epitaxial lateral overgrowth of aln layers on patterned sapphire substrates
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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. Outline. Introduction Experiments Results and discussion Conclusion References. Introduction.

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epitaxial lateral overgrowth of aln layers on patterned sapphire substrates

Epitaxial lateral overgrowth of AlN layerson patterned sapphire substrates

指導教授: 管 鴻 教授

學 生: 林耀祥

日 期:97.12.01

outline
Outline
  • Introduction
  • Experiments
  • Results and discussion
  • Conclusion
  • References
introduction
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 high-quality 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
experiments
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 high-temperature MOVPE technique under H2 atmosphere.
slide5
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.
results and discussion
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.

slide7
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,
slide8
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.

slide9
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.
conclusion
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.
references
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 30p-L-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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