Phase Segregation of ZnO / ZnMgO Superlattice Affected by Ⅱ-Ⅵ Ratio

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1 CHINESE JOURNAL OF LUMINESCENCE Vol. 35 No. 5 May Ⅱ-Ⅵ ZnO /ZnMgO * 3615 Zn 1 - x Mg x O x =. 4 ~. 6 c ZnO /ZnMgO Ⅱ-Ⅵ X X MgZnO ZnO Ⅱ-Ⅵ O A DOI /fgxb Phase Segregation of ZnO / ZnMgO Superlattice Affected by Ⅱ-Ⅵ Ratio WANG Hao ZHAN Hua-han * CHEN Xiao-hang ZHOU Ying-hui WANG Hui-qiong KANG Jun-yong Department of Physics Xiamen University Xiamen 3615 China * Corresponding Author huahan@ xmu. edu. cn Abstract ZnMgO alloy allows for tunable optoelectronic devices. However the compositional range between ZnO and MgO is interrupted by a crystalline miscibility gap where the wurtzite crystal structure of ZnO is structurally incompatible with the rocksalt structure of MgO. In this article ten periods of ZnO / ZnMgO superlattice were produced by plasma-assistant molecular beam epitaxy on c- plane sapphire substrate with different oxygen condition. It is found that the sample grown at lower oxygen flow and radio-frenquency RF plasma power tends to form rocksalt phase. With the increase of oxygen flow and RF plasma power wurtzite phase tends to dominate and phase segregation is enhanced. The phase transform affected by the oxygen atoms density is reasoned by the formation enthalpies of ZnO and MgO. Key words MgZnO ZnO superlattice Ⅱ-Ⅵ ratio phase segregation 1 GaN ZnO ZnO MgO ZnO ev ZnO

2 5 Ⅱ-Ⅵ ZnO /ZnMgO 527 AFM MgO ZnO Varian Cary 3 - Mg. 4 ~. 6 2 ~ 8 nm ZnMgO PHI PHI 5C ESCA System MgO ZnO X XPS 45% 1 C 1s ev ZnMgO Fujita 2-3 c a MgO /ZnO ZnMgO Ⅱ-Ⅵ 1 AFM 1 a ZnMgO 1 1 b 4 2 ZnMgO 5 2 ZnO /ZnMgO 6 ZnO Ⅱ-Ⅵ Zn 1 O Omicron PA-MBE c 1 Mg ZnO /ZnMgO c 3 RMS:.34 nm MBE 1 h min 滋 m 4 Mg 45 1 nm ZnO /ZnMgO Mg 66% ZnO 3 nm ZnMgO 9 nm O Ⅱ-Ⅵ 1 O Pa O 2 W 2 O Pa O 25 W Philips Panalytical X'pert Pro X XRD X Cu Kα Fig. 1 4 kv 3 ma 3 2 XRD 2 1 (a) (b) RMS:1.89 nm 滋 m nm a 2 b AFM Morphology of sample 1 a and sample 2 b scanned by AFM

3 Wurzite phase ZnMgO(1) Rock salt phase Sample 1 ZnO(1) Sample 兹 / ( ) ZnMgO(111) MgO(111) Al 2O 3(11) 1 2 XRD θ-2θ Fig. 2 XRD θ-2θ spectra of sample 1 and sample 2 1 Al 2 O θ-2θ Al 2 O Sample MgO Sample ZnMgO ZnMgO MgO b 3 2 ZnMgO 姿 /nm ~ 8 nm Fig. 3 Transmission spectra of sample 1 and sample 2 from MgO RS-ZnMgO Zn Mg 1 Boutwell 4 ZnMgO 1 ZnMgO Mg Zn 1 Zn Mg 1 ZnMgO 2 ZnO ZnO 1% nm 174 nm nm ZnO 2 nm MgO 7. 8 ev MgO 2 nm XRD 1 2 Mg Transmission/% 2 to 8 nm X XPS ZnMgO ev Mg 5. 2 ev Mg I Mg2 p /F Mg2 p X Mg = 1 Zn I Mg2 p /F Mg2p + I Zn2 p 3 /F Zn2 p 3 ZnMgO I XPS F F Mg2p =. 7 F Zn2 p 3 = Auger Scan MgO Mg 56. 2% 2 Mg 64. 6% ZnO ZnMgO 1 27 nm O XRD

4 5 Ⅱ-Ⅵ ZnO /ZnMgO 529 O O Zn Mg ZnO ev ZnO MgO ev ZnO kj / 1 mol 4 MgO - 61 kj /mol 4 1 Mg 2p MgO ZnO O 1 Zn Mg O Mg Mg Zn O ZnO O O 1s Dutta 8 Zn ZnO Mg- XPS 4 Zn Zn i 1 Zn 2p 3 / ev ZnO ZnO n Zn 2p 3 / Mg Zn -Zn i Mg-s O-p Zns p O 1s Zn 2p 3 /2 Mg 2p ev 2 Zn 2p 3 / ev 1 4 Mg-s O-p Zn-s 4 1 p Zn 1 XPS Liu 9 ZnMgO Zn XPS cm - 3 Zn 2p 3 /2 Zn Zn i ZnO XRD 1 XPS (a) (b) 1-Zn 2p 3/2 1-Mg 2p (c) (d) 2-Zn 2p 3/2 2-Mg 2p Fig a b 2 c d Zn Mg XPS Zn 2p 3 /2 spectra of sample 1 a and sample 2 c Mg 2p spectra of sample 1 b and sample 2 d.

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