The role of Mg bulk hyper-doping and delta-doping in low-resistance GaN homojunction tunnel diodes with negative differential resistance

GaN p⁺⁺/n⁺⁺ tunnel junctions (TJs) with heavy bulk or delta Mg doping at the junction were grown via molecular beam epitaxy with a hysteresis-free and repeatable negative differential resistance (NDR). The TJ with Mg doping of 5.5 × 10²⁰ cm^-3 shows NDR at ∼1.8 V and a large current density of 3.4 KA/cm² at -1.0 V. Atomic resolution scanning transmission electron microscopy imaging showed no additional defects despite the doping exceeding the solubility limit in GaN allowing subsequent epitaxy of series-connected layers and devices. GaN homojunction TJs grown on bulk GaN showed an improved current density and NDR stability. In addition, the effect of Mg delta doping at the junction was investigated for the first time showing a dramatic improvement in the tunneling characteristics. A metal-organic chemical vapor deposition (MOCVD) grown InGaN light-emitting diode (LED) with an MBE grown GaN homojunction tunnel contact to the MOCVD grown p-GaN layer shows superior lateral conductivity and improved luminescence uniformity, but suffers an added voltage penalty, assumed to be due to interface impurities, compared to control LED with indium-tin-oxide.