Sep 1, 2010
GaN-nanoworld shaped to optimize optoelectronics
GaN nanorods (NRs) could push optoelectronic devices further towards their efficiency limits. The shape and the arrangement of these nanometre-sized crystals can significantly influence the properties of LEDs. As experiments show, both parameters can be adjusted by accurate patterning of the substrate via nanoimprint lithography and by tuning of the carrier gas composition.
Researchers from the Institute of Semiconductor Technology at Braunschweig Technical University, the Paul Drude Institute in Berlin and OSRAM Opto Semiconductors in Regensburg have teamed up to study the growth of GaN nanorods with incorporated optically active InGaN quantum wells. Shaping of the nanostructures from pyramids to pencil-shaped nanocrystals to hexagonal rods has been achieved by the adjusting the hydrogen content within the H2/N2 carrier gas mixture during the metal-organic chemical vapour deposition (MOCVD) process.
The scientists have found a way to grow these structures in a standard large volume MOCVD system without using any catalyst or pulsed growth mode. Transmission electron micrographs (TEM) showed the morphological properties of the nanorods and the relation between lateral growth rate and semipolar side facets. Additionally, the growth of InGaN multiple quantum wells (MQW) on different side facets was successfully confirmed and cathodoluminescence measurements revealed different emission wavelengths from different parts of the nanorods.
Growth on silicon substrates and the combination of nanoemitters with integrated electronic and photonic circuits is our vision for the future. What's more, the growth of highly efficient InGaN QWs on defect-free nanorod surfaces and the possibility to cover the tremendously increased surface with an active layer would enable more light output per substrate area for a bright future.
The researchers presented their work in the journal Nanotechnology.
About the author
The collaborating teams are partners within the MONALISA research project (01BL0811) funded by the Federal Ministry of Education and Research (BmBF). Werner Bergbauer is a PhD student at OSRAM OS and the Institute of Semiconductor Technology (IHT), Braunschweig Technical University. Christopher Kölper, another PhD student, Dr Martin Strassburg and Dr Norbert Linder supported the NR research activities at OSRAM OS. Prof. Dr Andreas Waag is head of the IHT in Braunschweig and is responsible for spintronic, wide-bandgap semiconductors and nanostructures. In his group assistant professor Dr Hergo-Heinrich Wehmann is supporting the MOVPE experiments. Sönke Fündling is a PhD student and Dr Shunfeng Li a postdoc for epitaxy at IHT. Additionally, PhD student Jonas Lähnemann and Dr Claudia Roder from the PDI Berlin performed cathodoluminescence and TEM measurements supported by Dr Achim Trampert, head of the microstructure department.