There are some promising methods for obtaining good quality GaN crystals i.e. growth from the vapor phase, called HVPE¹ or crystallization from a solution: growth in gallium/sodium solution, the sodium flux method², or in supercritical ammonia, the ammonothermal method³. It is also well known that the High Nitrogen Pressure Solution (HNPS) growth allows obtaining high quality GaN crystals⁴. Recently, the multi-feed-seed (MFS) configuration in the HNPS growth method has been proposed and developed⁵. This configuration has been based on the conversion of free-standing HVPE-GaN crystals to the free-standing, pressure grown HNPS-GaN of much higher quality than the seeds. It has been already shown that the crystallization of GaN in the MFS configuration without an intentional doping results in growth of strongly n-type crystals with free electron concentration increasing with growth temperature. It has been suggested that so high free electron concentration in HNPS-MFS-GaN can be associated with high oxygen concentration in the material. Obviously, the oxygen impurities in the GaN crystals can be compensated by magnesium. The HNPS-MFS-GaN:Mg crystallization has been already reported⁶. Highly resistive crystals have been obtained. However, one big difference in crystal growth procedure has been noted. The crystallization process has proceeded on the (000-1) GaN surface instead of the (0001) surface, typical for n-type GaN growth. It can be thus suggested that polarity of the GaN seed surface is determined and controlled by the Ga solution and its impurities.

In this paper the role and influence of impurities such as oxygen, indium and magnesium on GaN crystal growth from liquid solution in the MFS configuration will be presented and discussed in details. The differences in the properties of differently doped GaN crystals will be shown. It will be also demonstrated that HNPS-MFS-GaN crystals can be successfully used as substrates for epitaxy of optoelectronic and electronic devices.

[1] K. Motoki, SEI Technical Review, Number 70, April 2010; 28

[2] Y. Mori, M. Imade. K. Murakami, H. Takazawa, H. Imabayashi, Y. Todoroki, K. Kikamoto, M. Maruyama, M. Yoshimura, Y. Kitaoka, T. Sasaki, Journal of Crystal Growth, 350 (1), 72-74, (2012)

[3] R. Doradziński, R. Dwilinski, J. Garczynski, L.P. Sierzputowski, Y. Kanbara, in Technology of Gallium Nitride Crystal Growth, edited by D.Ehrentraut, E. Meissner, and M. Boćkowski, (Springer-Verlag, Heidelberg, ISBN 978-3-642-04828-9), 137-158, (2010)

[4] M. Bockowski, P. Strak, I. Grzegory, S. Porowski, in Technology of Gallium Nitride Crystal Growth, ed. by D. Ehrentraut, E. Meissner, M. Bockowski, (Springer-Verlag, Heidelberg, ISBN 978-3-642-04828-9), 207-220 (2010)

[5] M. Bockowski, I. Grzegory, B. Łucznik, T. Sochacki, G. Nowak, B. Sadovyi, P, Strak, G. Kamler, E. Litwin-Staszewska, S. Porowski, Journal of Crystal Growth 350 (1), 5-10 (2012)

[6] I. Grzegory, M. Bockowski, B. Lucznik, J. L. Weyher, E. Litwin-Staszewska, L. Konczewicz, B. Sadovyi, P. Nowakowski, S. Porowski. Journal of Crystal Growth 350 (1), 50–55 (2012)

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1. Homoepitaxial HVPE-GaN growth on non-polar and semi-polar seeds
2. Preparation of free-standing GaN substrates from thick GaN layers crystallized by Hydride Vapor Phase Epitaxy on ammonothermally grown GaN seeds
3. Homoepitaxial HVPE-GaN growth on non-polar and semi-polar seeds
4. Preparation of free-standing GaN substrates from thick GaN layers crystallized by Hydride Vapor Phase Epitaxy on ammonothermally grown GaN seeds
5. Measurements of strain in AlGaN/GaN HEMT structures grown by plasma assisted molecular beam epitaxy
6. Carrier recombination under one-photon and two-photon excitation in GaN epilayers
7. Recognition of chemical (electrically active) non-homogeneities in thick HVPE-grown GaN layers
8. Mass flow and reaction analysis of the growth of GaN layers by HVPE
9. Bowing of epitaxial structures grown on bulk GaN substrates
10. Diffusion and diffusion induced defects in GaN
11. Magnetotransport studies of Ga(Mn,Fe)N bulk crystals