Tunnel-injected sub 290 nm ultra-violet light emitting diodes with 2.8% external quantum efficiency

Abstract

We report on the high efficiency tunnel-injected ultraviolet light emitting diodes (UV LEDs) emitting at 287 nm. Deep UV LED performance has been limited by the severe internal light absorption in the p-type contact layers and low electrical injection efficiency due to poor p-type conduction. In this work, a polarization engineered Al 0.65 Ga 0.35 N/In 0.2 Ga 0.8 N tunnel junction layer is adopted for nonequilibrium hole injection to replace the conventionally used direct p-type contact. A reverse-graded AlGaN contact layer is further introduced to realize a low resistance contact to the top n-AlGaN layer. This led to the demonstration of a low tunnel junction resistance of 1.9 Â 10 À3 X cm 2 obtained at 1 kA/cm 2. Light emission at 287 nm with an on-wafer peak external quantum efficiency of 2.8% and a wall-plug efficiency of 1.1% was achieved. The measured power density at 1 kA/cm 2 was 54.4 W/cm 2 , confirming the efficient hole injection through interband tunneling. With the benefits of the minimized internal absorption and efficient hole injection, a tunnel-injected UV LED structure could enable future high efficiency UV emitters.

AlGaN‐based ultraviolet light‐emitting diodes: challenges and opportunities

“…The EQE achieved in the tunnel‐injected device was 2.8% at an emission wavelength of 287 nm. [ 73 ] Ni et al compared the growth of single layer of AlN template by MOCVD method and by high temperature annealed (HTA) sputtering method on the sapphire substrate. The obtained output power and EQE without the MOCVD growth method was 9.38 mW at an injection current of 100 mA and 2.77% at a current of 30 mA for an emission wavelength of 297.5 nm.…”

Progress in External Quantum Efficiency for III‐Nitride Based Deep Ultraviolet Light‐Emitting Diodes

“…According to the research results by different groups, however, the external quantum efficiency (EQE) is still lower than 10% for DUV LEDs when the peak emission wavelength is shorter than 280 nm, and most of the reported efficiency droop is higher than 10% for the LEDs at deep ultraviolet range [see Figure (a,b)]. DUV LEDs with low EQE and significant efficiency droop effect cannot efficiently kill all the bacteria in the drinking water with high flow rate . As a result, before the massive penetration into the market to replace the conventional mercury based deep ultraviolet light source, it is essentially important to enhance the EQE for DUV LEDs.…”

“…Summary of the reported (a) EQE and (b) efficiency droop for DUV LEDs by different groups during the last 5 years (2014–2018) …”

“…On the other hand, the TM‐polarized optical photons for DUV LEDs make the mechanism of the light propagation unique, such that the TM‐polarized light tends to escape from the sidewalls for the devices . Meanwhile, the strong optical absorption for DUV photons arises from the passive layers with the smaller energy band gap and the absorptive contact metal further reduces the LEE . Therefore, tremendous efforts shall be made to improve both the IQE and the LEE for DUV LEDs.…”

226 nm AlGaN/AlN UV LEDs using p-type Si for hole injection and UV reflection

“…To enhance the hole injection of UV LEDs, tunneling junctions were investigated recently: n-AlGaN/InGaN/p-AlGaN, 20,26 metal/InGaN/p-AlGaN, 27 and n-GaN/Al/p-AlGaN 28 (see supplementary material Table I for a summary). However, the use of an n-AlGaN top contact layer was reported to hinder hydrogen diffusion, making it more difficult for Mg activation in the p-AlGaN layer.…”