Mar 26, 2013
Acceptor-free single crystal phase InP nanowires
Semiconductor nanowires are fascinating structures that could benefit photonics and energy conversion, as well as quantum confined systems, but their desirable optical and electronic behaviours are often screened by polytypism or because of impurities incorporated during growth. Publishing their results in the journal Nanotechnology, researchers at Eindhoven University of Technology have shown that stacking fault-free wurtzite (WZ) and zincblende twinning superlattice (ZB TSL) InP nanowires (NWs) can be made nearly acceptor-free by combining high temperature growth and post-growth sidewall etching. The wires exhibit long carrier lifetimes and high photoluminescence (PL) efficiency up to room temperature, and exhibit great potential for nanowire devices.
We have shown that stacking fault-free WZ and ZB TSL can be grown by the vapour-liquid-solid (VLS) growth mechanism at a high growth temperature (540 °C). We emphasize that pure WZ and ZB TLS InP NWs were achieved without using dopants. Our WZ and ZB TSL NWs were simultaneously grown for different sizes of gold catalyst seeds, which provides useful input to a more complete understanding of InP NW growth and crystal structure formation.
Importantly, the high growth temperature together with in situ HCl etching to avoid sidewall growth provides high-optical-quality NWs. The WZ NWs do not show any acceptor-related emission, implying that the VLS-grown NW is almost impurity free due to sidewall removal by HCl. They only emit light at the free exciton (1.491 eV) and the donor-bound exciton transition (1.4855 eV) with very narrow linewidths of 1.5–2.0 meV.
The ZB NWs exhibit a PL spectrum that is unaffected by the twinning planes. Surprisingly, the acceptor-related emission in the ZB NWs can be almost completely removed by etching away the impurity-contaminated sidewall grown via a vapour-solid mechanism. The resulting NWs exhibit a long radiative lifetime and a high PL efficiency up to room temperature.
More information can be found in the journal Nanotechnology.
About the author
Thuy T T Vu is currently a PhD candidate under the guidance of Dr Jos Haverkort and Prof. Erik Bakkers in the Photonics and Semiconductor Nanophysics Group (PSN) at Eindhoven University of Technology. He is doing research on nanowire optics and nanowire solar cells. This work has been done in collaboration with Philips Innovation Services.