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1 Vol. 27, No. 12, pp , 2006 ZnO Growth Morphologies and Lattice Defects in Wide-gap Semiconductor ZnO Films Hiroaki MATSUI and Hitoshi TABATA Center for the Promotion of Research on Nanoscience and Nanotechnology, Osaka University, 13 Machikaneyamacho, Toyonaka, Osaka Institute of Scientific and Industrial Research Sanken, Osaka University, 81 Mihogaoka, Ibaraki, Osaka (Received September 12, 2006) Oxide materials with strong ionicity are associated with a large number of lattice defects because the defect formation enthalpy is very low. The control of growth mode and lattice defects in film growth of hexagonal ZnO plays an important role in producing new functional applications utilizing optical, magnetic and electrical properties. Thus far, we have investigated growth mode, optical and electrical characterizations in ZnO films in relation to polarity and non-polarity. In this report, we present a correlation between surface morphology and growth direction, and then show that optical and electrical properties were closely related to lattice defects generated in the host. Furthermore, we introduce self-organization of surface nanostructures and a local phase separation induced by interface defects in heteroepitaxial growth with lattice mismatch. 1 ZnOTiO2SrTiO3 12 PLD 3 ZnO Zn n tabata@sanken.osaka-u.ac.jp ZnO Ga Zn 4 ZnO n p 5 Stranski- KrastanovS-K 6 ZnO 22

ZnO Eagle-Picher Co., 6 N Fig. 1 AFM 1.4 10 4 mbar 6 N ZnO Fig. 1a1.

010 4 mbar Fig. 1dGaN 8 000211-24 X FWHM4090 10 8 10 9 cm 2 Fig.

2 709 AFM X 2Zn Zn ZnO Zn Zn Zn ZnO ZnO0001Crystal GmbH, 4NTg420 7 ZnO Eagle-Picher Co., 6 N Fig. 1 AFM mbar 6 N ZnO Fig. 1a mbar Fig. 1b mbar 0.4 nm ZnO c nm c Fig. 1c mbar Fig. 1dGaN X FWHM cm 2 Fig. 1ec Zn Zn Zn 1 Zn Zn O-rich N N2 ZnO 9 Eb9.76 ev Eb5.12 ev Zn O Zn Fig.1 GaN Ga Fig. 1. (a)-(d) AFM top images and cross-sectional line profiles of ZnO films fabricated at Tg420 under the different growth conditions;( e) Schematic images of O- and Zn-terminated surfaces along the Zn-polar direction in ZnO lattice. 23

3 Fig. 2. (a)-(d) Low-temperature PL spectra at 10 K and electrical properties for ZnO films grown at Tg420 under ap(o2)of(a) , (b) , (c) and (d) mbar. Oxygen flux was supplied by O2 plasma exposure (a) or O2 gas flow (b-d). (e) Electron concentration (ne) as a function of reciprocal temperature for ZnO films at Tg550 and ZnO (E.P.) single crystal. The solid line represents theoretical fits according to Eq. ( 1 ). Inset figure shows dependence of Hall mobility for ZnO films and ZnO (E.P.) single crystal on measurement temperature. Ga Ga Ga-rich Fig K1.6 mw PL ev D X 3.15 ev Fig. 2 a ZnZniVO cm cm 2 V.s 3.15 ev Fig. 2b mbar Fig. 2c 3.3 mev MBE 11 ZnO MBE Zn 12 Zn ZnO mbar ZnO cm 3 84 cm 2 V.s mbar Fig. 2d Zn VZn Fig. 2eTg550 ZnO ZnO 6 N Ed 13 ND nena 1gd ne Ed exp NC kbt gd g1 2, degeneracy factor g0 1 Nc kb ND NA ZnO 35 mev 75 mev Zni AlZnGaZn 14 ZnO Ed 39 mev 45 mev Zni ZnO ND-NA ZnO Zni 300 K 100 K ZnO cm 2 V.s ZnO 105 cm 2 V.s300 K 280 cm 2 V.s100 K300 K 430 cm 2 V.s cm 3 Zni 24

711 ZnO 16 ZnO000-110 16 cm 3 3 Mg Mg0.37Zn0.63OZnO 3. 1 S-K S-K Fig. 3atMg x MgxZn1xO MgxZn1xOx 0.27ZnO Mg 37 MgO ZnO Mg0.37 Zn0.63O t38 nm t65 nm Fig. 3b Mg0.37Zn0.63O t100 nm AFM 17 ZnO 0.

3 ev 4.0 ev Mg Fig. 3. (a) Dependence of film thickness on Mg content (x) for MgxZn1xO films from a viewpoint of growth mode. (b) AFM top image of the Mg0.37Zn0.63O layers with thickness of 100 nm.

4 711 ZnO 16 ZnO cm 3 3 Mg Mg0.37Zn0.63OZnO 3. 1 S-K S-K Fig. 3atMg x MgxZn1xO MgxZn1xOx 0.27ZnO Mg 37 MgO ZnO Mg0.37 Zn0.63O t38 nm t65 nm Fig. 3b Mg0.37Zn0.63O t100 nm AFM 17 ZnO nm Mg0.37Zn0.63O nm 0.52 S-K Mg0.37Zn0.63O X RSM 17 Fig. 3c d38 nm 100 nm Mg0.37Zn0.63O RSM t38 nm Qx t100 nm hcfig. 3a 38 nm 65 nm Matthews 18 hc38 nm 3. 2 MgZnO Mg Zn MgxZn1xO Mg 3.3 ev 4.0 ev Mg Fig. 3. (a) Dependence of film thickness on Mg content (x) for MgxZn1xO films from a viewpoint of growth mode. (b) AFM top image of the Mg0.37Zn0.63O layers with thickness of 100 nm. Reciprocal space mapping of the (11-24) reflection for Mg0.37Zn0.63O films with thickness of (c) 38 nm and (d) 100 nm. 17 Fig. 4a Mg0.37Zn0.63 O t38 nm 4.0 ev t100 nm 280 nm hυ 3.7 ev SEM CL hυ3.96 evmg SEM CL Fig. 4be 19 S-K In0.19Ga0.81N In

712 27 12 2006 Fig. 4. ( a) Dependence of μ -PL spectra on Mg0.37Zn0.63O layers thickness.

Note that the two bright spots do not indicate surface morphology but dust used for a correction of focusing of the electron beam; (c) Monochromatic

1 ZnO10-1011-20M A M A ZnO Fig. 5 a 5 b M A AFM 22 M 10 5 cm 1 0001 5 μm M Zn-O 00012 1-210Fig. 5c 23 A Zn-O 0001 8 Fig. 5dA 1-100 00010001 8 2 M Fig. 5. AFM top images of the ZnO films with growth direction of (10-10) (a) and (11-20) (b).

5 Fig. 4. ( a) Dependence of μ -PL spectra on Mg0.37Zn0.63O layers thickness. A forth harmonic generation of Nd: YAG laser (λ 266 nm) was used as an excitation source: (b) Topological surface image. Note that the two bright spots do not indicate surface morphology but dust used for a correction of focusing of the electron beam; (c) Monochromatic cathodoluminescence image taken at 3.90 ev; (d) and (e) show the crosssection profiles of X- and Y-lines indicated by the white dot lines. Mg0.37Zn0.63O ZnO M A M A ZnO Fig. 5 a 5 b M A AFM 22 M 10 5 cm μm M Zn-O Fig. 5c 23 A Zn-O Fig. 5dA M Fig. 5. AFM top images of the ZnO films with growth direction of (10-10) (a) and (11-20) (b). (c) and (d) show schematic top views of the ZnO (10-10) and (11-20) lattices Fig. 6 Tg420 Zn σ Fig. 6a 150 K 400 σ K σ EdkBT Kσ T 1 σ1-210 Mott σ T 14 VRH 25 Fig. 6c K μ μ0001μ Tx1.5 x x μ11-20 x x3.62 x1.5 26

6 ZnO TiO2 SrTiO Fig. 6. (a) Dependence of conductivity parallel (σ.0001) and perpendicular (σ.11-20) to the nanostripe arrays on reciprocal temperature. Inset figure shows conductivity versus T 14 dependence in the11-20direction. (b) Electron concentration (ne) as a function of reciprocal temperature. The solid line represents theoretical fits according to Eq. (1); Dependence of Hall mobility parallel (μ H0001) and perpendicular (μ H11-20) to the nanostripe arrays on reciprocal temperature. The aforementioned data were obtained for the ZnO film at Tg420. x1 GaN 300 K σ T 14 VRH 26 μ11-20expφ bkbt Φ b68.3 mev GaN Φ b 69 mevfig. 6b ne1 Ed37 mevnd NA cm cm 3 NAND0.42 VZn 1) Y.F. Chen, D.M. Bagnall, Z. Zhu, T. Sekiuchi, K.T. Park, K.Hiraga,T.Yao,S.Koyama,M.Y.ShenandT.Goto: J. Cryst. Grwoth 181, 165 (1997). 2) Y.F. Chen, D.M. Bagnall, H.J. Ko, K.T. Park, Z. Zhu and T. Yao: J. Appl Phys. 84, 3912 (1998). 3) R.D. Vispute, V. Talyansky, Z. Trajanovic, S. Choopun, M. Downes, P.P. Shrma and T. Venkatesan: Appl. Phys. Lett. 70, 2735 (1997). 4) H. Kato, M. Sano, K. Miyamoto and T. Yao: J. Cryst. Growth , 538 (2002). 5) A. Tsukazaki, A. Ohtomo, T. Onuma, M. Ohtani, T. Makino, M. Sumiya, K. Ohtani, S.F. Chichibu, S. Fuke, Y. Segawa, H. Koinuma and M. Kawasaki: Nat. Mater. 4, 42 (2005). 6) M. Sumiya, K. Yoshimura, K. Ohtsuka and S. Fuke: Appl. Phys. Lett. 76, 2098 (2000). 7) H. Matsui, H. Saeki, T. Kawai, A. Sasaki, M. Yoshimoto, M. Tsubaki and H. Tabata: J. Vac. Sci. Technol. B 22, 2452 (2004). 8) B. Heying, R. Averbeck, L.F. Chen, E. Haus, H. Riechert and J.S. Speck: J. Appl. Phys. 88, 1855 (2000). 9) H. Matsui, H. Saeki, T. Kawai, B. Mizobuchi and H. Tabata: J. Appl. Phys. 95, 5882 (2004). 10) E.J. Tarsa, B. Heying, X.H. Wu, P. Fini, S.P. DenBaars and J.S. Speck: J. Appl. Phys. 82, 5472 (1997). 11) M.A. Herman and H. Sitter: Molecular Beam Epitaxy (Springer, Berlin, 1996). 12) H. Kato, M. Sano, K. Miyamoto and T. Yao: Jpn. J. Appl. Phys., Part 1 42, 2241 (2003). 13) R. Schaub, G. Pensl, M. Schulz and C. Holm: Appl. Phys. A 34, 215 (1984). 14) D.C. Look, G.C. Farrow, P. Reunchan, S. Limpijumnong, S.B. Zhang and K. Nordlund : Phys. Rev. Lett. 95, 27

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42 1 Fig. 2. Li 2 B 4 O 7 crystals with 3inches and 4inches in diameter. Fig. 4. Transmission curve of Li 2 B 4 O 7 crystal. Fig. 5. Refractive index

$42 1 Fig. 2. Li 2 B 4 O 7 crystals with 3inches and 4inches in diameter. Fig. 4. Transmission curve of Li 2 B 4 O 7 crystal. Fig. 5. Refractive index$ MEMOIRS OF SHONAN INSTITUTE OF TECHNOLOGY Vol. 42, No. 1, 2008 Li 2 B 4 O 7 (LBO) *, ** * ** ** Optical Scatterer and Crystal Growth Technology of LBO Single Crystal For Development with Optical Application