Coherent Resonant Tunneling Transport through Non-centrosymmetric GaN/AlN Multi-barrier Heterostructures*

The recent demonstration of resonant tunneling through double barrier GaN/AlN heterostructures has reignited interest in harnessing this quantum transport regime for ultrafast electronic and photonic devices. In noncentrosymmetric semiconductors, however, quantum confinement results not only in a discontinuous band profile, but also generates built-in polarization charges along the transport direction. Here, using a combined experimental and theoretical approach, we elucidate the important consequences of the built-in polarization fields on the resonant tunneling transport characteristics of multiple-barrier GaN/AlN heterostructures.

A set of GaN/AlN multi-barrier heterostructures, with increasing number of barriers N={1,2,3,4}, is grown by molecular beam epitaxy. Room temperature current-voltage characteristics reveal a marked asymmetry in the tunneling current with respect to the bias polarity. This effect is a direct consequence of the internal polarization charges in the active region, which lack inversion symmetry. Under forward bias, multiple resonances and negative differential conductance are measured, attesting to the highly coherent electronic transport. Under reverse bias, tunneling currents exhibit an exponential attenuation as the number of barriers increases. Moreover, a polarization-induced threshold voltage which scales linearly with the number of barriers is identified, in agreement with our quantum transport model for III-Nitride heterostructures.