We report on III-nitride-based micro-light-emitting diodes (µLEDs) operating at 450 nm wavelength with diameters down to 2 µm. Devices with a standard LED structure followed by a tunnel junction were grown by plasma-assisted molecular beam epitaxy. The emission size of µLEDs was defined by shallow He+ implantation of the tunnel junction region. The ion implantation process allows to create flat devices, applicable to further epitaxial regrowth. The shift of current density for the maximum external quantum efficiency as a function of µLEDs diameter was observed. This effect may be a fingerprint of the change in the external efficiency related to the lateral carrier diffusion (limited by holes) in InGaN quantum wells.