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Epitaxial lateral overgrowth of
AlN layers
on patterned sapphire substrates
指導教授: 管 鴻 教授
學
生: 林耀祥
日
期：97.12.01
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Outline
• Introduction
• Experiments
• Results and discussion
• Conclusion
• References
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Introduction
• The realization of high-performance UV light-emitting
devices is one of the most important targets for group III
nitride semiconductors.
• To realize high-performance UV devices such as light
emitting diodes . the growth of high-quality AlN is
essential. It is still a critical issue to obtain highquality AlN .
• A combination of high-temperaturegrowth and ELO will lead to
the reduction of threading dislocation density and thus
achieve to much higher quality AlN
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Experiments
• Two different directions of pattrned sapphire substrates (0001)
have been used in this investigation. In the first type of
substrate, linear trenches have been formed along the (1010)
direction. In the secondtype, trenches have been formed along
the (1120) direction. The width and depth of the trenches are
both 500 nm. The adjacent terrace width is 3 μm.
• The ELO-AlN layers were grown on these substrates by hightemperature MOVPE technique under H2 atmosphere.
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• The growth is carried out at a constant pressure of 100 Torr
• the substrate is annealed at a temperature of 1330 °C for 5
minutes.
• the growth is carried out at a temperature of 1300 °C, for 7
120 minutes.
• For comparison, the growth of AlN at a relatively low
temperature of 1100 °C on a trench pattern along (1120)
direction was also performed.
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Results and discussion
• Figure 2 shows a SEM cross-sectional image of AlN grown at a
temperature of 1100 °C, which is the temperature commonly
used for the growth of AlN on sapphire. Although AlN was
coalesced, the surfaceis quite rough. In comparison, the
surface of AlN grown at temperatures higher than 1300 °C is
atomically flat.
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• Figure 3 shows the SEM cross-section image of the AlN layer
grown on the sapphire substrate with grooves formed along
(1010) direction. As clearly seen in the SEM image, AlN
layer was not coalesced. There is a gap between the adjacent
layers. analyze the dislocations in the layersespecially in
the regions between the vertical portions,
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• Figure 4 shows the TEM image of portion surrounded by black
dotted lines in the Fig. 3. Dislocations are found
to propagate vertically from the seed region through the top
surface. From these observations, it can be concluded that
the grooves formed on sapphire substrates along the (1010)
direction is not suitable for growing AlN layers with
reduced dislocation density.
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• The SEM image of the cross-section of the AlN layers grown
on the sapphire substrates with the linear grooves formed
along the (1120) direction is presented in Fig. 5. As seen
in the SEM image. TEM analysis was done on a prominent
portion of the AlN layer indicated by the white dotted lines
in order to analyze the dislocation propagation behaviour in
detail. substrates.
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Conclusion
• High temperature MOVPE growth of AlN on the sapphire
substrate having trench pattern was conducted.
• We found a strong difference of the property of ELO between
two trench directions. In order to obtain coalesced AlN,
(1120) trench is essential. The average dislocation density
of a coalesced AlN was 6.7 × 108 cm–2, which is less than a
half that of AlN grown on planer sapphire.
• (1120) trench (0002) XRD rocking curve FWHM 314 aresec is
better than (1010) 352 aresec. These results show that ELO
technique is also suitable for reducing dislocation density
of AlN on sapphire.
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References
• [1] S. Nitta, M. Kariya, T. Kashima, S. Yamaguchi, H. Amano,
and I. Akasaki, Appl. Surf. Sci. 159/160, 421 (2000).
• [2] N. Fujimoto, T. Kitano, G. Narita, T. Fuse, K.
Balakrishnan, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, K.
• Shimono, T. Noro, T. Takagai, and A. Bandoh, 52nd JSAP 30pL-9 (2005).
• [3] M. Imura, K. Nakano, T. Kitano, T. Fuse, N. Fujimoto, K.
Balakrishnan, M. Iwaya, S. Kamiyama, H. Amano, T.Noro, and T.
Takagi, 52nd JSAP 30p-L-10 (2005).
• [4] T. M. Katona, M. D. Craven, J. S. Speck, and S. P.
DenBaars, Appl. Phys. Lett. 85, 1350 (2004).
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