GaN tunnel junctions (TJs) are grown by ammonia molecular beam epitaxy. High doping levels are achieved with a net acceptor concentration close to similar to 10(20) cm(-3), thanks to the low growth temperature. This allows for the realization of p-n junctions with ultrathin depletion width enabling efficient interband tunneling. n-p-n structures featuring such a TJ exhibit low leakage current densities, e.g., <5 x 10(-5) A cm(-2) at reverse bias of 10 V. Under forward bias, the voltage is 3.3V and 4.8V for current densities of 20A cm(-2) and 2000A cm(-2), respectively. The specific series resistance of the whole device is 3.7 x 10(-4) Omega cm(2). Then micro-light emitting diodes (mu-LEDs) featuring buried TJs are fabricated. Excellent current confinement is demonstrated together with homogeneous electrical injection, as seen on electroluminescence mapping. Finally, the I-V characteristics of mu-LEDs with various diameters point out the role of the access resistance at the current aperture edge. (C) 2015 AIP Publishing LLC.