Low p-contact resistance InGaN-capped AlGaN-based DUV LEDs on bulk AlN substrates

Better wall plug efficiency of deep-ultraviolet light emitting diodes (DUV-LEDs) requires simultaneous low resistivity p-type and n-type contacts, which is a challenging problem. In this study, the co-optimization of p-InGaN and n-AlGaN contacts for DUV LEDs is investigated. We find that using a thin In0.07Ga0.93N cap is effective in achieving ohmic p-contacts with specific contact resistivity of 3.10 × 10−5Ω cm2. Upon monolithic integration of p- and n-contacts for DUV LEDs, we find that the high-temperature annealing of 800 °C required for the formation of low resistance contacts to n-AlGaN severely degrades the p-InGaN layer, thereby reducing the hole concentration and increasing the specific contact resistivity to 9.72 × 10−4Ω cm2. Depositing a SiO2 cap by plasma-enhanced atomic layer deposition (PE-ALD) prior to high-temperature n-contact annealing restores the low p-contact resistivity, enabling simultaneous low-resistance p- and n-contacts. DUV-LEDs emitting at 268 nm fabricated with the SiO2 capping technique exhibit a 3.5 V reduction in operating voltage at a current level of 400 A/cm2 and a decrease in differential ON-resistance from 6.4 to 4.5 m Ω cm2. This study highlights a scalable route to high-performance, high-Al-content bipolar AlGaN devices.