GaN-based semiconductors have already begun to be used even for power devices or electronic devices including high frequency devices. In order to apply the GaN based semiconductors to these applications, high quality GaN single crystal substrates has been needed more than ever before. Although the crystals with the dislocation density of about 10⁶ cm^-2 and the size of 2 inch has been required so far, the size of more than 3 inch and dislocation density of less than 10⁵ cm^-2 begun to be needed. The hydride vapor phase epitaxy (HVPE) method has a lead in the growth of GaN single crystal substrate because of an advantage of high growth rate of GaN single crystals. However, further decrease in the dislocation density is difficult in the HVPE method. Although the Na flux method enables us to grow low dislocation density GaN single crystals {1-3] (shown in Figure1), low growth rate has been pointed out as a problem to be solved.

Figure 1. 2 inch GaN single crystal substrate grown by the Na flux-LPE method.

We tried to increase the growth rate by applying the thermal convection to the Na flux method. The setup for applying the thermal convection to the Na flux LPE method is shown in Figure 2.

Figure 2. Experimenta setup for the LPE growth under the thermal convection.

As a result, growth rate could be increased nearly three-fold as compared to the case without thermal convection as shown in Figure 3. In the Na flux method, supersaturation is generated by dissolution of pressurized nitrogen gas. By this effort, growth rate of about 30 um/h could be achieved in the Na flux method for the first time. The result mentioned above indicates that dissolution of the nitrogen gas is limited by the diffusion.

Figure 3. The effect of thermal convection on the growth rate of Na flux-LPE method.

Another advantage of the convection is that the high nitrogen concentration in the solution can be easily attained, which can suppress the nucleation of GaN on the crucible near gas-liquid interface. High rate growth without heterogeneous nucleation was used to obtin the 2 inch GaN single crystal with the thickness of over 3 mm. Current message is that the Na flux method is also effective for the growth of non-polar GaN substrate. Although non-polar GaN thin film could already be grown by the metal organic chemical vapor deposition (MOCVD) method, crystallinity was poor. We tried the LPE growth on the non-polar thin film with poor crystallinity [4,5]. As a result, crystalline quality could be drastically improved from several thousands arcsec to about 200 arcsec in both m- and a-face GaN substrate.

References

[1] H.Yamane, M.Shimada et.al., Chem.Mater., 9 (1997) 413.

[2] F. Kawamura, M. Morishita, K. Omae, M. Yoshimura, Y. Mori, and T. Ssasaki, J. Mater. Sci.: Mater. Electron, 16 (2005) 29-34.

[3] F. Kawamura, H. Umeda, M. Morishita, M. Kawahara, M. Yoshimura, Y. Mori, T. Sasaki and Y. Kitaoka, Jpn. J. Appl. Phys., 45, 43 (2006) L1136

[4] T. Iwahashi, Y. Kitaoka, M. Kawahara, F. Kawamura, M. Yoshimura, Y. Mori, T. Sasaki, R. Armitage and H. Hirayama, Jpn. J. Appl. Phys., 46, 4 (2007) L103

[5] T. Iwahashi, Y. Kitaoka, F. Kawamura, M. Yoshimura, Y Mori, T. Sasaki, R. Armitage and H. Hirayama, Jpn. J. Appl. Phys., 46, 10 (2007) L227

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/10583 must be provided.

1. Polymorphism control of pharmaceutical compound acetaminophen by ultrasonic irradiation
2. Improvement of femtosecond laser-induced nucleation technique for proteins: Studies of effect of gel-solution interface
3. Fabrication of bulk GaN crystals by Na flux method with a necking technique and a coalescence growth
4. The optimization of solution flow rate producing high-quality and large protein crystals
5. First-principles calculation of the carbon-added Na-flux GaN growth on GaN(0001)
6. Impurity control of CsLiB₆O₁₀ for improving UV-induced damage tolerance