Controlled growth of O-polar ZnO epitaxial film by oxygen radical preconditioning of sapphire substrate

Mei, Z. X.; Wang, Yong; Du, Xiaolong; Ying, Minju; Zeng, Zhigang; Zheng, Hao; Jia, Jin‐Feng; Xue, Qi‐Kun; Zhang, Z.

doi:10.1063/1.1812362

Cited by 39 publications

(17 citation statements)

References 23 publications

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“…Oxygen atoms then bond to the Zn atoms while occupying the tetrahedral sites of ZnO, similar to AlN formation on the O-terminated (0001) Al 2 O 3 by nitridation. 23 Therefore, every oxygen atom has one dangling bond along the c-direction, which results in O-polarity. As a result, the ZnO films on Cr 2 O 3 had O-polarity.…”

Section: Evaluation Of Polaritymentioning

confidence: 99%

Growth of Polarity-Controlled ZnO Films on (0001) Al2O3

Park

Chang

Minegishi

et al. 2007

Journal of Elec Materi

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The polarity control of ZnO films grown on (0001) Al 2 O 3 substrates by plasmaassisted molecular-beam epitaxy (P-MBE) was achieved by using a novel CrN buffer layer. Zn-polar ZnO films were obtained by using a Zn-terminated CrN buffer layer, while O-polar ZnO films were achieved by using a Cr 2 O 3 layer formed by O-plasma exposure of a CrN layer. The mechanism of polarity control was proposed. Optical and structural quality of ZnO films was characterized by high-resolution X-ray diffraction and photoluminescence (PL) spectroscopy. Low-temperature PL spectra of Zn-polar and O-polar samples show dominant bound exciton (I 8 ) and strong free exciton emissions. Finally, one-dimensional periodic structures consisting of Zn-polar and O-polar ZnO films were simultaneously grown on the same substrate. The periodic inversion of polarity was confirmed in terms of growth rate, surface morphology, and piezo response microscopy (PRM) measurement.

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Section: Evaluation Of Polaritymentioning

confidence: 99%

Growth of Polarity-Controlled ZnO Films on (0001) Al2O3

Park

Chang

Minegishi

et al. 2007

Journal of Elec Materi

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“…An interface structure featured with misfit dislocations between AlN and ZnO was found, and more details are available in our work published elsewhere. 16 Figure 3b shows the clear interfaces of ZnO/MgO/ AlN/Al 2 O 3 . Above the unrelaxed zincblende AlN layer, displays a significant nonuniform MgO buffer with~3-nm thickness.…”

mentioning

confidence: 96%

“…On the other hand, 3-D growth predominates over 2-D growth in the case of the two-buffer process due to the large lattice mismatch between ZnO and unrelaxed AlN. The misfit dislocation was found at the interface between the ZnO and unrelaxed AlN layer, 16 and the existence of a higher defect density results in an inferior crystal quality and rough surface morphology.…”

mentioning

confidence: 97%

“…[13][14][15] Pregrowth nitridation was employed in our previous experiments to modify the sapphire surface. 16,17 This two-buffer method was found to be able to achieve the growth of unipolar and single-domained ZnO films. In those works, however, we found that the AlN layer formed by sapphire nitridation is not relaxed.…”

mentioning

confidence: 98%

“…Detailed information can be found in our previous paper. 16,17 On the nitrided sapphire substrate, MgO patterns overlap on AlN patterns (MgO½111//AlN½111, MgO½112//AlN½112). This follows a typical Stranski-Krastanov growth mode, that is, an initial twodimensional (2-D) wetting layer and a subsequent three-dimensional (3-D) island growth (not shown here).…”

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confidence: 99%

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Tri-Buffer Process: A New Approach to Obtain High-Quality ZnO Epitaxial Films on Sapphire Substrates

Wang

Ying

et al. 2007

Journal of Elec Materi

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A tri-buffer method was applied to achieve layer-by-layer growth of highquality ZnO films on sapphire (0001) substrates by rf plasma-assisted molecular beam epitaxy (MBE). After sufficient nitridation of the substrate, MgO and ZnO buffer layers were subsequently deposited on the resulting AlN layer. An atomically smooth ZnO surface with a roughness less than 1 nm in a 10 lm · 10 lm scanned area was obtained with this method. The crystal quality was also improved, as characterized by reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The results indicate that the tri-buffer process could reduce the large lattice mismatch between ZnO and nitrided sapphire and facilitate the two-dimensional (2-D) growth of the ZnO epilayer. A model is proposed to understand the observations. During the last decade, developments in the field of ZnO-based wide band gap materials have been striking. Currently, high-quality epitaxial layers can be grown by various methods, and efforts can be made on the fabrication of related optoelectronic devices. 1-11 By far, most studies have been focused on ZnO-on-sapphire heteroepitaxy 6,7 due to the high crystal quality, low cost, and hexagonal surface structure of sapphire substrates. However, the large lattice mismatch (18.3%) and thermal expansion mismatch (-13.2 and -64.5% perpendicular and parallel to the c direction, respectively) between ZnO and c-plane sapphire make the high-quality film growth difficult and complex. Some buffer techniques have been developed to solve this problem. Deposition of a low-temperature (LT) ZnO nucleation layer has been widely used prior to hightemperature (HT) epilayer, 12 and high-quality ZnO growth on MgO-buffered sapphire substrate has been thoroughly studied and optimized. 13-15 Pregrowth nitridation was employed in our previous experiments to modify the sapphire surface. 16,17 This two-buffer method was found to be able to achieve the growth of unipolar and single-domained ZnO films. In those works, however, we found that the AlN layer formed by sapphire nitridation is not relaxed. Hence, the mismatch between ZnO and AlN is still as large as 18.3%, which makes further improvements in crystal quality impossible. In this paper, we report our approach to this issue by applying a tri-buffer process, that is, inserting a thin MgO layer between the ZnO and AlN layers. It was found that MgO can reduce the large lattice mismatch and facilitate the nucleation. An atomically smooth ZnO epilayer with improved quality was obtained, as confirmed by reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM).The ZnO samples were prepared on sapphire (0001) substrates using an rf plasma-assisted molecular beam epitaxy (MBE) system. The base pressure in the growth chamber was~1 · 10 )10 Torr. The substrates were preconditioned by oxygen plasma at 180°C and then exposed to...

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Controlled Growth of High‐Quality ZnO‐Based Films and Fabrication of Visible‐Blind and Solar‐Blind Ultra‐Violet Detectors

et al. 2009

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ZnO is a wide‐bandgap (3.37 eV at room temperature) oxide semiconductor that is attractive for its great potential in short‐wavelength optoelectronic devices, in which high quality films and heterostructures are essential for high performance. In this study, controlled growth of ZnO‐based thin films and heterostructures by molecular beam epitaxy (MBE) is demonstrated on different substrates with emphasis on interface engineering. It is revealed that ultrathin AlN or MgO interfacial layers play a key role in establishing structural and chemical compatibility between ZnO and substrates. Furthermore, a quasi‐homo buffer is introduced prior to growth of a wurtzite MgZnO epilayer to suppress the phase segregation of rock‐salt MgO, achieving wide‐range bandgap tuning from 3.3 to 4.55 eV. Finally, a visible‐blind UV detector exploiting a double heterojunction of n‐ZnO/insulator‐MgO/p‐Si and a solar‐blind UV detector using MgZnO as an active layer are fabricated by using the growth techniques discussed here.

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Controlled growth of O-polar ZnO epitaxial film by oxygen radical preconditioning of sapphire substrate

Abstract: Articles you may be interested inDirect correlation between the internal quantum efficiency and photoluminescence lifetime in undoped ZnO epilayers grown on Zn-polar ZnO substrates by plasma-assisted molecular beam epitaxy

Cited by 39 publications

References 23 publications

Growth of Polarity-Controlled ZnO Films on (0001) Al2O3

Growth of Polarity-Controlled ZnO Films on (0001) Al2O3

Tri-Buffer Process: A New Approach to Obtain High-Quality ZnO Epitaxial Films on Sapphire Substrates

Controlled Growth of High‐Quality ZnO‐Based Films and Fabrication of Visible‐Blind and Solar‐Blind Ultra‐Violet Detectors

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