Dielectric assisted liftoff enabled simultaneous low n- and p- differential contact resistivities in ultrawide bandgap AlGaN pn diodes on bulk AlN

Abstract Ultrawide bandgap (UWBG) semiconductor pn junction diodes are desired for high voltage power electronics and UV optoelectronic devices. Making low-resistance contacts to the UWBG junction region is difficult due to low solubility of dopants in AlGaN, nonavailability of readily available metals with suitable work functions, processing induced damage and the lack of dislocations in single-crystal bulk AlN substrates. We report dielectric assisted liftoff, a processing scheme to simultaneously achieve n- and p-contacts with low turn-on voltages ( v on ), and low specific differential contact resistances ( ϱ c ) in heterostructure diodes on bulk AlN. We report ϱ c n = 5–6 × 10 −5 Ωcm 2 and v on n ≈ 0 V to etched n-type Al 0.75 Ga 0.25 N for current densities between 0 and 5 kA cm −2 . We also report ϱ c p ≈ 10 −3 –10 −5 Ω cm 2 and v on p ≈ 0–0.01 V to p-In 0.07 Ga 0.93 N contacts over the same current range. The key design principle in fabrication of the diodes is to avoid exposing the nitride semiconductor surfaces to photoresist by using a dielectric layer, which also simultaneously protects the p-InGaN during the n-contact annealing step.