Complete composition tunability of InGaN
nanowires using a combinatorial approach
TEVYE KUYKENDALL1, PHILIPP ULRICH1, SHAUL ALONI2AND PEIDONG YANG1,2*
1Department of Chemistry, University of California, Berkeley, California 94720, USA
2Molecular Foundry, Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
Published online: 28 October 2007; doi:10.1038/nmat2037
The III nitrides have been intensely studied in recent years
because of their huge potential for everything from high-
efficiency solid-state lighting and photovoltaics to high-power
and temperature electronics1–3. In particular, the InGaN ternary
alloy is of interest for solid-state lighting and photovoltaics
because of the ability to tune the direct bandgap of this
material from the near-ultraviolet to the near-infrared region.
In an effort to synthesize InGaN nitride, researchers have
tried many growth techniques4–13. Nonetheless, there remains
considerable difficulty in making high-quality InGaN films
and/or freestanding nanowires with tunability across the entire
range of compositions. Here we report for the first time the
growth of single-crystalline InxGa1−xN nanowires across the
entire compositional range from x = 0 to 1; the nanowires
were synthesized by low-temperature halide chemical vapour
deposition9and were shown to have tunable emission from
the near-ultraviolet to the near-infrared region. We propose
that the exceptional composition tunability is due to the low
to accommodate strain-relaxed growth14, which suppresses
the tendency toward phase separation that plagues the thin-
Although much progress has been made in the synthesis
of high-qualityfilms bymetal–organic
deposition (MOCVD)4–7, molecular beam epitaxy8,14and hydride
vapour-phase epitaxy12,13, all of these methods still must contend
with the lack of native substrates for epitaxy, which leads
to threading dislocations in the InGaN and GaN layers due
to lattice mismatch. On the other hand, the unique growth
mechanism of nanowires15has been shown to all but eliminate
threading dislocations, which usually act as non-radiative
recombination centres16,17. This may be essential for overcoming
the so-called ‘valley of death’ drop-off in PL efficiency for
high-In-concentration samples18,19. Although some progress has
been made in incorporating indium into gallium nitride nanowires
using MOCVD, this has been primarily in the form of thin-film
cladding of GaN wires20or the introduction of quantum wells
within GaN wires21. Hydride vapour-phase epitaxy has been
shown to be one of the most promising methods for making
InxGa1−xN nanowires so far22; however, this method has been
limited to a maximum indium incorporation of x = 0.2 owing
to the excess hydrogen evolved as a product of the reaction of
HCl with the metal In and Ga precursors. Hydrogen is well
known to affect the indium incorporation in InGaN alloys23,24.
Another issue for most growth methods is the difficulty of nitrogen
incorporation, particularly for In-rich nitride alloys, which has
led to the need for increasingly high ammonia flow rates. In the
low-temperature halide chemical vapour deposition approach
reported here, drop-off in PL efficiency for high-In-concentration
samples seems to be minimal, excess hydrogen is limited to that
introduced by ammonia and a relatively low V–III ratio is found to
be necessary. In addition, the use of chloride precursors eliminates
the issue of carbon contamination encountered for MOCVD.
The synthesis was carried out using a simple, yet effective,
reactor design shown in Fig. 1. Four temperature zones were
created using a horizontal, single-zone tube furnace and two
independently controlled heating elements. InCl3, GaCl3and NH3
were used as the In, Ga and N sources respectively. Nitrogen carrier
gas was used to transport the InCl3and GaCl3precursors separately
through two of the inner tubes, whereas NH3was carried through
the third inner tube and allowed to mix at the position of the
substrate shown on the right. The synthesis requires no catalyst and
can be carried out on a variety of substrates. Thin Si or sapphire
substrate strips were placed perpendicular to the outlets, along
isothermal lines, such that the composition and corresponding
properties of the nanowires were a result of the precursor-mixing
gradient. Although a temperature gradient of ∼50◦C was present
over the range covered by the substrates, little difference in wire
morphology and/or other properties was observed as a result. The
composition gradient was sharp close to the outlets and tended to
spread with increasing distance downstream of the outlets.
On cooling, the substrates were observed to have a matte finish
and a variety of colours ranging from clear to light yellow on the
GaN side to reddish-black on the InN side (Fig. 1, inset). Figure 2a
(sample 1–13) shows scanning electron microscopy (SEM, see
also Supplementary Information, Fig. S1) images of the nanowires
grown on a silicon substrate from GaN (Fig. 2a, sample 1) to InN
(Fig. 2a, sample 13). Towards the Ga-rich side, the nanowires are
respectively. The wires grow more sharply tapered, with a widening
base, at an indium concentration between 70 and 90%, and to
a larger, less tapered, morphology between 90 and 100%. The
indium-rich wires have diameters and lengths of 100–250nm and
Figure 2b shows X-ray diffraction (XRD) patterns of wires at
several positions (samples 1–13) along the compositional gradient.
The XRD patterns indicate that the wires have the wurtzite crystal
structure. The peaks correspond to the (100), (002) and (101)
planes from left to right, and the plots are ordered with increasing
indium concentration from 1 to 13. The absence of multiple sets of
nature materials VOL 6 DECEMBER 2007 www.nature.com/naturematerials
© 2007 Nature Publishing Group
Received 15 June 2007; accepted 21 September 2007; published 28 October 2007.
1. Schubert, E. F. & Kim, J. K. Solid-state light sources getting smart. Science 308, 1274–1278 (2005).
2. Wu, J. et al. Superior radiation resistance of In1−xGaxN alloys: Full-solar-spectrum photovoltaic
material system. J. Appl. Phys. 94, 6477–6482 (2003).
3. Kung, P. & Razeghi, M. III-Nitride wide bandgap semiconductors: A survey of the current status and
future trends of the material and device technology. Opto-Electron. Rev. 8, 201–239 (2000).
4. Schenk, H. P. D. et al. Indium incorporation above 800◦C during metalorganic vapor phase epitaxy
of InGaN. Appl. Phys. Lett. 75, 2587–2589 (1999).
5. Shan, W. et al. Optical properties of InxGa1−xN alloys grown by metalorganic chemical vapor
deposition. J. Appl. Phys. 84, 4452–4458 (1998).
6. Shimizu, M., Hiramatsu, K. & Sawaki, N. Metalorganic vapor phase epitaxy growth of
(InxGa1−xN/GaN)n layered structures and reduction of indium droplets. J. Cryst. Growth 145,
7. Yoshimoto, N., Matsuoka, T., Sasaki, T. & Katsui, A. Photoluminescence of indium gallium nitride
films grown at high temperature by metalorganic vapor phase epitaxy. Appl. Phys. Lett. 59,
8. Wu, J. et al. Small band gap bowing in In1−xGaxN alloys. Appl. Phys. Lett. 80, 4741–4743 (2002).
9. Takahashi, N., Matsumoto, R., Koukitu, A. & Seki, H. Vapor-phase epitaxy of InxGa1−xN using
chloride sources. J. Cryst. Growth 189–190, 37–41 (1998).
10. Davydov, V. Y. et al. Band gap of hexagonal InN and InGaN alloys. Phys. Status Solidi B 234,
11. Morkoc, H. Nitride Semiconductors and Devices (Springer, Berlin, 1999).
12. Perkins, N. R. et al. Growth of thick GaN films by halide vapor phase epitaxy. Proc. Electrochem. Soc.
96-5, 336–341 (1996).
13. Lu, D. et al. Dynamic scaling of the growth process of GaN thin films deposited on sapphire
substrates by HVPE. Phys. Lett. A 327, 78–82 (2004).
14. Liliental-Weber, Z. et al. Compositional modulation in InxGa1−xN: TEM and X-ray studies. J. Electron
Microscopy 54, 243–250 (2005).
15. Kuykendall, T. et al. Crystallographic alignment of high-density gallium nitride nanowire arrays.
Nature Mater. 3, 524–528 (2004).
16. Sun, Y., Cho, Y.-H., Kim, H.-M. & Kang, T. W. High efficiency and brightness of blue light
emission from dislocation-free InGaN/GaN quantum well nanorod arrays. Appl. Phys. Lett. 87,
17. Ertekin, E., Greaney, P. A., Chrzan, D. C. & Sands, T. D. Equilibrium limits of coherency in strained
nanowire heterostructures. J. Appl. Phys. 97, 114325 (2005).
18. Fuhrmann, D. et al. Optimization scheme for the quantum efficiency of GaInN-based green
light-emitting diodes. Appl. Phys. Lett. 88, 071105 (2006).
19. Fuhrmann, D. et al. Optimizing the internal quantum efficiency of GaInN SQW structures for green
light emitters. Phys. Status Solidi C 3, 1966–1969 (2006).
20. Qian, F., Gradecak, S., Li, Y., Wen, C.-Y. & Lieber, C. M. Core/Multishell nanowire heterostructures as
multicolor, high-efficiency light-emitting diodes. Nano Lett. 5, 2287–2291 (2005).
21. Kim, H.-M. et al. High-brightness light emitting diodes using dislocation-free indium gallium
nitride/gallium nitride multiquantum-well nanorod arrays. Nano Lett. 4, 1059–1062 (2004).
22. Kim, H.-M. et al. Formation of InGaN nanorods with indium mole fractions by hydride vapor phase
epitaxy. Phys. Status Solidi B 241, 2802–2805 (2004).
23. Kumagai, Y., Takemoto, K., Hasegawa, T., Koukitu, A. & Seki, H. Thermodynamics on tri-halide
vapor-phase epitaxy of GaN and InxGa1−xN using GaCl3and InCl3. J. Cryst. Growth 231,
24. Scholz, F. et al. Low pressure MOVPE of GaN and GaInN/GaN heterostructures. J. Cryst. Growth 170,
25. Doppalapudi, D., Basu, S. N., Ludwig, K. F. Jr & Moustakas, T. D. Phase separation and ordering in
InGaN alloys grown by molecular beam epitaxy. J. Appl. Phys. 84, 1389–1395 (1998).
26. Yang, B. et al. Structural and optical properties of GaN layers directly grown on 6H-SiC(0001) by
plasma-assisted molecular beam epitaxy. Mater. Sci. Forum 264–268, 1235–1238 (1998).
27. Snyder, R. L., Fiala, J. & Bunge, H. J. (eds) Defect and Microstructure Analysis by Diffraction (Int.
Union Crystallogr. Monogr. Crystallogr., Vol. 10, Oxford Univ. Press, Oxford, 1999).
28. Mattila, T. & Zunger, A. Predicted bond length variation in wurtzite and zinc-blende InGaN and
AlGaN alloys. J. Appl. Phys. 85, 160–167 (1999).
29. Ho, I. H. & Stringfellow, G. B. Solid phase immiscibility in GaInN. Appl. Phys. Lett. 69,
30. Caetano, C., Teles, L. K., Marques, M., Dal Pino, A. Jr & Ferreira, L. G. Phase stability, chemical
bonds, and gap bowing of InxGa1−xN alloys: Comparison between cubic and wurtzite structures.
Phys. Rev. B 74, 045215 (2006).
31. Liliental-Weber, Z. et al. Relaxation of InGaN thin layers observed by X-ray and transmission electron
microscopy studies. J. Electron. Mater. 30, 439–444 (2001).
32. Stach, E. A. et al. Watching GaN nanowires grow. Nano Lett. 3, 867–869 (2003).
33. Waltereit, P. et al. Nitride semiconductors free of electrostatic fields for efficient white light-emitting
diodes. Nature 406, 865–868 (2000).
34. Shubina, T. V. et al. Mie resonances, infrared emission, and the band gap of InN. Phys. Rev. Lett. 92,
35. Wu, J. et al. Effects of the narrow band gap on the properties of InN. Phys. Rev. B 66, 201403 (2002).
This work was supported in part by the US Department of Energy and DARPA-UPR. Work at the
Lawrence Berkeley National Laboratory was supported by the Office of Science, Basic Energy Sciences,
Division of Materials Science of the US Department of Energy. We thank T. Umbach, P. Pauzauskie
and S.-Y. Bae for discussion, and the National Center for Electron Microscopy for the use of
Correspondence and requests for materials should be addressed to P.Y.
Supplementary Information accompanies this paper on www.nature.com/naturematerials.
Reprints and permission information is available online at http://npg.nature.com/reprintsandpermissions/
nature materials VOL 6 DECEMBER 2007 www.nature.com/naturematerials
© 2007 Nature Publishing Group