Ni/Au
metal deposition, and subsequent high-temperature annealing, we demonstrate
current injection into single-crystalline h-BN with
a C doping level of ∼1.5 × 1019 atoms/cm3. A comparison to the current flow during the dielectric breakdown
of h-BN clearly verifies our current injection. The
devices show non-Ohmic conduction for all measured temperatures (20–598
K). Analysis of activation energies for carrier transport suggests
nearest-neighbor-hopping-assisted Poole–Frenkel (PF) conduction
in the highly defective h-BN at the contact region.
The estimated dominant defect level with the range of 240–720
meV is much smaller than the Schottky barrier height at the metal/h-BN interface, supporting the effective contact formation
for current injection. Moreover, structural and chemical characterizations
at the contact suggest that an interaction between Ni and defective h-BN introduces defect states in the gap, assisting the
current injection. In contrast, the characterizations confirm the
well-retained high crystallinity of h-BN in the channel,
indicating the potential of the present contact formation method for
the future development of high-performance h-BN-based
devices.