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Professor Zbigniew R. Zytkiewicz, Institute of Physics, Polish Academy of Sciences

Event Date: 
Monday, June 18, 2018 - 3:30pm to 4:30pm

Self-assembled formation of GaN nanowires by molecular beam epitaxy: in-situ monitoring of the growth mechanisms, properties and applications.

M. Sobanska, Z.R. Zytkiewicz, A. Wierzbicka, K. Klosek and G. Tchutchulashvili

Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland

It is well established that GaN nanowires (NWs) are promising building-blocks of new electronic and optoelectronic devices. Much effort is recently concentrated on controlled growth of GaN NWs on non-crystalline substrates, which offers a large degree of freedom in designing new devices. However, due to the lack of fundamental growth studies, the growth mechanisms underlying the formation of GaN NWs on non-crystalline substrates are still not well understood, hindering the control of the growth process. In this talk we will discuss the mechanisms of spontaneous nucleation and growth of GaN NWs on amorphous AlxOy buffer layers by molecular beam epitaxy (MBE) [1], and compare them with analogous processes occurring on nitridated Si – the substrate commonly used for MBE growth of GaN NWs. In this way, a general understanding of the formation of GaN NWs is sought, with particular emphasis on the role of the substrate and its influence on the growth process. To this end, a reflection high-energy electron diffraction RHEED [2, 3] and a line-of-sight quadrupole mass spectrometry QMS [4] were used for in-situ monitoring of all stages of NW growth on both substrates. The experimental results are correlated with studied ex-situ morphology of the samples with different growth durations, which allowed to distinguish three stages of nanowires’ evolution: (i) an incubation preceding the formation of GaN islands, (ii) nucleation and transformation of GaN islands into the NW shape and (iii) their further anisotropic growth. Characteristic physical processes for each stage are determined and analyzed. In this way, comprehensive analysis of microscopic mechanisms of nucleation and growth of GaN nanowires on both substrates is presented. Then we show that under proper growth conditions, GaN NWs with excellent structural and optical properties, as observed by SEM, TEM, XRD [5, 6] and PL [2, 7] techniques can be formed on a-AlxOy buffers. In this way, our results pave the way to the crystallization of high quality GaN NWs on any substrate, provided it is compatible with the MBE technology and its surface is covered by a thin a-AlxOy buffer layer.

[1] M. Sobanska et al., J. Appl. Phys., 115, 043517 (2014),

[2] M. Sobanska et al., J. Appl. Phys., 118, 184303 (2015),

[3] M. Sobanska et al., Cryst. Growth Des., 16, 7205–7211 (2016),

[4] M. Sobanska et al., Nanotechnology, 27, 325601 (2016).

[5] A. Wierzbicka et al. Nanotechnology, 24, 035703 (2013),

[6] J. Borysiuk et al., Nanotechnology, 25, 135610 (20140,

[7] K.P. Korona et al. J. Luminescence, 155, 293 (2014).

Financial support from the NCN grants 2016/21/N/ST3/03381 and 2016/23/B/ST7/03745 is acknowledged.

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