Low-resistance tunnel junctions on GaAs substrates using GaInNAs

Using molecular-beam epitaxy, we have fabricated $p-n$ tunnel junctions lattice matched to GaAs substrates that consist of highly C-doped $Ga0.93In0.07As$ on the $p$ side, and highly Si-doped $Ga0.93In0.07N0.02As0.98$ on the $n$ side. The introduction of N on the $n$ side of the tunnel junction: (1) lowers the conduction band edge while leaving the valence band edge unchanged, (2) allows the introduction of In to further lower the band gap while remaining lattice matched to GaAs, and (3) increases the maximum Si donor activation that can be achieved. All three of these effects increase the tunneling probability for carriers across the junction and decrease the specific resistance. We estimate the active C acceptors on the $p$ side to be $1.5×1020 cm−3$ and the active Si donors on the $n$ side to be $1.8×1019 cm−3.$ Because of the mutual passivation effect between N and Si atoms, the Si doping level was increased to $1.0×1020 cm−3$ to achieve this active net donor concentration. The specific resistance of test tunnel junctions has been measured to be $<1×10−5 Ω cm2$ corresponding to $<0.1 V$ drop at a current density of $10 kA/cm2.$ These results are a substantial improvement over corresponding test structures without N on the $n$ side of the junction. The experimental results are in good agreement with model calculations.