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The phenomenon of resonant tunneling transport through polar double-barrierheterostructures is systematically investigated using a combined experimentaland theoretical approach. On the experimental side, GaN/AlN RTDs are grown byMBE. In-situ electron diffraction is employed to monitor the number ofmonolayers incorporated into each tunneling barrier. Using this preciseepitaxial control at the monolayer level, we demonstrate exponential modulationof the resonant tunneling current as a function of barrier thickness. Both thepeak voltage and characteristic threshold bias exhibit a dependence on barrierthickness as a result of the intense electric fields present in the polarheterostructures. To get further insight into the asymmetric tunnelinginjection, we present an analytical theory for tunneling transport across polarheterostructures. A general expression for the resonant tunneling current withcontributions from coherent and sequential tunneling processes is introduced.After applying this theory to the case of GaN/AlN RTDs, their experimentalcurrent-voltage characteristics are reproduced over both bias polarities, withtunneling currents spanning several orders of magnitude. This agreement allowsus to elucidate the role played by the internal polarization fields on themagnitude of the tunneling current and broadening of the resonant line shape.Under reverse bias, we identify new tunneling features originating from highlyattenuated resonant tunneling phenomena, which are completely captured by ourmodel. Our analytical model, provides a simple expression which reveals theconnection between the polar RTD design parameters and its current-voltagecharacteristics. This new theory paves the way for the design of polar resonanttunneling devices exhibiting efficient resonant current injection and enhancedtunneling dynamics, as required in various practical applications.

Broken Symmetry Effects due to Polarization on Resonant Tunneling Transport in Double-Barrier Nitride Heterostructures