Surprisingly, gallium nitride single crystals grown by High Nitrogen Pressure Solution method at temperature as high as 1750~K show non uniformities in distribution of impurities which suggests still slow bulk diffusion and very high melting temperature of GaN. In this work, GaN single crystals have been annealed at temperature up to 3350~K at pressure up to 9~GPa in order to induce homogeneization of crystal properties by bulk diffusion. For this purpose the crystals with intentional patterns of impurity distribution were used. The crystals before and after annealing were characterized by PL and CL mapping, photochemical etching sensitive to free electron concentration. It was established, that the bulk diffusion starts at temperature as high as 3300~K. It is reflected in uniformization of both optical and electrical properties of the crystals. This estimation suggests then melting temperature of GaN is significantly higher than current belief [1]. \\[4pt] [1] W.~Utsumi et al. Nature Materials \textbf{2}, 735 (2003).
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Authors
B. Sadovyi
Institute of High Pressure Physics PAS, Sokolowska str., 29/37, 01-142 Warsaw, Poland
I. Grzegory
Institute of High Pressure Physics PAS, Sokolowska str., 29/37, 01-142 Warsaw, Poland
J. Weyher
Institute of High Pressure Physics PAS, Sokolowska str., 29/37, 01-142 Warsaw, Poland
I. Dziecielewski
Institute of High Pressure Physics PAS, Sokolowska str., 29/37, 01-142 Warsaw, Poland
A. Khachapuridze
Institute of High Pressure Physics PAS, Sokolowska str., 29/37, 01-142 Warsaw, Poland
S. Porowski
Institute of High Pressure Physics PAS, Sokolowska str., 29/37, 01-142 Warsaw, Poland
I. Petrusha
V. N. Bakul Inst. for Superhard Materials NASU, Avtozavodska str., 2, Kyiv, 04074 UA
V. N. Bakul Inst. for Superhard Materials NASU, Avtozavodska str., 2, Kyiv, 04074, Ukrain
Dep. of Synthesis and Sintering of Superhard Materials, V. N. Bakul Institute for Superhard Materials NAS Ukraine, Avtozavodska str., 2, Kyiv, 04074
V. Turkevich
V. N. Bakul Inst. for Superhard Materials NASU, Avtozavodska str., 2, Kyiv, 04074, Ukrain
Dep. of Synthesis and Sintering of Superhard Materials, V. N. Bakul Institute for Superhard Materials NAS Ukraine, Avtozavodska str., 2, Kyiv, 04074
I. Petrusha
V. N. Bakul Inst. for Superhard Materials NASU, Avtozavodska str., 2, Kyiv, 04074 UA
V. N. Bakul Inst. for Superhard Materials NASU, Avtozavodska str., 2, Kyiv, 04074, Ukrain
Dep. of Synthesis and Sintering of Superhard Materials, V. N. Bakul Institute for Superhard Materials NAS Ukraine, Avtozavodska str., 2, Kyiv, 04074
V. Kapustianyk
Dep. of Phys., I. Franko National Univ. of Lviv, Dragomanova str., 50, Lviv UA 79005
M. Albrecht
Leibniz Inst. for Crystal Growth, Max-Born-Stra{\ss}e 2, 12489 Berlin, Germany
