Local Structure around In Atoms in InxGa1-xN Single-Quantum-Well by XAFS

T. MiyanagaDepartment 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 studyInGaN 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)X-raySampleSSDStructure 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)X-raySampleSSDRotated

XAS of In0.20Ga0.80N SQW

EXAFS kc(k) spectra and Fourier transform of In K-edge for In0.20Ga0.80N SQW in horizontal and vertical directions.In-NIn-Ga/In

wurtzite structure (GaN, InN)

InNGa or InAssumption: InGaN SQW is wurtzite

Theoretical fitting for In K-edge for In0.20Ga0.80N SQW in horizontal direction for 1st and 2nd peaks.

Structural parameters obtained from EXAFS analyses for second peak in FT.

*Sum of N for In-Ga and In-In is fixed to 12

Result 1Interatomic 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

Result 2(1) Horizontal: In atoms are randomly distributed(2) Vertical: In atoms are aggregated and located top and bottomIn mole fluctuation !

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)

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