12 August 2021
MOCVD tunnel junctions beat ITO for blue μLEDs
University of California Santa Barbara (UCSB) has demonstrated micro-scale blue light-emitting diodes (μLEDs) with metal-organic chemical vapor deposition (MOCVD) tunnel junction (TJ) contacts with peak external quantum efficiency (EQE) and wall-plug efficiency (WPE) significantly higher than devices using indium tin oxide (ITO) [Matthew S. Wong et al, Appl. Phys. Express, vol14, p086502, 2021].
UCSB has been developing MOCVD GaN TJs for some time. In July, we reported on UCSB’s work in using MOCVD TJs to stack blue and green LEDs [www.semiconductor-today.com].
A key problem with TJ contacts in indium gallium nitride (GaN) LEDs is that the p-side of the device becomes buried under n-GaN material. This makes it difficult to activate the magnesium doping that provides acceptor levels that grab electrons out of the valence band, creating mobile positively-charged holes in the p-GaN layers.
The researchers comment: “The higher WPE performance at low current density was attributed to the greater light output power (LOP), where the voltage penalty was relatively low and the enhancement in LOP was significant, and the increase in WPE diminished with current density.”
The author Mike Cooke is a freelance technology journalist who has worked in the semiconductor and advanced technology sectors since 1997.