Download LOCAL STRUCTURE AROUND In ATOMS IN InxGa1

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)