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Trinh, Xuan Thang
Alternative names
Publications (10 of 19) Show all publications
Zeglio, E., Vagin, M., Musumeci, C., Ajjan, F., Gabrielsson, R., Trinh, X. t., . . . Inganäs, O. (2015). Conjugated Polyelectrolyte Blends for Electrochromic and Electrochemical Transistor Devices. Chemistry of Materials, 27(18), 6385-6393
Open this publication in new window or tab >>Conjugated Polyelectrolyte Blends for Electrochromic and Electrochemical Transistor Devices
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2015 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 18, p. 6385-6393Article in journal (Refereed) Published
Abstract [en]

Two self-doped conjugated polyelectrolytes, having semiconducting and metallic behaviors, respectively, have been blended from aqueous solutions in order to produce materials with enhanced optical and electrical properties. The intimate blend of two anionic conjugated polyelectrolytes combine the electrical and optical properties of these, and can be tuned by blend stoichiometry. In situ conductance measurements have been done during doping of the blends, while UV vis and EPR spectroelectrochemistry allowed the study of the nature of the involved redox species. We have constructed an accumulation/depletion mode organic electrochemical transistor whose characteristics can be tuned by balancing the stoichiometry of the active material.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2015
National Category
Materials Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-122212 (URN)10.1021/acs.chemmater.5b02501 (DOI)000361935000028 ()
Note

Funding Agencies|Marie Curie network "Renaissance"; Knut and Alice Wallenberg foundation through Wallenberg Scholar grant; Swedish Research Council [VR-2014-3079, D0556101]; Carl Trygger Foundation [CTS 12:206]

Available from: 2015-10-26 Created: 2015-10-23 Last updated: 2017-12-01
Trinh, X. T., Ivády, V., Kawahara, K., Suda, J., Kimoto, T., Gali, Á., . . . Son, N. T. (2015). Electron paramagnetic resonance studies of carbon interstitial related defects in 4H-SiC.
Open this publication in new window or tab >>Electron paramagnetic resonance studies of carbon interstitial related defects in 4H-SiC
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

In n-type 4H-SiC grown by chemical vapor deposition and irradiated by low-energy (250 keV) electrons, an electron paramagnetic resonance center, labeled EI8a, was observed at room temperature. A short anneal at temperatures in the range of 300-500 °C in darkness changes EI8a to a new center, labeled EI8b, which can be converted back by illumination at room temperature. We show that EI8a and EI8b are the two different configurations of the same defect, labeled EI8, with C1h symmetry and an electron spin S=1/2. The EI8 center is stable up to ~650 °C and annealed out at ~800 °C. Based on the observed hyperfine structures due to the hyperfine interaction between the electron spin and the nuclear spins of four 29Si atoms and three 13C atoms, the EI8 center is suggested to be related to a carbon interstitial cluster.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-117880 (URN)
Available from: 2015-05-12 Created: 2015-05-12 Last updated: 2015-05-12Bibliographically approved
Trinh, X. T. (2015). Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Electron Paramagnetic Resonance Studies of Point Defects in AlGaN and SiC
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Point defects in semiconductor materials are known to have important influence on the performance of electronic devices. For defect control, knowledge on the model of defects and their properties is required. Information on defects, such as the symmetry and the localization of spins, is essential for identification of defects and understanding their electronic structure. Such information can be obtained from Electron Paramagnetic Resonance (EPR). In many cases, the energy levels of defects can be determined from photoexcitation EPR (photo-EPR) or temperature dependence of the EPR signal. The thesis contains six papers, focusing on the identification and electronic structure investigation of defects and impurities in AlxGa1-xN (x~0.7-1) and silicon carbide (SiC) using EPR in combination with other electrical characterizations and density functional theory calculations.

The two first papers concern EPR studies of silicon (Si) in AlGaN alloys. Due to its direct and wide band gap which can be tailored from 3.4 eV for GaN to 6.2 eV for AlN, high-Al-content wurtzite AlxGa1-xN (x≥0.7) has been considered as a promising material for fabrication of compact, high-efficiency and non-toxic deep ultraviolet light-emitting diodes (LEDs) and laser diodes (LDs) for replacing low-efficiency and toxic mercury lamps in water/air purification and sterilization. Si is commonly used for n-type doping in AlGaN and AlN, but the conductivity of Si-doped AlxGa1-xN was often reported to drop abruptly at high Al content (x>0.7) and the reason was often speculated to be due to either carrier compensation by other deep levels or Si itself when it transforms from a shallow donor to a DX (or negative-U) center which acts as an acceptor. In paper 1, we showed that Si already forms a stable DX center in AlxGa1-xN with x ~0.77. However, with the Fermi level locating only ~3 meV below the neutral charge state, Ed, Si still behaves as a shallow donor. Negligible carrier compensation by oxygen (O) in Al0.77Ga0.23N:Si layers was observed, suggesting that at such Al content, O does not seem to hinder the n-type doping in the material. In paper 2, we found the coexistence of two Si DX centers, the stable DX1 and the metastable DX2, in AlxGa1-xN for x≥0.84. For the stable DX1 center, abrupt deepening of the energy level of the negative charge state DX, EDX, which determines the ionization energy Ea of the Si donor, with increasing of the Al content for x≥0.83 was observed. The dependence of Ea on the Al content in AlxGa1-xN:Si layers (0.79≤x≤1) was determined. The results explain the drastic decrease of the conductivity as often reported for  AlxGa1-xN:Si in previous transport studies. For the metastable DX2 center, we found that the EDX level remains close to Ed for x=0.84÷1.

SiC is a wide band-gap semiconductor having high-thermal conductivity, high breakdown field, and large saturated electron drift velocity which are essential properties for high-voltage and high-power devices. In paper 3, the identification of niobium (Nb) in 4Hand 6H-SiC grown by high-temperature chemical vapor deposition (CVD) by EPR and theoretical calculations is presented. We showed that the incorporated Nb formed asymmetric split-vacancy defect (NbSiVC) in which Nb locates in a divacancy, closer to the Si vacancy, and prefers only the hexagonal-hexagonal configuration. In papers 4 and 5, we present the identification and the electronic structure of the negative-U Z1/Z2 center in 4HSiC. The Z1/Z2 defect is known to be the most common deep level revealed by Deep Level Transient Spectroscopy (DLTS) in 4H-SiC epitaxial layers grown by CVD. The center is also known to be the lifetime killer in as-grown CVD material and, therefore, attracts much attention. Using high-doped n-type free-standing 4H-SiC layers irradiated with low-energy (250 keV) electrons, which mainly displace carbon atoms creating C vacancies (VC), C interstitials and their associated defects, it was possible to increase the irradiation dose and, hence, the defect concentration, allowing the application of EPR and DLTS on the same samples. In paper 4, using EPR, photo-EPR, DLTS and capacitance-voltage measurements, we showed that the Z1/Z2 center is related to the (2-|0) level of VC and its higher-lying levels Z1 and Z2 are related to the (-|0) levels of VC at the hexagonal (h) and quasi-cubic (k) sites, respectively. In paper 5, combining EPR and supercell calculations, the negatively charged VC at the k-site was identified. We obtained the excellent agreement in the energy levels of Z1/Z2 determined by DLTS and energy levels of VC calculated by supercell calculations and observed clear negative-U behaviors of the negatively charged VC at both k and h-sites by EPR measurements, consolidating our assignment of the Z1/Z2 levels to the negatively charged states of VC. In paper 6, we studied a defect related to displaced C atoms in n-type 4H-SiC irradiated by low-energy electrons. In irradiated layers, we observed an EPR center at room temperature. After annealing at temperatures in the range of 300-500 °C, this center transforms to a second configuration which is observed in darkness and can be  changed back to the first configuration under illumination. Based on the observed 29Si and 13C hyperfine structures, two observed configurations of the EPR center were suggested to be related to different configurations of a carbon interstitial cluster. The annealing, bistable behaviors and energy levels of this EPR center are discussed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. p. 36
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1670
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-117882 (URN)10.3384/diss.diva-117882 (DOI)978-91-7519-064-8 (ISBN)
Public defence
2015-06-02, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-05-12 Created: 2015-05-12 Last updated: 2019-11-15Bibliographically approved
Nilsson, D., Trinh, X. T., Janzén, E., Son, T. N. & Kakanakova-Georgieva, A. (2015). On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers. Physica status solidi. B, Basic research, 252(6), 1306-1310
Open this publication in new window or tab >>On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers
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2015 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 6, p. 1306-1310Article in journal (Refereed) Published
Abstract [en]

We have studied the silicon donor behavior in intentionally silicon doped AlxGa1-xN (0.63≤x≤1) grown by hot-wall metal-organic chemical vapor deposition. Efficient silicon doping was obtained for lower Al contents whereas the conductivity drastically reduces for AlGaN layers with Al content in the range x~0.84-1. Degradation of the structural quality and compensation by residual O and C impurities were ruled out as possible explanations for the reduced conductivity. By combining frequency dependent capacitance-voltage and electron paramagnetic resonance measurements we show that the Si donors are electrically active and that the reduced conductivity can be explained by the increased activation energy caused by the sharp deepening of the Si DX state..

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2015
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106725 (URN)10.1002/pssb.201451559 (DOI)000355756200016 ()
Note

Swedish Research Council (VR); VR Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM); Swedish Energy Agency; Knut and Alice Wallenberg Foundation (KAW); Swedish Governmental Agency for Innovation Systems (VINNOVA)

Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2017-12-05Bibliographically approved
Szállás, A., Szász, K., Trinh, X. T., Son, N. T., Janzén, E. & Gali, A. (2014). Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory. Journal of Applied Physics, 116(11), 113702-1-113702-5
Open this publication in new window or tab >>Characterization of the nitrogen split interstitial defect in wurtzite aluminum nitride using density functional theory
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2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 11, p. 113702-1-113702-5Article in journal (Refereed) Published
Abstract [en]

We carried out Heyd-Scuseria-Ernzerhof hybrid density functional theory plane wave supercell calculations in wurtzite aluminum nitride in order to characterize the geometry, formation energies, transition levels, and hyperfine tensors of the nitrogen split interstitial defect. The calculated hyperfine tensors may provide useful fingerprint of this defect for electron paramagnetic resonance measurement.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-112057 (URN)10.1063/1.4895843 (DOI)000342837000020 ()
Note

Funding Agencies|MTA Lendulet program of the Hungarian Academy of Sciences; Swedish Energy Agency; Swedish Foundation for Strategic Research (SSF); Knut and Alice Wallenberg Foundation; National Supercomputer Center in Sweden [SNIC 2013-1-331]; National Information Infrastructure Development Institute in Hungary

Available from: 2014-11-17 Created: 2014-11-13 Last updated: 2017-12-05Bibliographically approved
Trinh, X. T. (2014). Electron Paramagnetic Resonance studies of negative-U centers in AlGaN and SiC. (Licentiate dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Electron Paramagnetic Resonance studies of negative-U centers in AlGaN and SiC
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon (Si) is the most commonly used n-type dopant in AlGaN, but the conductivity of Si-doped AlxGa1-xN was often reported to drop abruptly at high Al content (x>0.7) and the reason was often speculated to be due to either compensation by deep levels or self-compensation of the so-called DX (or negative-U) center. Understanding the electronic structure of Si and carrier compensation processes is the essential for improving the n-type doping of high-Al-content AlxGa1-xN. In our studies of Si-doped AlGaN layers grown by metal-organic chemical vapor deposition, Electron Paramagnetic Resonance (EPR) was used to study the electronic structure of Si in high-Al-content AlxGa1-xN.

From the temperature dependence of the concentration of the Si donor on the neutral charge state Ed determined by EPR, we showed that Si already forms a stable DX center in AlxGa1-xN with x ~0.77. However, with the Fermi level locating only ~3 meV below Ed, Si still behaves as a shallow donor and high conductivity at room temperature could be achieved in Al0.77Ga0.23N:Si layers. In samples with the concentration of the residual oxygen (O) impurity larger than that of Si, we observed no carrier compensation by O in Al0.77Ga0.23N:Si layers, suggesting that at such Al content, O does not seem to hinder the n-type doping in the material. The result is presented in paper 1.

In paper 2, we determined the dependence of the EDX level of Si on the Al content in AlxGa1-xN:Si layers (0.79≤x≤1) with the Si concentration of ~2×1018 cm-3 and the concentrations of residual O and C impurities of about an order of magnitude lower (~1÷2×1017 cm-3). We found the coexistence of two DX centers (stable and metastable ones) of Si in AlxGa1-xN for x≥0.84. For the stable DX center, abruptly deepening of EDX with increasing of the Al content for x≥0.83 was observed, explaining the drastic decrease of the conductivity as often reported in previous transport studies. For the metastable DX center, the EDX level remains close to Ed for x=0.84÷1 (~11 meV for AlN).

The Z1/Z2 defect is the most common deep level revealed by Deep Level Transient Spectroscopy (DLTS) in 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD). It has previously been shown by DLTS to be a negative-U system which is more stable with capturing two electrons. The center is also known to be the lifetime killer in asgrown CVD material and, therefore, attracts much attention. Despite nearly two decades of intensive studies, including theoretical calculations and different experimental techniques, the origin of the Z1/Z2 center remains unclear. EPR is known to be a powerful method for defect identification, but a direct correlation between EPR and DLTS is difficult due to different requirements on samples for each technique. Using high n-type 4H-SiC CVD free-standing layers irradiated with lowenergy (250 keV) electrons, which mainly displace carbon atoms creating C vacancies, C interstitials and their associated defects, it was possible to increase the irradiation dose, allowing the application of EPR and DLTS on the same samples. Combining EPR, DLTS and supercell calculations, we identified the negatively charged carbon vacancy at the quasi-cubic (k) site and observed clear negative-U behaviors of the negative carbon vacancies at both hexagonal (h) and k sites. Our results showed that the Z1/Z2 center is related to the (2-|0) level of VC and its higher-lying levels Z1 and Z2 are related to the (-|0) levels of VC at the h and k sites, respectively. The result is presented in paper 3.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. p. 28
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1697
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112408 (URN)10.3384/lic.diva-112408 (DOI)978-91-7519-168-3 (ISBN)
Presentation
2014-12-16, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-11-25 Created: 2014-11-25 Last updated: 2015-04-17Bibliographically approved
Nilsson, D., Trinh, X. T., Son, T. N., Janzén, E., Sahonta, S.-L., Kappers, M. J., . . . Kakanakova-Georgieva, A. (2014). Highly Si-doped Al0.72Ga0.28N layers: n-type conductivity bound by the process temperature.
Open this publication in new window or tab >>Highly Si-doped Al0.72Ga0.28N layers: n-type conductivity bound by the process temperature
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Establishing n- and p- type conductivity via intentional doping in epitaxial layers is fundamental to any semiconductor material system and its relevant device applications. Process parameters such as temperature, precursor gas-flow-rates and pressure may all control intentional doping in metal-organic chemical vapour deposition (MOCVD) of semiconductor materials. The incorporation of impurities such as carbon and oxygen may also be affected by the same process parameters, and the concentration of these impurities has a direct impact on the electrical, optical and thermal properties of epitaxial layers, as has been observed in the MOCVD of technologically-important III-V semiconductor materials such as AlGaAs and GaN.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-106724 (URN)
Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2014-05-20Bibliographically approved
Trinh, X. T., Szasz, K., Hornos, T., Kawahara, K., Suda, J., Kimoto, T., . . . Son, N. T. (2014). Identification of the negative carbon vacancy at quasi-cubic site in 4H-SiC by EPR and theoretical calculations. In: Silicon Carbide and Related Materials 2013, PTS 1 AND 2: . Paper presented at 15th International Conference on Silicon Carbide and Related Materials (ICSCRM 2013), 29 September - 4 October 2013, Miyazaki, Japan (pp. 285-288). Trans Tech Publications Inc., 778-780
Open this publication in new window or tab >>Identification of the negative carbon vacancy at quasi-cubic site in 4H-SiC by EPR and theoretical calculations
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2014 (English)In: Silicon Carbide and Related Materials 2013, PTS 1 AND 2, Trans Tech Publications Inc., 2014, Vol. 778-780, p. 285-288Conference paper, Published paper (Refereed)
Abstract [en]

In freestanding n-type 4H-SiC epilayers irradiated with low-energy (250 keV) electrons at room temperature, the electron paramagnetic resonance (EPR) spectrum of the negative carbon vacancy at the hexagonal site, V-C(-)(h), and a new signal were observed. From the similarity in defect formation and the spin-Hamiltonian parameters of the two defects, the new center is suggested to be the negative C vacancy at the quasi-cubic site, V-C(-)(k). The identification is further supported by hyperfine calculations.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014
Series
Materials Science Forum, ISSN 1662-9752 ; 778-780
Keywords
Carbon vacancy; negative-U behavior; electron irradiation; EPR; supercell calculations
National Category
Ceramics
Identifiers
urn:nbn:se:liu:diva-108197 (URN)10.4028/www.scientific.net/MSF.778-780.285 (DOI)000336634100067 ()
Conference
15th International Conference on Silicon Carbide and Related Materials (ICSCRM 2013), 29 September - 4 October 2013, Miyazaki, Japan
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2014-10-28Bibliographically approved
Kawahara, K., Trinh, X. T., Son, N. T., Janzén, E., Suda, J. & Kimoto, T. (2014). Quantitative comparison between Z1∕2 center and carbon vacancy in 4H-SiC. Journal of Applied Physics, 115(14), 143705
Open this publication in new window or tab >>Quantitative comparison between Z1∕2 center and carbon vacancy in 4H-SiC
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2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 14, p. 143705-Article in journal (Refereed) Published
Abstract [en]

In this study, to reveal the origin of the Z(1/2) center, a lifetime killer in n-type 4H-SiC, the concentrations of the Z(1/2) center and point defects are compared in the same samples, using deep level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). The Z(1/2) concentration in the samples is varied by irradiation with 250 keV electrons with various fluences. The concentration of a single carbon vacancy (V-C) measured by EPR under light illumination can well be explained with the Z(1/2) concentration derived from C-V and DLTS irrespective of the doping concentration and the electron fluence, indicating that the Z(1/2) center originates from a single V-C.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-106850 (URN)10.1063/1.4871076 (DOI)000334680400031 ()
Available from: 2014-05-28 Created: 2014-05-23 Last updated: 2017-12-05Bibliographically approved
Kakanakova-Gueorguie, A., Nilsson, D., Trinh, X. T., Son, N. T. & Janzén, E. (2014). Silicon and oxygen in high-Al-content AlGaN: incorporation kinetics and electron paramagnetic resonance study. In: Gettering and Defect Engineering in Semiconductor Technology XV: . Paper presented at 15th International Conference on Gettering and Defect Engineering in Semiconductor Technology (GADEST), 22- 27 September, 2013, Oxford, ENGLAND (pp. 441-445). Trans Tech Publications Inc., 205-206
Open this publication in new window or tab >>Silicon and oxygen in high-Al-content AlGaN: incorporation kinetics and electron paramagnetic resonance study
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2014 (English)In: Gettering and Defect Engineering in Semiconductor Technology XV, Trans Tech Publications Inc., 2014, Vol. 205-206, p. 441-445Conference paper, Published paper (Refereed)
Abstract [en]

The high-Al-content AlxGa1-xN alloys, xgreater than0.70, and AlN is the fundamental wide-band-gap material system associated with the technology development of solid-state LEDs operating at the short wavelengths in the deep-UV (lambda less than 280 nm). Yet, their properties are insufficiently understood. The present study is intended to bring elucidation on the long-time debated and much speculated Si transition from shallow donor in GaN to a localized deep DX defect in AlxGa1-xN alloys with increasing Al content. For that purpose electron paramagnetic resonance is performed on a particular selection of high-Al-content epitaxial layers of Al0.77Ga0.23N, alternatively Al0.72Ga0.28N, alloy composition.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014
Series
Solid State Phenomena, ISSN 1662-9779 ; 205-206
Keywords
AlGaN; MOCVD; Si doping; electron paramagnetic resonance
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-108182 (URN)10.4028/www.scientific.net/SSP.205-206.441 (DOI)000336338000065 ()
Conference
15th International Conference on Gettering and Defect Engineering in Semiconductor Technology (GADEST), 22- 27 September, 2013, Oxford, ENGLAND
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2014-08-21Bibliographically approved
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