K. L. Teo

Nanjing University, Nan-ching, Jiangsu Sheng, China

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Publications (58)133.64 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A spin-related photocurrent with swirly distribution and anomalous dependence of the total spin-related photocurrent on the incident angle were observed on spin-polarized two-dimensional gas in a Mg0.2Zn0.8O/ZnO heterostructure under illumination of circular polarized light at room temperature. The ferromagnetic two-dimensional Rashba model was adopted to interpret the results. It is demonstrated that a radial spin current induced by the gradient of the spin-polarized electron density is the origin of the anomalousness. This spin current only exists in spin polarized systems.
    Applied Physics Letters 05/2013; 102(19). · 3.79 Impact Factor
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    ABSTRACT: In this study, the origin and transport properties of high mobility carriers of two-dimensional electron gas (2DEG) at ZnMgO/ZnO interface have been investigated. It is found that the observed experimental dependence of carrier sheet density of 2DEG on ZnMgO thickness and Mg composition exhibits an excellent agreement with the theoretical calculations based on the surface charge model. It indicates that the mobile electrons in 2DEG are originated from the donor-like surface states. Moreover, the anomalous periodicity of Shubnikov-de Haas oscillations has been observed and the partial spin polarization feature of 2DEG has also been demonstrated, which exhibits the promising development in oxide spintronics applications. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 01/2013; 10(10):1268-1271.
  • K. Zheng, X.W. Sun, K.L. Teo
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    ABSTRACT: We report a unidirectional bipolar resistive switching in an n-type GaOx/p-type NiOx heterojunction fabricated by magnetron sputtering at room temperature. The resistive switching (RS) of the heterojunction directly relate with the concentration of intrinsic defects in oxide, such as oxygen vacancies and oxygen ions. Under external electric field, these electromigrated defects accumulate at the pn junction interface and modify the interface barrier, forming or rupturing the filamentary paths between n-GaOx and p-NiOx, leading to the switching between Ohmic and diode characteristics of the device.
    Nanoelectronics Conference (INEC), 2013 IEEE 5th International; 01/2013
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    ABSTRACT: We report a unidirectional bipolar resistive switching in an n-type GaOx/p-type NiOx heterojunction fabricated by magnetron sputtering at room temperature. The resistive switching behavior coincides with the switching between Ohmic conduction (low resistance) and rectifying behavior (high resistance) of the heterojunction diode. Under external electric field, electromigrated intrinsic defects, such as oxygen vacancies and oxygen ions, accumulate at the pn junction interface and modify the interface barrier, forming or rupturing the filamentary paths between n-GaOx and p-NiOx, leading to the switching between Ohmic and diode characteristics of the device. The device shows good endurance, retention performance, and scaling capability, signaling the potential of a diode-structured resistive switching device for non-volatile memory applications.
    Applied Physics Letters 10/2012; 101(14). · 3.79 Impact Factor
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    ABSTRACT: Quantum transport properties of two-dimensional electron gas (2DEG) in undoped MgxZn1−xO/ZnO heterostructures grown by metal organic vapor phase epitaxy have been investigated. A large zero-field spin-splitting energy more than 15 meV in the 2DEG is determined at 1.6 K. Meanwhile, ferromagnetism is observed in the heterostructures. The findings reveal that the 2DEG is spin polarized at zero magnetic fields. It is believed that the exchange interaction between the itinerant electrons in the two-dimensional channel and the magnetic polarons in the MgxZn1−xO barrier around the interface results in the spin polarization of the 2DEG.
    Applied Physics Letters 05/2012; 100(19). · 3.79 Impact Factor
  • Applied Physics Letters 01/2012; 101(14):143110-5. · 3.79 Impact Factor
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    ABSTRACT: Magneto-transport studies on ZnMgO/ZnO heterostructures grown by MOVPE technique have been performed. The features of spin-polarization of 2DEG and intrinsic ferromagnetism of heterostructure were observed at 1.5 K and the related physical mechanisms are discussed.
    Optoelectronic and Microelectronic Materials & Devices (COMMAD), 2012 Conference on; 01/2012
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    ABSTRACT: We report on the high mobility wide electron slabs with enhanced correlation effects by tailoring the polarization effects in a functionally graded ZnMgO/ZnO heterostructures. The characteristics of three-dimensional (3D) spreading electrons are evidenced by the capacitance-voltage profiling and the quantization of 3D Fermi surface in magneto-transport measurements. Despite the weak spin-orbit interaction, such electron slabs are spin-polarized with a large zero-field spin splitting energy, which is induced by the carrier-mediated ferromagnetism. Our results suggest that the vast majority of electrons are localized at the surface magnetic moment which does not allow spin manipulations, and only in the region visited by the itinerant carriers that the ferromagnetic exchange interactions via coupling to the surface local moments contribute to the spin transport. The host ferromagnetism is likely due to the formation of Zn cation vacancies on the surface regime induced by the stabilization mechanism and strain-relaxation in ZnMgO polar ionic surface.
    Scientific Reports 01/2012; 2:533. · 2.93 Impact Factor
  • S. T. Lim, J. F. Bi, Lu Hui, K. L. Teo
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    ABSTRACT: We present the magnetotransport studies of Ge1−xMnxTe ferromagnetic semiconductor under hydrostatic pressure. The investigation of the normal and Hall resistivities provide an insight to the dependence of carrier concentration, mobility, and magnetic properties on pressure. Our results reveal that the application of pressure changes the band structure, which can be explained by a two valence band model. We observe the enhancement and reduction of Curie temperature within a pressure range of 0–24 kbar. Analysis within the framework of the Ruderman–Kittel–Kasuya–Yosida model allows us to identify the factors in controlling the Tc, in which the exchange interaction plays a predominant role in the formation of ferromagnetic phase.
    Journal of Applied Physics 07/2011; 110(2). · 2.21 Impact Factor
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    ABSTRACT: We report an indium-free transparent resistive switching random access memory device based on GZO-Ga<sub>2</sub>O<sub>3</sub>-ZnO-Ga<sub>2</sub>O<sub>3</sub> -GZO structure by metal-organic chemical vapor deposition. The memory device shows good transmittance in the visible region and bipolar resistive switching behavior with good cycling characteristics and retention time under room temperature. The conduction and resistive switching mechanism was discussed based on filament theory.
    IEEE Electron Device Letters 07/2011; · 2.79 Impact Factor
  • S. T. Lim, J. F. Bi, K. L. Teo, T. Liew
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    ABSTRACT: We have investigated the magnetic and magnetotransport properties of Ge1-xMnxTe (x = 0.1) grown by molecular-beam epitaxy. Our results show that the sample exhibits two ferromagnetic transition temperatures at TC = 34 K and TC* = 100 K. We infer that Tc is a long-range ferromagnetic ordering in view of sufficient carriers generating uniform ferromagnetism, whereas TC* is a short-range ferromagnetic ordering due to ferromagnetic clusters. The temperature dependence of the resistivity ρ(T) curve exhibits a shallow minimum near TC. The upturn of ρ(T) toward the low temperature (T < TC) is well described by a weak-localization model, whereas in the high-temperature regime (T > TC), the phonon scattering dominates.
    Journal of Applied Physics 03/2011; 109(7):07C314-07C314-3. · 2.21 Impact Factor
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    ABSTRACT: We report the formation of two-dimensional electron gas (2DEG) at the Zn1−xMgxO/ZnO interface grown by metal-organic vapor phase epitaxy on sapphire substrates. The existence of the 2DEG is confirmed by the observation of Shubnikov–de Haas oscillations and the integer quantum Hall effect. In particular, the Zn0.8Mg0.2O/ZnO heterostructure shows a high Hall mobility of 2138 cm2/V s with a carrier sheet density of 3.51×1012 cm−2 at 1.4 K. We attribute the origin of 2DEG to be the donor states on ZnMgO surface. The dependence of carrier sheet density of 2DEG on ZnMgO layer thickness and Mg composition (x) are also investigated.
    Applied Physics Letters 09/2010; 97(11):111908-111908-3. · 3.79 Impact Factor
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    ABSTRACT: We report the antiferromagnetic (AFM) thickness dependence study of zinc-blende CrTe/ZnTe/MnTe layered structure grown on GaAs (100) by low temperature molecular beam epitaxy. The coercivity (H<sub>C</sub>) and exchange bias field (H<sub>E</sub>) show a nonmonotonic dependence on the AFM thickness. Both (H<sub>C</sub>) and H<sub>E</sub> exhibit a maximum value at the AFM thickness of ∼15 nm . With decreasing AFM thickness, we found that the blocking temperature drops from 70 (Néel temperature of bulk MnTe) to 22 K, while the Curie temperature is found to increase from 100 to 190 K. Additionally, a vertical magnetization shift is observed in the M-H loop, which can be attributed to the presence of frozen ferromagnetic spins at the interface.
    Journal of Applied Physics 06/2010; · 2.21 Impact Factor
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    ABSTRACT: We present the results on the exchange coupling in the zinc-blende CrTe/spacer/MnTe structure with ZnTe acting as a spacer layer (SL). The magnetic hysteresis (M-H) loops show significant shifts in both horizontal and vertical directions. A nonmonotonic variation of the exchange bias field (H<sub>E</sub>) and coercivity (H<sub>C</sub>) with the SL thickness is observed. The Curie temperature decreases as the SL thickness increases. The maximum of H<sub>E</sub> and H<sub>C</sub> values occur at a SL thickness of 12 ML (monolayer). Strikingly, the exchange coupling remains noticeable even the thickness of SL reaches 24 ML. The exchange bias field and vertical shift are discussed on the basis of frozen ferromagnetic moment model.
    Journal of Applied Physics 06/2010; · 2.21 Impact Factor
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    ABSTRACT: n -ZnO/ n -GaAs heterostructured light-emitting diodes have been fabricated by a low-cost ultrasonic spray pyrolysis technique. Nanoscale interface analysis was carried out with scanning transmission electron microscopy. An ~ 8.6-nm-thick amorphous GaAsZnInO was found in the n -ZnO/ n -GaAs interface. A strong and broad white electroluminescence band centered at ~ 525 nm and a weak near-infrared emission peaked at ~ 815 nm were observed when n -GaAs was positively biased. The 815-nm emission is believed to be related to the interface layer, and the 525-nm emission is assigned to the recombination of electrons from conduction band to deep-level holes in the ZnO layer.
    IEEE Transactions on Electron Devices 02/2010; · 2.06 Impact Factor
  • J. D. Ye, G. Q. Lo, S. L. Gu, K. L. Teo
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    ABSTRACT: In this work, we demonstrate the layer-by-layer epitaxy of Mg-composition graded ZnMgO/ZnO heterostructure on sapphire substrate by MOVPE technique. The polarization field tailored by the graded heterostructure induces wide electron slabs with high mobility at low temperature. The transport properties and mechanisms have been discussed in details.
    01/2010;
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    ABSTRACT: The effect of arsenic doping on the growth kinetics of ZnO during metalorganic vapor phase epitaxy has been investigated. Arsenic was found to segregate to the growth surface and facilitate layer-by-layer growth. Such surfactant enhances the lateral expansion of the terraces preferential along [20] direction and also reduces the screw lattice distortion. Arsenic is expected to reduce the total surface energy and diffusion barrier of oxygen adatoms, hence producing Zn-rich surface condition on the growth front, in which two-dimensional growth is thermodynamically and kinetically favored. The origin of tiny hexagonal pits formed on the wide terrace is discussed in terms of the modified step-bunching mechanism.
    Applied Physics Letters 09/2009; 95(10):101905-101905-3. · 3.79 Impact Factor
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    ABSTRACT: We utilize the effect of hydrostatic pressure to investigate the magnetotransport properties of degenerate p-Ge1−xMnxTe (x = 0.10) ferromagnetic semiconductor. The Curie temperature was found to increase with pressure as 0.27 K/kbar, which can be understood on the basis of the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction mechanism. For sufficiently high carrier concentration of po ∼ 1021 cm−3, both the light holes from the L valence band and the heavy holes from the Σ valence band contribute to the RKKY interaction. Additionally, a negative magnetoresistance is observed at low temperature and is found to decrease with pressure.
    Applied Physics Letters 08/2009; 95(7):072510-072510-3. · 3.79 Impact Factor
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    ABSTRACT: We have studied the exchange bias at the ferromagnetic (FM)/antiferromagnetic interface in the zinc-blende transition-metal chalcogenides, CrTe (5 nm)/MnTe(40 nm) bilayer grown on GaAs (100) substrate by molecular-beam epitaxy. A negative exchange bias shift in the hysteresis loop is observed when the bilayer is cooled in the applied magnetic field. The temperature-dependent remanent magnetization shows a clear enhancement of the Curie temperature and magnetization in the bilayer as compared to a single FM layer. The effects of temperature, cooling field, and angular dependence on the exchange bias have been investigated.
    Applied Physics Letters 06/2009; 94(25):252504-252504-3. · 3.79 Impact Factor
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    ABSTRACT: In this letter, using both off-resonant and resonant Raman spectroscopic techniques, the correlation of optical phonons and structural disorder in As+ implanted ZnO single crystals has been investigated. An additional broad peak shoulder at 550 cm−1 between the transverse optical and longitudinal optical (LO) phonons was clarified to be resonant Fro¨hlich optical phonon mode in the framework of effective dielectric function. Under resonance condition, an asymmetric broadening and softening of the LO phonon along with a blueshifted luminescent peak revealed the decreasing phonon coherent length and nanocrystallization with increasing fluence, respectively, in good agreement with the observations of transmission electron microscopy and atomic force microscopy.
    Applied Physics Letters 01/2009; 94(1). · 3.79 Impact Factor

Publication Stats

262 Citations
133.64 Total Impact Points

Institutions

  • 2012
    • Nanjing University
      Nan-ching, Jiangsu Sheng, China
  • 2011
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Singapore, Singapore
  • 2004–2010
    • National University of Singapore
      • Department of Electrical & Computer Engineering
      Singapore, Singapore