Anisotropic charge carrier transport in free-standing hexagonal boron nitride thin films

The in-plane and out-of-plane mobility–lifetime products of electrons and holes in free-standing hexagonal boron nitride (hBN) films are extracted from current–voltage characteristics of metal–hBN–metal structures measured under external excitations. The in-plane mobility–lifetime products for electrons and holes are ∼2.8 × 10−5 and ∼4.85 × 10−6 cm2/V, measured from lateral carrier collection, whereas the out-of-plane mobility–lifetime products for electrons and holes are ∼5.8 × 10−8 and ∼6.1 × 10−9 cm2/V, measured from vertical carrier collection, respectively. The mobility–lifetime product is a few orders of magnitude higher along the plane than along the out of plane in hBN films.