Lattice Dynamics and Crystalline Properties of Wurtzite Zn1–xMgxO Powders under High Pressure

Lin, Yan; Tseng, Cheng-Lung; Chou, Wu–Ching; Chia, C. H.; Han, T. C.; Shen, Ji‐Lin

doi:10.1021/jp207691c

Cited by 12 publications

(4 citation statements)

References 43 publications

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“…The shift towards the lower frequency may be suggestive of a relaxation of intrinsic compressive stress. The pressure coefficient ðvu=vPÞ for the LO-mode in ZnO (where u is the phonon frequency) was found previously to be in the range of 4.14e4.56 cm À1 /GPa [49,50]; a similar pressure coefficient, 4.9 cm À1 /GPa, was obtained by our group for the case of ZnO doped with a small percentage of Mg [51]. Since the observed Raman shift is~5 cm À1 , a relaxation of~1 GPa took place upon annealing.…”

Section: Raman Studysupporting

confidence: 80%

Achieving highly-enhanced UV photoluminescence and its origin in ZnO nanocrystalline films

et al. 2016

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a b s t r a c tZnO is an efficient luminescent material in the UV-range~3.4 eV with a wide range of applications in optical technologies. Sputtering is a cost-effective and relatively straightforward growth technique for ZnO films; however, most as-grown films are observed to contain intrinsic defects which can significantly diminish the desirable UV-emission. In this research the defect dynamics and optical properties of ZnO sputtered films were studied via post-growth annealing in Ar or O 2 ambient, with X-ray diffraction (XRD), imaging, transmission and Urbach analysis, Raman scattering, and photoluminescence (PL). The imaging, XRD, Raman and Urbach analyses indicate significant improvement in crystal morphology and band-edge characteristics upon annealing, which is nearly independent of the annealing environment. The native defects specific to the as-grown films, which were analyzed via PL, are assigned to Zn i related centers that luminesce at 2.8 eV. Their presence is attributed to the nature of the sputtering growth technique, which supports Zn-rich growth conditions. After annealing, in either environment the 2.8 eV center diminished accompanied by morphology improvement, and the desirable UV-PL significantly increased. The O 2 ambient was found to introduce nominal O i centers while the Ar ambient was found to be the ideal environment for the enhancement of the UV-light emission: an enhancement of~40 times was achieved. The increase in the UV-PL is attributed to the reduction of Zn i -related defects, the presence of which in ZnO provides a competing route to the UV emission. Also, the effect of the annealing was to decrease the compressive stress in the films. Finally, the dominant UV-PL at the cold temperature regime is attributed to luminescent centers not associated with the usual excitons of ZnO, but rather to structural defects.

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Section: Raman Studysupporting

confidence: 80%

Achieving highly-enhanced UV photoluminescence and its origin in ZnO nanocrystalline films

et al. 2016

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“…It has been reported experimentally that the ZnO B1 phase reconverts to the B4 phase when the high pressure decompresses to ambient pressure. Therefore, it might be a smart strategy to enhance p‐type doping, that is, the concentration of V Zn defects and the P Zn –2V Zn complex, by performing impurity doping under high compression and then release the strain completely, or to follow the method proposed by Lin et al and to prepare a ZnO B1 phase with a high concentration of p‐type defects under ambient pressure 66. This would broaden the application span of photodetection and photovoltaic devices.…”

Section: Resultsmentioning

confidence: 99%

Strain‐Engineered Modulation on the Electronic Properties of Phosphorous‐Doped ZnO

Dai

Wei

et al. 2013

ChemPhysChem

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The modulation of strain on the electronic properties of ZnO:P is investigated by density functional theory calculations. The variation of formation energy (E(f)) and band structure with strains ranging from -0.1 to 0.1 are considered. Although both the conduction band minimum (CBM) and the valence band maximum of ZnO are antibonding states, the CBM is more sensitive to strain, reducing the band gap with an increase in strain. P-substituted O (PO) defects show poor p-type conductivity due to a smaller E(f) and lower lying acceptor levels as a consequence of lattice expansion. The E(f) of P-substituted Zn (PZn) defects decreases under tension, owing to the release of strong repulsive stress induced by excess electrons from PZn. The donor energy band of PZn broadens under tensile strain, which benefits n-type conductivity. For Zn vacancies (VZn) and PZn-2VZn complexes, the distances between the O atoms around VZn are so large that repulsive and attractive interactions become weak, which results in an easy release of the strain. We herein present for the first time that the E(f) values of VZn and PZn-2VZn complexes decrease under both tension and compression, or in the high-pressure rock-salt phase. Under a strain of 0.1 the PZn-2VZn complex shows the smallest E(f). Under -0.07 strain the wurtzite/rock-salt phase transition occurs and the direct band gap becomes an indirect one. The variation of band structures in the rock-salt phase is similar to that in the wurtzite phase. Consequently, the p-type conductivity of ZnO:P can be improved with an increase in solubility of PZn-2VZn or VZn defects.

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“…High-pressure PL and TRPL measurements were all made at room temperature using a ruby-calibrated diamond anvil cell (DAC). 15 The pressure-transmitting medium was Milli-Q water (Millipore), and the pressure gradient was less than 0.2 GPa throughout the sample chamber. The PL and TRPL of the CdTe NCs and the ruby fluorescence were excited using a 200 ps pulsed laser diode (405 nm/2.5 MHz/1 mW), which was focused onto the sample using a 20× Olympus objective with a long working distance.…”

Section: Methodsmentioning

confidence: 99%

Water-soluble CdTe nanocrystals under high pressure

Lin

2015

SPIE Proceedings

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The application of static high pressure provides a method for precisely controlling and investigating many fundamental and unique properties of semiconductor nanocrystals (NCs). This study systematically investigates the high-pressure photoluminescence (PL) and time-resolved carrier dynamics of thiol-capped CdTe NCs of different sizes, at different concentrations, and in various stress environments. The zincblende-to-rocksalt phase transition in thiol-capped CdTe NCs is observed at a pressure far in excess of the bulk phase transition pressure. Additionally, the process of transformation depends strongly on NC size, and the phase transition pressure increases with NC size. These peculiar phenomena are attributed to the distinctive bonding of thiols to the NC surface. In a nonhydrostatic environment, considerable flattening of the PL energy of CdTe NCs powder is observed above 3.0 GPa. Furthermore, asymmetric and double-peak PL emissions are obtained from a concentrated solution of CdTe NCs under hydrostatic pressure, implying the feasibility of pressure-induced interparticle coupling.

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Lattice Dynamics and Crystalline Properties of Wurtzite Zn_1–xMg_xO Powders under High Pressure

Cited by 12 publications

References 43 publications

Achieving highly-enhanced UV photoluminescence and its origin in ZnO nanocrystalline films

Achieving highly-enhanced UV photoluminescence and its origin in ZnO nanocrystalline films

Strain‐Engineered Modulation on the Electronic Properties of Phosphorous‐Doped ZnO

Water-soluble CdTe nanocrystals under high pressure

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