Sub 300 nm wavelength III-Nitride tunnel-injected ultraviolet LEDs

We report on the first demonstration of tunnel-injection-based III-Nitride ultraviolet light emitting diodes (LEDs) with emission wavelength lower than 300 nm. The III-Nitride system could enable a new class of solid state ultraviolet sources that could surpass the efficiency and cost of traditional gas-based ultraviolet bulbs. However, III-Nitride based ultraviolet emitters have significantly lower efficiency (10-100x lower) than visible wavelength emitters, even though the internal quantum efficiency (IQE) of AlGaN emitters is high. The main reason for the lower efficiency in these devices is the high acceptor activation energy, poor hole availability, and high p-contact resistance in p-type AlGaN. Interband tunnel junctions (TJ) can overcome these fundamental limitations by non-equilbrium injection of holes into the LED active region, offering an approach to increase both the electrical injection as well as light extraction efficiency. However, interband PN tunnel junctions become increasingly more resistive as the band gap is increased. We show here that polarization engineering can enable non-equilibrium hole injection into wide bandgap AlGaN with bandgap larger than 4.7 eV (Al composition > 50%), enabling UV LEDs at a wavelength of 295 nm, with a record low differential resistance of 1.6 × 10^-3 Ωcm² at a current density of 1 kA/cm².