III-nitride blue light-emitting diodes utilizing hybrid tunnel junction with low excess voltage

Abstract

Tunnel junctions (TJs) offer alternative designs and promise in some cases improved performances for nitride-based light-emitting diode (LEDs) and laser diodes (LDs) and are widely used in academic studies. However, the voltage penalty of the LEDs and LDs, in comparison with standard contact technologies, has been a major concern especially for commercial applications. In this study, we investigated methods to achieve low excess voltage. Using ammonia molecular beam epitaxy (NH3 MBE), GaN TJs were grown on commercial metalorganic chemical vapor deposition (MOCVD) grown blue LED wafers. Atom probe tomography (APT) and secondary ion mass spectrometry (SIMS) indicate 1 min buffered HF (BHF) clean of the regrowth interface reduced Mg and impurity incorporation into the n++ regrown TJ layers. The wafers were processed and measured in parallel to reference wafers using both university processes and industry processes. At 20 A cm−2, TJ LEDs grown with Si δ-doping at the junction interface processed in the university cleanroom had a forward voltage of 3.17 V in comparison to 2.86 V for LEDs processed with a standard indium tin oxide (ITO) contact. Unencapsulated TJ LEDs processed by industrial process without ITO or current blocking layer had about 0.3 V excess voltage compared to reference LEDs. The TJ LEDs also had more uniform light emission profile. The low excess voltage and consistent results acquired in both settings suggest that TJ can be scaled for industrial processes.