News Article
Phosphide based nanostructures could be used as LEDs
InAsP segments embedded in indium phosphide nanowires emit light, whose direction can be altered by adjusting the position of the InAsP active region.
Researchers from Netherlands based FOM Institute AMOLF, together with colleagues from Philips Research, Eindhoven University of Technology and Delft University of Technology, have made special compound semiconductor nanostructures that could be used as LEDs.
The scientists, led by Jaime Gomez Rivas, have demonstrated the directional emission of light by InAsP segments embedded in InP nanowires. The nanowires are arranged in a periodic array, forming a 2D photonic crystal slab.
Figure 1. Electron microscope image of InP nanowires
Controlling the direction of the light is vitally important for increasing LED efficiency. The direction in which a LED emits light is mainly determined by the surface between the LED and the surrounding air. As light can only escape from the LED at small angles, the direction of emission is usually straight on (perpendicular to the surface).
Figure 2. Diagram of the light intensity. Measurement of the intensity of the light emitted by the nanowires as a function of the wavelength (i.e. colour) and the angle of the light emitted. The maximum depends on the emitter, which is located in the nanowires. In this case it is at 950 nm and 55 degrees.
However this can be influenced by nanostructures in the surface of the LED. Inspired by these nanostructures, the researchers have developed a new technology with which the direction of the light can be changed.
The new method consists of growing partially-emitting nanowires in an ordered pattern. This pattern forms a ‘photonic crystal’ that sends the light in specific directions. Furthermore, the researchers have shown that the emission can be optimised by a smart positioning of the emitting part within the nanowire.
This knowledge could lead to an increased efficiency of LEDs. Moreover, the researchers say it provides opportunities for a next generation of LEDs, based on semiconducting nanowires.
This research is part of the Industrial Partnership Programme 'Improved solid-state light sources' of the Foundation for Fundamental Research on Matter (FOM) and Philips and the FOM Programme 'NanoPhotovoltaics'. It also received support from Technology Foundation STW.
Further details of this work can be obtained from the paper entitled, 'Controlling the directional emission of light by periodic arrays of heterostructured semiconductor nanowires', by Diedenhofen et al in ACS Nano (2011), doi: 10.1021/nn201557h.
