  We report on the design and demonstration of polarization-engineered
GaN/InGaN/GaN tunnel junction diodes with high current density and low
tunneling turn-on voltage. Wentzel-Kramers-Brillouin (WKB) calculations were
used to model and design tunnel junctions with narrow bandgap InGaN-based
barrier layers. N-polar p-GaN/In0.33Ga0.67N/n-GaN heterostructure tunnel diodes
were grown using molecular beam epitaxy. Efficient zero bias tunneling turn-on
with a high current density of 118 A/cm2 at a reverse bias of 1V, reaching a
maximum current density up to 9.2 kA/cm2 were obtained. These results represent
the highest current density reported in III-nitride tunnel junctions, and
demonstrate the potential of III-nitride tunnel devices for a broad range of
optoelectronic and electronic applications.
