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Local Structure around In Atoms in InxGa1-xN SingleQuantum-Well by XAFS T. Miyanaga Department of Materials Science and Technology, Faculty of Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan InGaN LED Band gap and In concentration x Chichibu, S.F., Sota, T., Wada, K., Brandt, O., Ploog, K.H., DenBaars, S.P., and Nakamura, S., Phys. Stat. Sol.(a), 183, 91 (2001). Purpose of the study InGaN SQW shows high quantum efficiency, although it has very high densities of threading dislocations. In mole fluctuation in InGaN active layers is proposed as its origin. To make the emission mechanism clear in InGaN LED, it is important to clarify local structures around In atoms. Fluorescence EXAFS is applied to study the InGaN SQW. Experimental Samples: The sample was grown by MOCVD 3nm SQW InxGa1-xN (x = 0.145 blue, 0.20 green, 0.275 amber) Sample SSD X-ray Structure of InGaN SQW (3nm) X-ray absorbing measurements SPring-8: BL01B1, BL38B1, BL10XU -In K-edge (27.9keV) -Si (111) Monochromator -Fluorescence EXAFS -19-SSD(Ge) (3nm SQW, Cap layers) SSD Sample X-ray Rotated XAS of In0.20Ga0.80N SQW 0.7 μt 0.6 0.5 0.4 Horizontal 0.3 27.6 27.8 28 28.2 E / keV 28.4 28.6 0.08 μt 0.07 0.06 0.05 Vertical 0.04 27.6 27.8 28 28.2 E / keV 28.4 28.6 Horizontal Vertical kχ(k) /Å-1 0.2 0.1 0 -0.1 -0.2 |FT(r)| / arb.unit EXAFS kc(k) spectra and Fourier transform of In K-edge for In0.20Ga0.80N SQW in horizontal and vertical directions. 0.1 -1 k/Å 10 In-N In-Ga/In 0.05 0 5 Horizontal Vertical 0 2 4 r/ Å 6 8 wurtzite structure (GaN, InN) Assumption: InGaN SQW is wurtzite ● In ● N ● Ga or In Theoretical fitting for In K-edge for In0.20Ga0.80N SQW in horizontal direction for 1st and 2nd peaks. Exp. Fit (In-N) Fit (In-Ga/In) |FT(r)| / arb.unit 0.1 0.05 0 0 2 4 r/Å 6 8 Structural parameters obtained from EXAFS analyses for second peak in FT. *Sum of N for In-Ga and In-In is fixed to 12 In-Ga x 0.145 0.20 0.275 In-In h/v r/A N* s/A r/A N* s/A h 3.23 10.2 0.066 3.23 1.8 0.041 v 3.25 9.3 0.080 3.32 2.7 0.099 h 3.22 9.7 0.077 3.24 2.3 0.067 v 3.26 7.7 0.064 3.28 4.3 0.083 h 3.23 9.1 0.071 3.25 2.9 0.082 v 3.26 8.7 0.075 3.30 3.3 0.081 Result 1 Interatomic distance (1) In-N: Horizontal ~ Vertical (2.10A) (2) In-Ga/In: Vertical (3.28-30A) > Horizontal (3.24-25A) SQW is biaxially compressed in a-b plane The ratio of coordination number y = NIn-In / (NIn-In + NIn-Ga) from EXAFS x : average concentration of In 0.4 Vertical 0.35 y 0.3 0.25 0.2 0.15 0.1 0.1 Horizontal 0.15 0.2 x 0.25 0.3 Result 2 (1) Horizontal: In atoms are randomly distributed (2) Vertical: In atoms are aggregated and located top and bottom In mole fluctuation ! Conclusion EXAFS result is evidence of composition fluctuation of In atom in the SQW and should closely related to the high quantum efficiency of InGaN LED Co-authors T. Azuhata, S. Matsuda, Y. Ishikawa (Hirosaki University, Japan) T. Uruga, H. Tanida (SPring-8, JASRI, Japan) SF. Chichibu (University of Tsukuba, Japan) T. Sota (Waseda University, Japan) T. Mukai (Nichia Corporation, Japan)