Lighting and displays accounts for a major part of our energy consumption, and presently light emitting diodes are penetrating the market. A first political incentive towards developing more efficient devices was taken by abolishing incandescent lamps. However, much more efficient and longer lifetime lighting devices are present today, constructed by use of semiconductor based light emitting diodes. By employing NW technology, further improvement in efficiency, material consumption and material tuning can be achieved and the important application area of ultra-bright and high-resolution displays directly benefits by this nano-materials approach.
Multiplet platelet LEDs emitting in blue, green and red. Photo: Olof Hultin
Nanowire light emitting diodes
Nanowire (NW) based light emitting diodes (LEDs) are most efficiently constructed in the so called core-shell configuration, where the different materials in the hetero-junction diode structure are stacked radially on each other. This gives a large effective emitting area with a small device footprint. The active region of the device is well protected from surface effects by the outer layers. The substrate can serve as one contact in the case of a conducting substrate (like Si), for a resistive substrate (like sapphire) a conducting buffer layer on top of the substrate serves as bottom contact layer. The top contact is preferably built from a transparent material, such as a transparent conducting oxide (TCO). A LED is typically made from an area of thousands of individual NW-LEDs in parallel. Lift-off techniques may be used to eliminate the substrate in the production process.
Nanowire-based microLEDs for display and lighting applications
At present, very strong efforts world-wide are focused on the possibility to replace virtually all display applications by microLEDs, as a next step after the market dominance of, first, liquid crystal based displays and, later, by OLEDs i.e. organic LEDs. In microLED display applications three basic colors, i.e. Blue, Green and Red, are produced by optimally designed InGaN-LEDs, with dimensions such that the entire pixel is of the order, or smaller than, 10 µm. Such displays have inherent much higher brightness and efficiency than today’s technologies and are ideally suited for applications in the areas of VR/AR (virtual/augmented reality) or HUD (head up displays for cars and aeroplanes). For this research we focus on sub-micron platelets of dislocation-free InGaN platelets enabling the direct and efficient emission of, not only blue, but also green and red emission, all without the use of phosphor technology. We are, at the same time, investigating these RGB-controlled LEDs for, so called, bio-centric lighting, by which the optimal color temperature can be obtained for various environmental situations. As a smaller, but important, area of LED applications, we carry on a minor effort in the field of UV-emitting LEDs of primary importance for water disinfection and general sterilization. This research is performed in collaborations with Glo AB, Brainlit AB, Watersprint AB and SAAB AB.
Nanowire carrier diffusion induced light emitting diodes.
Here we are working towards a nanowire light emitting diode architecture where the active parts do not have to be directly sandwiched in between electrical contacts but carrier diffusion from a higher band gap material into a lower band gap nanowire material can lead to highly polarized, directional and efficient luminescence. This is inspired by the work on carrier diffusion induced luminescence in thin films done at the Aalto University in Finland.
Nanowire-Based Visible Light Emitters, Present Status and Outlook. Monemar, B.; Ohlsson, B.J.; Gardner, N.F.; Samuelson, L., Semiconductors and Semimetals, Vol 94, 2016, 227-271. DOI: 10.1016/bs.semsem.2015.10.002
See article nanowire-based visible light at publisher's site
Self-assembled InN quantum dots on side facets of GaN nanowires. Bi, Z.X.; Ek, M.; Stankevic, T.; Colvin, J.; Hjort, M.; Lindgren, D.; Lenrick, F.; Johansson, J.; Wallenberg, L. R.; Timm, R.; Feidenhans´l, R.; Mikkelsen, A.; Borgström, M. T.; Gustafsson, A.; Ohlsson, B. J.; Monemar, B.; Samuelson, L., Journal of Applied Physics 2018, 123, 164302. DOI: 10.1063/1.5022756
See article self-assembled InN quantum dots at publisher's site
High In-content InGaN nano-pyramids: Tuning crystal homogeneity by optimized nucleation of GaN seeds. Bi, Z.X.; Gustafsson. A.; Lenrick, F.; Lindgren, D.; Hultin, O.; Wallenberg, L. R.; Ohlsson, B. J.; Monemar, B.; Samuelson, L., Journal of Applied Physics 2018, 123, 025102. DOI: 10.1063/1.5010237
See article high In-content at publisher's site
InGaN platelets: synthesis and applications towards green and red light emitting diodes. Bi, Z.X.; Lenrick, F.; Colvin, J.; Gustafsson, A.; Hultin, O.; Nowzari, A.; Lu, T.; Wallenberg, R.; Timm, R.; Mikkelsen, A.; Ohlsson, J. B.; Storm, K.; Monemar, B; Samuelson. L.; Nano Lett. 2019, 19, 5, 2832-2839, DOI: 10.1021/acs.nanolett.8b04781
See article InGaN platelets at publisher's site
- Zhaoxia Bi
- Magnus Borgström
- Anders Gustafsson
- Dan Hessman
- Anders Mikkelsen
- Bo Monemar
- Mats-Erik Pistol
- Lars Samuelson
- Reine Wallenberg
Olof Hultin, Nanostructures for optoelectronics Device Fabrication and Characterization, PhD thesis, Lund University 2018
See Olof Hultin's thesis at the Research Portal
Ali Nowzari, Junction Engineering in Nanostructured Optoelectronic Devices, PhD thesis, Lund University 2018
See Ali Nowzari's thesis at the Research Portal
Research focussed on nanowires and molecular engineering to find new solutions for energy
Other Major Projects
VR/SEA-project 43610-1 “Nanowire-based light emitting diodes with multiple wave-lengths in the visible range”