In this thesis, we have investigated the structural and optical properties of self-organized disk-like GaN dots grown on Al0.11Ga0.89N/sapphire by metal organic chemical vapor deposition (MOCVD) by means of atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy. AFM studies show that for GaN coverage of 1.8 and 5.5 MLs, no island formation was observed. As the GaN coverage was increased above 7.3 MLs, self-organized GaN dots started to form, which is a typical characteristic of the Stranski-Krastanow (S-K) growth mode. And the wetting layer (WL) thickness is estimated to be about 7.2 MLs from the dependence of the dot density on the GaN coverage. The disk-like dot size varies with the GaN coverage, which was estimated from the TMGa flow rate. We knew that average height was about 5.7 to 8.2 nm and the standard deviation was about 2.1 to 2.8 nm from the histograms of dot height distribution with different GaN coverage. The average diameter was about 175 to 215 nm. The linear increasing of dot size with the increasing of the GaN coverage was observed. The estimated dot density is about 9.1x108, 1.1x109, 7.2x108/cm2 for the GaN coverage of 9.1, 10.9, 13.6 MLs, respectively. When the GaN coverage exceeded 13.6 MLs, the decrease in dot density is attributed to the coalescence of dots. From the morphologies observation of single disk-like GaN dot, we can classify the shape of single disk-like dot into symmetric and irregular types, where the symmetric type is divided into the lens-like and ellipse-like types. We consider that the ellipse-like GaN dot is likely made up of two smaller dots which was evidenced from the profile of the morphology.
We observed that the peak energy of the disk-like GaN dots increase with the decreasing GaN coverage from the PL measurement. It has been found that the disk-like
temperature. The increasing of the transition energy with decreasing dot size is ascribed to the quantum size effect in the growth direction. Moreover, we observed that the FWHM of the disk-like GaN dots increases as the temperature increases. This is due to the increasing carrier-phonon scattering. It is also found that the increasing of the FWHM with the decreasing GaN coverage is attributed to the increasing size fluctuation.
We have also investigated the temperature dependence of PL properties of self-organized disk-like GaN dots with height ranging from 6.6 to 8.2 nm. The temperature dependence of GaN dots exciton emission and linewidth does not show any typical temperature dependent properties of the Stranski-Krastanow dots. The PL peak energy of the disk-like GaN dots exhibits an initial blue-shift with increasing temperature and then followed by a red-shift which obeys the Vashini’s relation. The strength of blue-shifts increases with dot size. Such an energy shift with increasing temperature is a signature of QDs grown by SK growth mode and has also been observed in other QDs systems except for GaN QDs. This is a typical characteristic of the exciton localization. The localization energy of 5 meV for GaN epilayer is ascribed to the donor-bound exciton. However, the localization energy of 6 to 28 meV for disk-like dots is considered to exciton localization of defect state in the dots. In addition, the temperature dependent PL integrated intensity of GaN dots is analyzed by the Arrhenius equation. We can obtain the activation energies of 43±4, 70±13, and 106±13 meV for 6.6, 7.1, and 8.2 nm dots, respectively. From the PL spectrum of an Al0.11Ga0.89N epilayer, the two peaks are contributed to the NBE and defect-related emissions. We found that the energy difference between Idefect of AlGaN and IQD is close to the obtained activation energy. Finally, we suggest that the activation energy is the required energy of excitons from the QD confined state thermalized into defect states of AlGaN layers.
References
[1] A. J. Fischer, W. Shan, J. J. Song, Y. C. Chang, R. Horning, and B. Goldenberg, Appl.
Phys. Lett. 71, 1981 (1997).
[2] Annamraju Kasi Viswanath, Joo In Lee, Sungkyu Yu, Dongho Kim, Yoonho Choi, and Chang-hee Hong, J. Appl. Phys. 84, 3848 (1998).
[3] Liwu Lu, Hua Yan, C L Yang, Maohai Xie, Zhanguo Wang, J Wang and Weikun Ge, Semicond. Sci. Technol. 17, 957 (2002).
[4] J. Bai, M. Dudley, L. Chen, B. J. Skromme, B. Wagner, R. F. Davis, U. Chowdhury and R. D. Dupuis, J. Appl. Phys. 97, 116101 (2005).
[5] S. Nakamura, M. Senoh, and T. Mukai, Jpn. J. Appl. Phys., Part 2 32, L8 (1993).
[6] S. Nakamura, T. Mukai, and M. Senoh, Appl. Phys. Lett. 64, 1686 (1994).
[7] S. Nakamura and T. Mukai, Jpn. J. Appl. Phys., Part 2 31, L1457 (1992).
[8] S. Nakamura, T. Mukai, M. Senoh, and N. Isawa, Jpn. J. Appl. Phys., Part 2 31, L139 (1992).
[9] S. Nakamura, M. Senoh, S. I. Nagahama, N. Isawa, T. Yamada, T. Matsushita, H.
Kiyoku and Y. Sugimoto, Jpn. J. Appl. Phys., Part 2 35, L74 (1996).
[10] S. Chichibu, T. Azuhata, T. Sota, and S. Nakamura, J. Appl. Phys. 79, 2784 (1996).
[11] Y. Kawakami, Z. G. Peng, Y. Narukawa, S. Fujita, S. Fujita, and S. Nakamura, Appl.
Phys. Lett. 69, 1414 (1996).
[12] S. Chichibu, A. Shikanai, T. Azuhata, T. Sota, A. Kuramata, K. Horino, and S.
Nakamura, Appl. Phys. Lett. 68, 3766 (1996).
[13] A. Shikanai, T. Azuhata, T. Sota, S. Chichibu, A. Kuramata, K. Horino, and S.
Nakamura, J. Appl. Phys. 81, 417 (1997).
[14] S. Nakamura, S. Masayuki, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, Y.
Sugimoto, and K. Hiroyuki, Appl. Phys. Lett. 70, 1417 (1997).
[15] M. A. Khan, J. N. Kuznia, A. R. Bhattarai, and D. T. Olson, Appl. Phys. Lett. 62, 1786 (1993).
[16] M. A. Khan, A. Bhattarai, J. N. Kuznia, and D. T. Olson, Appl. Phys. Lett. 63, 1214 (1993).
[17] M. Razeghi, and A. Rogalski, J. Appl. Phys. 79, 7433 (1996).
[18] Y. Arakawa and H. Sakaki, Appl. Phys. Lett. 40, 939 (1982).
[19] Y. Arakawa, T. Someya, and K. Tachibana, IEICE Trans. Electron. E83-C, 564 (2000).
[20] I. N. Stranski and V. L. Krastanov, Akad. Wiss. Lit. Mainz Abh. Math. Naturwiss.
Kl. 146, 797 (1939).
[21] Wen-Cheng KE, Huai-Ying HUANG, Ching-Shun KU, Kao-Hsi YEN, Ling LEE, Wei-Kuo CHEN, Wu-Ching CHOU, Ming-Chih LEE, Wen-Hsiung CHEN, Wen-Jen LIN, Yi-Cheng CHENG and Ya-Tong CHERNG, Jpn. J. Appl. Phys. 43 L780 (2004).
[22] S. Guha, A. Madhukar, and K. C. Rajkuma, Appl. Phys. Lett. 57, 2110 (1990).
[23] S. Varma, C. M. Reaves, V. Bressler-Hill, S. P. Den Baars, and W. H. Weinberg, Surf. Sci. 393, 24 (1997).
[24] K. Kamath, P. Bhattacharya, T. Sosnowski, T. Norris, and J. Phillips, Electron. Lett.
32, 1374 (1996).
[25] R. Mirin, A. Gossard, and J. Bowers, Electron. Lett. 32, 1732 (1996).
[26] D. Bimberg, N. N. Ledentsov, M. Grundmann, N. Kirstaedter, O. G. Schmidt, M. H.
Mao, V. M. Ustinov, A. Yu Egorov, A. E. Zhukov, P. S. Kopev, Zh. I. Alferov, S. S.
Ruvimov, U. Gösele, and J. Heydenreich, Jpn. J. Appl. Phys., Part 1 35, 1311 (1996).
[27] Q. Xie, A. Kalburge, P. Chen, and A. Madhukar, IEEE Photonics Technol. Lett. 8, 965 (1996).
[28] F. Widmann, B. Daudin, G. Feuillet, Y. Samson, J. L. Rouviere, and N. Pelekanos, J.
Appl. Phys. 83, 7618 (1998).
[29] F. Widmann, J. Simon, B. Daudin, G. Feuillet, J. L. Rouviere, N. T. Pelekanos, and G. Fishman, Phys. Rev. B 58, R15989 (1998).
[30] B. Daudin, F. Widmann, G. Feuillet, Y. Samson, M. Arlery, and J. L. Rouvie`re, Phys. Rev. B 56, R7069 (1997).
[31] Koji Kawasaki, Daisuke Yamazaki, Atsuhiro Kinoshita, Hideki Hirayama, Kazuo Tsutsui and Yoshinobu Aoyagi, Appl. Phys. Lett. 79, 2243 (2001).
[32] M. Miyamura, K. Tachibana, and Y. Arakawa, Appl. Phys. Lett. 80, 3937 (2002).
[33] P. Ramval, S. Tanaka, S. Nomura, P. Riblet, and Y. Aoyagi, Appl. Phys. Lett. 73, 1104 (1998).
[34] P. Ramval, P. Riblet, S. Nomura, Y. Aoyagi, and S. Tanaka, J. Appl. Phys. 87, 3883 (2000).
[35] V. J. Leppert, C. J. Zhang, H. W. H. Lee, I. M. Kennedy, and S. H. Risbud, Appl.
Phys. Lett. 72, 3035 (1998).
[36] E. Borsella, M. A. Garcia, G. Mattei, C. Maurizio, P. Mazzoldi, E. Cattaruzza, F.
Gonella, G. Battagin, A. Quaranta, and F. D'Acapito, J. Appl. Phys. 90, 4467 (2001).
[37] E. Martinez-Guerrero, C. Adelmann, F. Chabuel, J. Simon, N. T.
Pelekanos, G. Mula, B. Daudin, G. Feuillet, and H. Mariette, Appl.
Phys. Lett. 77, 809 (2000).
[38] B. Daudin, G. Feuillet, H. Mariette, G. Mula, N. Pelekanos, E. Molva, J. L.
Rouviere, C. Adelmann, E. Martinez-Guerrero, J. Barjon, F. Chabuel, B. Bataillou, and J. Simon, Jpn. J. Appl. Phys., Part 1 40, 1892 (2001).
[39] A. D. Andreev and E. P. O'Reilly, Phys. Rev. B 62, 15851 (2000).
[40] V. A. Fonoberov, E. P. Pokatilov, and A. A. Balandin, J. Nanosci. Nanotechnol. 3, 253 (2003).
[41] Vladimir A. Fonoberov and Alexander A. Balandin, J. Appl. Phys. 94, 7178 (2003).
[42] D. Leonard, K. Pond, and P. M. Petroff, Phys. Rev. B 50, 11687 (1994).
[43] A. Y. Polyakov, M. Shin, J. A. Freitas, M. Skowronski, D. W. Greve, and R. G.
Wilson, J. Appl. Phys. 80, 6349 (1996).
[44] Z. Y. Xu, Z. D. Lu, X. P. Yang, Z. L. Yuan, B. Z. Zheng, J. Z. Xu, W. K. Ge, Y.
Wang, J. Wang, and L. L. Chang, Phys. Rev. B 54, 11528 (1996).
[45] P. Ramvall, S. Tanaka, S. Nomura, P. Riblet, and Y. Aoyagi, Appl. Phys. Lett. 73, 1104 (1998).
[46] Y. P. Varshni, Physica (Amsterdam) 34, 149 (1967).
[47] Y. T. Dai, J. C. Fan, Y. F. Chen, R. M. Lin, S. C. Lee, and H. H. Lin, J. Appl. Phys.
82, 4489 (1997).
[48] M. Leroux, N. Grandjean, B. Beaumont, G. Nataf, F. Semond, J. Massies, and P.
Gibart, J. Appl. Phys. 86, 3721 (1999).
[49] C. S. Yang, Y. J. Lai, W. C. Chou, W. K. Chen, M. C. Lee, M. C. Kuo, J. Lee, J. L.
Shen, D. J. Jang, and Y. C. Cheng, J. Appl. Phys. 97, 033514 (2005).
[50] M. Funato, A. Balocchi, C. Bradford, K. A. Prior, and B. C. Cavenett, Appl. Phys.
Lett. 80, 443 (2002).
[51] Annamraju Kasi Viswanath, Joo In Lee, Sungkyu Yu, Dongho Kim, Yoonho Choi and Chang-hee Hong, Appl. Phys. Lett. 84, 3848 (1998).