We optimized p++-GaInN/n++-GaN tunnel junctions grown on conventional light-emitting diodes, corresponding to n–p–n structures. We investigated two dependences at the tunnel junctions, the InN mole fraction dependence and a doping dependence. The lowest voltage drop at the reverse-biased tunnel junction was 0.68 V at 20 mA with a 3 nm p++-Ga0.8In0.2N (Mg: 1×1020 cm-3)/30 nm n++-GaN (Si: 4×1020 cm-3) structure. We then found that the Mg memory effect was reasonably suppressed by using the p++-GaInN instead of a p++-GaN. At the same time, the amount of Si doping in the following n++-GaN should be substantially high to overcome the Mg memory effect.