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Zhao, Qingxiang
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Publications (10 of 51) Show all publications
Zhao, Q., Liu, X. & Holtz, P.-O. (2014). Properties of shallow donors in ZnMgO epilayers grown by metal organic chemical vapor deposition. Journal of Applied Physics, 116(18), 183508
Open this publication in new window or tab >>Properties of shallow donors in ZnMgO epilayers grown by metal organic chemical vapor deposition
2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 18, p. 183508-Article in journal (Refereed) Published
Abstract [en]

High quality Zn1-xMgxO epilayers have been grown by means of metal organic chemical vapor deposition technique on top of ZnO templates. The grown samples were investigated by x-ray photoelectron spectroscopy and photoluminescence. The magnesium (Mg) concentration was varied between 0% and 3% in order to study the properties of shallow donors. The free and donor bound excitons could be observed simultaneously in our high quality Zn1-xMgxO epilayers in the photoluminescence spectra. The results indicate that both built-in strain and Mg-concentration influence the donor exciton binding energy. It clearly shows that the donor exciton binding energy decreases with increasing Mg-concentration and with increasing built-in strain. Furthermore, the results indicate that the donor bound exciton transition energy increases with decreasing strength of the built-in strain if the Mg-concentration is kept the same in the Zn1-xMgxO epilayers.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-113011 (URN)10.1063/1.4902007 (DOI)000345216300017 ()
Available from: 2015-01-12 Created: 2015-01-08 Last updated: 2017-12-05
Hsiao, C.-L., Palisaitis, J., Junaid, M., Persson, P. O., Jensen, J., Zhao, Q., . . . Birch, J. (2012). Room-temperature heteroepitaxy of single-phase Al1-xInxN films with full composition range on isostructural wurtzite templates. Thin Solid Films, 524, 113-120
Open this publication in new window or tab >>Room-temperature heteroepitaxy of single-phase Al1-xInxN films with full composition range on isostructural wurtzite templates
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2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 524, p. 113-120Article in journal (Refereed) Published
Abstract [en]

Al1-xInxN heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane AlN, GaN, and ZnO templates at room temperature (RT). Both Al1-xInxN single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AlN (similar to 13% mismatch), heteroepitaxy is achieved. However, RT-grown Al1-xInxN films directly deposited on non-isostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al1-xInxN structural quality with increasing indium content is attributed to the formation of more point-and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al1-xInxN films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown AlN layers thanks to their low amount of defects. We found that Vegards rule is applicable to determine x in the RT-grown Al1-xInxN epilayers if the lattice constants of RT-sputtered AlN and InN films are used instead of those of the strain-free bulk materials.

Place, publisher, year, edition, pages
Elsevier, 2012
Keywords
Magnetron sputter epitaxy, Aluminum indium nitride, Transmission electron microscopy, Sputtering, Vegards rule, Strain
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-86626 (URN)10.1016/j.tsf.2012.09.072 (DOI)000311410300018 ()
Note

Funding Agencies|Swedish Strategic Foundation||

Available from: 2012-12-20 Created: 2012-12-20 Last updated: 2018-03-08
Yang, L., Zhao, Q., Xing, G., Wang, D., Wu, T., Willander, M., . . . Yang, J. (2011). A SIMS study on Mg diffusion in Zn(0.94)Mg(0.06)O/ZnO heterostructures grown by metal organic chemical vapor deposition. Applied Surface Science, 257(20), 8629-8633
Open this publication in new window or tab >>A SIMS study on Mg diffusion in Zn(0.94)Mg(0.06)O/ZnO heterostructures grown by metal organic chemical vapor deposition
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2011 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 257, no 20, p. 8629-8633Article in journal (Refereed) Published
Abstract [en]

Zn(0.94)Mg(0.06)O/ZnO heterostructures have been grown on 2 in. sapphire wafer using metal organic chemical vapor deposition (MOCVD). Photoluminescence (PL) mapping demonstrates that Mg distribution on the entire wafer is very uniform (standard deviation of Mg concentration/mean Mg concentration = 1.38%) with average concentration of similar to 6%. The effect of annealing on the Mg diffusion in Zn(0.94)Mg(0.06)O/ZnO heterostructures has been investigated in detail by using secondary ion mass spectrometry (SIMS). All the Mg SIMS depth profiles have been fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn(0.94)Mg(0.06)O layer deposited at 700 degrees C is two orders of magnitude lower than that of annealed samples, which clearly indicates that the deposition temperature of 700 degrees C is much more beneficial to grow ZnMgO/ZnO heterostructures and quantum wells.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
Keywords
Heterostructures; Diffusion coefficient; Secondary ion mass spectrometry
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-69789 (URN)10.1016/j.apsusc.2011.05.038 (DOI)000291725100056 ()
Available from: 2011-08-10 Created: 2011-08-08 Last updated: 2017-12-08
Yang, L.-L., Zhao, Q., Willander, M., Liu, X., Fahlman, M. & Yang, J. H. (2010). Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process. Crystal Growth & Design, 10(4), 1904-1910
Open this publication in new window or tab >>Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process
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2010 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 10, no 4, p. 1904-1910Article in journal (Refereed) Published
Abstract [en]

ZnO nanorods arrays are respectively prepared under different vapor pressures with opening (OZN) or sealing (SZN) of the beaker. The results from time-resolved photoluminescence measurements indicate that sealing the beaker during the growth process can effectively suppress the surface recombination of ZnO nanorods, and the suppression effect is even better than a 500 degrees C post-thermal treatment or OZN samples. The results from X-ray photoelectron spectroscopy measurements reveal that the main reason for this phenomenon is that the surfaces of the SZN samples are attached by groups related to NH3 instead of the main surface recombination centers such as OH and groups in the OZN samples. The ammonia surface treatment on both OZN and SZN samples further testifies that the absorption of the groups related to NH3 does not contribute to the surface recombination on the ZnO nanorods.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54866 (URN)10.1021/cg100017b (DOI)000276234500068 ()
Note

This document is the Accepted Manuscript version of a Published Work that appeared in final form in CRYSTAL GROWTH and DESIGN, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see: Li-Li Yang, Qingxiang Zhao, Magnus Willander, Xianjie Liu, Mats Fahlman and J H Yang, Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process, 2010, CRYSTAL GROWTH and DESIGN, (10), 4, 1904-1910. http://dx.doi.org/10.1021/cg100017b Copyright: The American Chemical Society http://pubs.acs.org/

Available from: 2010-04-16 Created: 2010-04-16 Last updated: 2017-12-12Bibliographically approved
Yang, L. L., Zhao, Q., Israr, M. Q., Sadaf, J. R., Willander, M., Pozina, G. & Yang, J. H. (2010). Indirect optical transition due to surface band bending in ZnO nanotubes. Journal of Applied Physics, 108(10)
Open this publication in new window or tab >>Indirect optical transition due to surface band bending in ZnO nanotubes
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2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10Article in journal (Refereed) Published
Abstract [en]

ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 nm and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity.

Place, publisher, year, edition, pages
American Institute, 2010
Keywords
Zinc Oxide, Nanotube, Surface band bending, Indirect transition, Temperature-dependent photoluminescence
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-60853 (URN)10.1063/1.3511345 (DOI)000285005000053 ()
Note
Original Publication: Li Li Yang, Qingxiang Zhao, Muhammad Qadir Israr, Jamil Rana Sadaf, Magnus Willander, Galia Pozina and J. H. Yang, Indirect optical transition due to surface band bending in ZnO nanotubes, 2010, Journal of Applied Physics, (108), 10, 103513. http://dx.doi.org/10.1063/1.3511345 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12
Yang, L.-L., Zhao, Q., Willander, M., Liu, X., Fahlman, M. & Yang, J. H. (2010). Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy. Applied Surface Science, 256(11), 3592-3597
Open this publication in new window or tab >>Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy
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2010 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 11, p. 3592-3597Article in journal (Refereed) Published
Abstract [en]

The surface composition of as-grown and annealed ZnO nanorods arrays (ZNAs) grown by a two-step chemical bath deposition method has been investigated by X-ray photoelectron spectroscopy (XPS). XPS confirms the presence of OH bonds and specific chemisorbed oxygen on the surface of ZNAs, as well as H bonds on (1 0 (1) over bar 0) surfaces which has been first time observed in the XPS spectra. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Annealing can largely remove the OH and H bonds and transform the composition of the other chemisorbed oxygen at the surface to more closely resemble that of high temperature grown ZNAs, all of which suppresses surface recombination according to time-resolved photoluminescence measurements.

Place, publisher, year, edition, pages
Amsterdam, Netherlands: Elsevier, 2010
Keywords
ZnO nanorods, Optical properties, Surface recombination, X-ray photoelectron spectroscopy
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54620 (URN)10.1016/j.apsusc.2009.12.160 (DOI)000275515100042 ()
Note

Original Publication: Li-Li Yang, Qingxiang Zhao, Magnus Willander, Xianjie Liu, Mats Fahlman and J H Yang, Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy, 2010, APPLIED SURFACE SCIENCE, (256), 11, 3592-3597. http://dx.doi.org/10.1016/j.apsusc.2009.12.160 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2017-12-12
Pozina, G., Yang, L.-L., Zhao, Q., Hultman, L. & Lagoudakis, P. G. (2010). Size dependent carrier recombination in ZnO nanocrystals. APPLIED PHYSICS LETTERS, 97(13), 131909
Open this publication in new window or tab >>Size dependent carrier recombination in ZnO nanocrystals
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2010 (English)In: APPLIED PHYSICS LETTERS, ISSN 0003-6951, Vol. 97, no 13, p. 131909-Article in journal (Refereed) Published
Abstract [en]

Experimental and theoretical studies of fluorescence decay were performed for colloidal ZnO nanocrystals. The fluorescence lifetime reduces from 22 ps to similar to 6 ps with decreasing nanocrystal radius. We postulate that non-radiative surface states dominate the carrier dynamics in small ZnO nanocrystals and perform Monte Carlo simulations incorporating carrier diffusion and carrier recombination to model the experimental fluorescence decay dynamics. The percentage of excitons undergoing nonradiative decay due to surface trapping is as high as 84% for nanocrystals with 8 nm radius, which explains the ultrafast decay dynamics observed in small ZnO nanostructures even at low temperatures.

Place, publisher, year, edition, pages
American Institute of Physics, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-61208 (URN)10.1063/1.3494535 (DOI)000282443800028 ()
Note
Original Publication: Galia Pozina, Li-Li Yang, Qingxiang Zhao, Lars Hultman and P G Lagoudakis, Size dependent carrier recombination in ZnO nanocrystals, 2010, APPLIED PHYSICS LETTERS, (97), 13, 131909. http://dx.doi.org/10.1063/1.3494535 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2010-11-05 Created: 2010-11-05 Last updated: 2016-08-31
Yang, L.-L., Zhao, Q., Willander, M., Yang, J. H. & Ivanov , I. G. (2009). Annealing effects on optical properties of low temperature grown ZnO nanorod arrays. Journal of Applied Physics, 105(5), 053503-
Open this publication in new window or tab >>Annealing effects on optical properties of low temperature grown ZnO nanorod arrays
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2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 5, p. 053503-Article in journal (Refereed) Published
Abstract [en]

Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition method. The structure and optical properties of the grown ZnO nanorods were investigated by Raman and photoluminescence spectroscopy. The results showed that after an annealing treatment at around 500 degrees C in air atmosphere, the crystal structure and optical properties became much better due to the decrease in surface defects. The resonant Raman measurements excited by 351.1 nm not only revealed that the surface defects play a significant role in the as-grown sample, which was supported by low temperature time-resolved photoluminescence measurements, but also suggested that the strong intensity increase in some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defect scattering contribution for ZnO nanorods annealed from 500 to 700 degrees C.

Keywords
annealing, crystal structure, deep levels, II-VI semiconductors, liquid phase deposition, nanostructured materials, nanotechnology, photoluminescence, Raman spectra, time resolved spectra, wide band gap semiconductors, zinc compounds
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17508 (URN)10.1063/1.3073993 (DOI)
Note
Original Publication:Lili Yang, Qingxiang Zhao, Magnus Willander and Ivan Gueorguiev Ivanov , Annealing effects on optical properties of low temperature grown ZnO nanorod arrays, 2009, JOURNAL OF APPLIED PHYSICS, (105), 5, 053503.http://dx.doi.org/10.1063/1.3073993Copyright: American Institute of Physicshttp://www.aip.org/Available from: 2009-04-07 Created: 2009-03-27 Last updated: 2017-12-13Bibliographically approved
Wang, S. M., Zhao, H., Adolfsson, G., Wei, Y. Q., Zhao, Q., Gustavsson, J. S., . . . Larsson , A. (2009). Dilute nitrides and 1.3 mu m GaInNAs quantum well lasers on GaAs. MICROELECTRONICS JOURNAL, 40(3), 386-391
Open this publication in new window or tab >>Dilute nitrides and 1.3 mu m GaInNAs quantum well lasers on GaAs
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2009 (English)In: MICROELECTRONICS JOURNAL, ISSN 0026-2692 , Vol. 40, no 3, p. 386-391Article in journal (Refereed) Published
Abstract [en]

We present epitaxial growth of GaInNAs on GaAs by molecular beam epitaxy (MBE) using analog, digital and N irradiation methods. It is possible to realize GaInNAs quantum wells (QWs) with a maximum substitutional N concentration up to 6% and a strong light emission up to 1.71 mu m at 300 K. High quality 1.3 mu m GaInNAs multiple QW edge emitting laser diodes have been demonstrated. The threshold current density (for a cavity of 100 x 1000 mu m(2)) is 300, 300, 400 and 940 A/cm(2) for single, double, triple and quadruple QW lasers, respectively. The maximum 3 dB bandwidth reaches 17 GHz and high-speed transmission at 10 Gb/s up to 110 degrees C under a constant voltage has been demonstrated.

Keywords
Dilute nitride, 1.3 mu m, GaInNAs, GaAs, Laser
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-17742 (URN)10.1016/j.mejo.2008.06.013 (DOI)
Available from: 2009-04-18 Created: 2009-04-17 Last updated: 2009-04-18
Yang, L.-L., Zhao, Q., Willander, M. & Yang, J. (2009). Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition. Journal of Crystal Growth, 311(4), 1046-1050
Open this publication in new window or tab >>Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition
2009 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 4, p. 1046-1050Article in journal (Refereed) Published
Abstract [en]

The diameter of well-aligned ZnO nanorod arrays (ZNAs) grown on Si substrates has been well controlled from 150nm to 40nm by two-step chemical bath deposition method (CBD), i.e. substrate pretreatment with spin coating to form ZnO nanoparticles seed layer and CBD growth. The effects of ZnO nanoparticles density and diameter on size and alignment of ZNAs were investigated in detail by atomic force microscope (AFM), X-ray diffraction (XRD), scan electronic microscope (SEM), transmission electron microscope (TEM) and photoluminescence (PL). The results indicate that both diameter and density of ZnO nanoparticles which were pre-coated on the substrates will influence the size and alignment of ZNAs, but the density will play a key role to determine the diameter of ZNAs when the density is higher than the value of 2.3×108cm-2. Moreover, only a strong UV peak at 385 nm appears in room temperature PL spectrum for these samples, which indicates that  as-synthesized ZnO nanorods have a perfect crystallization and low density of deep level defects.

Keywords
ZnO nanorods arrays, CBD, Size-controlled growth
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-15533 (URN)10.1016/j.jcrysgro.2008.12.028 (DOI)
Note
Original Publication: Li-Li Yang, Qingxiang Zhao, Magnus Willander and J.H. Yang, Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition, 2009, Journal of Crystal Growth, (311), 4, 1046-1050. http://dx.doi.org/10.1016/j.jcrysgro.2008.12.028 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2008-11-14 Created: 2008-11-14 Last updated: 2017-12-14
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