Berlin 2008 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

HL: Fachverband Halbleiterphysik

HL 44: Quantum dots and wires: preparation and characterization II

HL 44.3: Vortrag

Donnerstag, 28. Februar 2008, 17:15–17:30, EW 201

Catalyst-free and catalyst-induced growth of GaN nanowires by molecular beam epitaxy — •Caroline Chèze¹, Lutz Geelhaar¹, Walter Weber¹, Henning Riechert¹, Philomela Komninou², Thomas Kehagias², and Theodoros Karakostas² — ¹Qimonda and NaMLaB, Dresden, Germany — ²Aristotle University of Thessaloniki, Thessaloniki, Greece

GaN nanowires (NWs) were grown by molecular beam epitaxy with and without catalyst under very similar conditions, enabling a direct comparison of their growth mechanisms. The type of substrate determines whether a catalyst is necessary to induce the formation of NWs. On sapphire, NWs grow only when Ni seeds are deposited on the substrate before GaN-growth. Particles found at the NW-tips suggest that NWs form in a way similar to the vapour-liquid-solid mechanism. In contrast, on Si NWs form in a self-induced way without any catalyst. To elucidate the growth mechanisms, the incorporation rate of Ga was monitored in situ by line-of-sight quadrupole mass spectrometry. In all cases, growth starts with a reduced incorporation rate, i.e. nucleation is delayed. However, the growth rate saturates after different delays for the two different ways of NW-formation. At a growth temperature of 780°C, the nucleation phase is on Si at least five times longer than on sapphire (>3000 s vs. about 600 s). Thus, the external catalyst Ni strongly facilitates the formation of NWs. Based on these observations, we will discuss the possible growth mechanisms leading to the formation of NWs either by the catalyst-free (on Si) or by the catalyst-induced (on sapphire) approach.