DenBaars "Improving MOCVD Tunnel Junctions"
Prof. Steve DenBaars part of UCSB research team improving MOCVD tunnel junctions for gallium nitride μ-light emitting diodes
University of California Santa Barbara (UCSB) in the USA claims the lowest forward voltage for gallium nitride (GaN)-based micro-sized light-emitting diodes (μLEDs) with epitaxial tunnel junctions (TJs) grown by metal-organic chemical vapor deposition (MOCVD) [Panpan Li et al, Optics Express, vol28, p18707, 2020]. The voltage was only marginally higher than that achieved with indium-tin oxide (ITO) transparent conductive electrodes.
The UCSB team used a selective-area growth (SAG) technique to create a tunnel junction layer with perforations. The perforated holes in the TJ were used to enable escape of hydrogen during annealing aimed at activating the underlying p-GaN layer of the junction. Hydrogen passivates the magnesium acceptor levels of the p-GaN, inhibiting their ability capture electrons and create holes in the valence band. Although molecular beam epitaxy (MBE) can be used to avoid hydrogen in GaN TJ structures, MOCVD is preferred for manufacturing.
Industry is looking to use μLEDs in a range of applications: “wearable devices, large-area displays, augmented reality (AR) and virtual reality (VR), and high-speed visible light communications (VLC),” are mentioned in the paper. The potential advantages of μLEDs over liquid crystal displays (LCDs) or organic LEDs include ultra-high resolution and lower power consumption.
Hoped for benefits of using TJ structures over conventional p-electrodes include simpler fabrication, improved current spreading, and lower photon absorption. New device architectures could be enabled with direct integration of blue/green/red μLEDs in cascade structures connected with TJs.