High current density ultrawide-bandgap AlGaN pn diodes with dopant-free distributed polarization-doped junction regions

We report high-current-density AlGaN pn diodes grown on bulk AlN substrates by molecular beam epitaxy. AlGaN layers with linearly graded Al composition between 70% and 95% are utilized for both n- and p-type regions. The dopant-free pn junction depletion region is accessed by impurity doped n- and p-contact layers. The diodes exhibit a low specific on-resistance of 0.14 mΩ cm2 and achieve current densities, J exceeding 20 kA/cm2 at 10 V, representing one of the lowest resistances reported for high Al-content AlGaN pn diodes. Capacitance–voltage measurements yield a built-in potential of 5.5 V and carrier concentrations of the order of 1018 cm−3 without impurity doping. Enabled by the low ideality factor ηmin = 1.64 of the diodes, analytical models for diffusion and Shockley–Read–Hall recombination current density could be fitted to the experimental J–V. Electroluminescence measurements reveal deep-ultraviolet emission with a peak wavelength of 240 nm, highlighting radiative recombination within high Al-content layers. These results demonstrate the potential of fully polarization-doped AlGaN pn junctions for high-power and high-frequency ultrawide-bandgap electronic and optoelectronic devices.