The effect of different oriented sapphire substrates on the growth of polar and non-polar ZnMgO by MOCVD

Shi, Kai; Yang, Anli; Wang, J.; Song, Hang; Xu, Xiaoqing; Sang, Ling; Wei, Hongyuan; Yang, Shuangqiao; Liu, X.L.; Zhu, Qinsheng; Wang, Z.G.

doi:10.1016/j.jcrysgro.2010.11.095

Cited by 4 publications

(1 citation statement)

References 26 publications

(39 reference statements)

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“…The former is the near-band-edge (NBE) emission attributed to the recombination of excitons through an exciton-exciton collision process, and the latter is attributed to deep level defects, possibly be summed up to be zinc interstitials, oxygen vacancies, zinc vacancies, oxygen interstitials, or donor-acceptor transitions between defects complex. The intensity of NBE emission from the a-ZnO film is at least five times as that from the c-ZnO film, different from previous studies on in-plane polar ZnO films on sapphire; for instance, Shi et al [28] fabricated the cZnO, a-ZnO, and m-ZnO on c-Al 2 O 3 , r-Al 2 O 3 , and mAl 2 O 3 , respectively, and found weaker NBE emissions from the a-ZnO and m-ZnO than that from the c-ZnO. On the other hand, for well-prepared GaN, the nonpolar oriented films and quantum wells usually benefit to enhanced PL intensities [29].…”

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confidence: 97%

Enhanced near-band-edge emission from a-plane ZnO thin films on SrTiO3 substrates

Liu

et al. 2015

Appl. Phys. A

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Epitaxial ZnO with controlled orientations is highly concerned, and we report epitaxial growth of (0001)-and (11-20)-oriented ZnO films, respectively, on (111)-and (100)-SrTiO 3 (STO) substrates using pulsed laser deposition. The epitaxial growth of (11-20)-ZnO films on (100)-STO, with in-plane orientation relationship of ZnO [0001]//STO [110] and ZnO [10-10]//STO [1-10], is realized. It is revealed that the (11-20)-ZnO films have much stronger photo-luminescence (PL) intensity than those of the (0001)-oriented ones, while the electric conductance remains comparable with the latter. The electrical and PL properties of the (11-20)-ZnO films are correlated with the in-plane polarity.Zinc oxide (ZnO) is one of the most extensively investigated semiconductors [1][2][3]. In the ambient conditions, it crystallizes in wurtzite structure, which has a hexagonal unit cell with the P6 3 mc space group and lattice parameters a = 0.32475 nm and c = 0.52042 nm. Widespread interest in ZnO is fueled by its prospects in optoelectronics applications [4,5]. It is known that ZnO and GaN both have wide band-gap (E g ) of *3.3 eV at 300 K. However, ZnO shows some advantages over GaN, such as the availability of high-quality ZnO single crystals and thin films, resulting in a potentially low cost for processing relevant devices. The most attractive advantage of ZnO over GaN is the high exciton binding energy which is 25 meV for GaN but 60 meV for ZnO, while the roomtemperature (RT) thermal energy is *25 meV [6]. This allows the specific preference of ZnO for intense nearband-edge exciton emission at higher temperatures.Another well-recognized application associated with ZnO is transparent thin-film transistor [7], where the protective covering preventing light exposure is eliminated since ZnO-based transistors are insensitive to visible light. More importantly, a carrier density up to 2 9 10 21 cm -3 can be reached in ZnO by heavy substitution [8], allowing the electrical properties to be modulated in a broad regime, while its optical transparency remains robust, making it useful for transparent electrodes [9, 10]. These advantages even promise ZnO as a material for spintronics since good magnetic properties can be induced by magnetic substitutions [11].Along this line, high-quality ZnO epitaxial films with different orientations are highly appealed for developing ZnO-based devices. Successful preparations of (0001)-oriented ZnO (c-ZnO) films on various substrates including sapphire have been well reported [12,13]. However, defects are easily generated in epitaxial ZnO films on the sapphire due to the large lattice mismatch of 18 % [14], including misfit dislocations [15,16] and twin domains [14,17,18]. On the other hand, increasing attentions are paid to obtain in-plane polar epitaxial ZnO films, such as (10-10)-oriented (m-plane) and (11-20)-oriented (a-plane) ones [19]. It is known that ZnO has its intrinsic electrical polarity along the c-axis in the wurtzite structure, and thus, the c-ZnO thin films inevitably suffer the quantum-c...

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confidence: 97%