에어로졸 CVD를 이용한 성분기울기 ZnMgO 나노복합박막의 증착과 구조분석

윤종걸 水原大學校 2016 論文集 Vol.30 No.-

Compositionally graded ZnMgO films are deposited on platinized Si substrates at 420℃ using aerosol-assisted chemical vapor deposition at a slightly lower pressure than atmospheric pressure. The principle and method of depositing the compositionally graded ZnMgO films are described. The structure and composition of the films are analysed by using x-ray diffraction and second ion mass spectroscopy, respectively. The results show that the c-axis lattice constant of the films is continuously decreasing and the ratio of Mg/Zn increases along the direction toward the film surface. Since the increase in Mg content in the ZnMgO film causes changes in energy band gap, the graded-composition should result in the graded-band gap. Current-voltage measurements for the graded films show highly rectifying characteristics of the films, revealing that asymmetric electronic structure is achieved in the film by the graded-band gap. This study provides a basic understanding of the properties of compositionally graded ZnMgO for the development of ZnO-based oxide electronic devices.

Charge Transfer at the Interfaces of Polycrystaline ZnO/Zn1-xMgxO/ZnO Heterostructures

윤종걸,Kyoung Ok Jung,Hong Joon Kim,김경섭 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.4

Charge transfer at the interfaces of polycrystalline ZnO/Zn1-xMgxO(ZnMgO)/ZnO heterostructures, which were grown on glass substrates by using ultrasonic spray pyrolysis, were investigated by measuring the electrical and the optical properties of the heterostructures. Spectral blue shifts of optical band gap were observed for ZnO/ZnMgO/ZnO heterostructures and were analyzed in terms of Burstein-Moss and band-gap-renormalization effects to estimate the amount of charge transfer. Compared to a single-layer Al-doped ZnO (ZnO:Al) films, the electrical properties of the ZnO:Al/ZnMgO/ZnO:Al heterostructure were found to be enhanced with increasing electron mo- bility by a factor of 1.6. Even in these polycrystalline heterostructures, the conduction band offset between ZnMgO and ZnO:Al can cause electron transfer at the interface and decrease the energy barrier at the grain boundaries, resulting in an enhanced of mobility.

Structural Characteristics of Sputter-Deposited Pb(Zr,Ti)O3/ZnO Heterostructure Films

윤종걸,Ya. I. Alivov,F. Agra,B. Xiao,S. Chevtchenko,H. Morkoc 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.4

The structural properties of PbZr0:52Ti0:48O3 (PZT)/ZnO heterostructure films deposited on sapphire substrates by rf-sputtering were investigated using X-ray diffraction and atomic force microscopy for various deposition and annealing temperatures. Pure perovskite PZT films with smooth surface morphologies could be obtained by depositing the films at 650 ℃ and subsequent oxygen annealing at the same temperature. The post-annealing in oxygen also enhanced both the (111) orientation of the PZT films and the pyrochlore-to-perovskite phase transformation. The structural symmetry at the interface of PZT/ZnO heterostructures is discussed in conjunction with the crystalline orientations of PZT film, which favors (111)- and (110)-orientations of PZT films on (0001) ZnO during growth and the subsequent annealing process.

에어로졸 CVD법으로 성장된 ZnMgO 박막의 전자적 결함상태

윤종걸 水原大學校 2019 論文集 Vol.33 No.-

에어로졸을 이용한 화학기상증착법으로 ZnMgO 박막을 420℃에서 c-sapphire 및 백금막이 증착된 실리콘 기판 (Pt/Si) 위에 성장시키고 x-선 회절을 통해 박막의 구조를 분석하였다. 성장된 박막은 모두 (0001) 방향으로 성장되 었으며, 특히 c-sapphire 기판에서는 에피박막이 성장됨을 확인할 수 있었다. 박막 내의 전자적 결함상태는 photoluminescence(PL)와 electroluminescence(EL) 측정을 통해 분석하였다. 특히 ZnMgO 박막에 대해서 전기장을 걸어 발생한 EL 스펙트럼은 PL 스펙트럼과 밀접한 상관성을 보여주고 있음을 확인하였다. 이로부터 박막 내에 존재 하는 Zn interstitial 및 산소 공공 등의 구조적 결함이 만드는 전자적 결합상태에 대해 논의하고 ZnMgO 박막에서 관측된 백색광 EL 원리를 이해할 수 있었다.

Impurity effects on the field-induced commensurate phase of thioura

Yoon,Jong-Gul 水原大學校 1991 論文集 Vol.9 No.-

불순물을 첨가한 thiourea 단결정에 대해 직류 전기장하에서의 유전상수를 측정함으로써, 전기장에 의해 유도된 1/8-맞맞음상(commensurate phase)에 대한 불순물 효과를 조사하였다. 불순물의 양이 증가할수록 불순물에 의한 pinning효과로 인해 상전이 온도 T8 부근에서의 열이력현상이 뚜렷하게 관측되었으며, 불순물의 양이 많이 들어간 시료에서는 어떤 임계 전기장 Ec가 존재하여 그 이하 크기의 전기장에서는 맞맞음상이 안정된 상태로 존재할 수 없을 것으로 보이는 결과를 얻었다. 이러한 결과로부터 변조 파수 벡터의 변화가 불순물에 의한 pinning효과에 의해 계단 형태로 변할 가능성에 대해 논의하였다. Dielectric constant measurements on urea-doped thiourea single crystals under field have been carried out to study the effects of impurities on the field-induced 1/8-commensurate phase. As the concentration of impurity is increased, a pronounced thermal hysteresis of the dielectric behaviour due to pinning effect is observed around T8. For the highly urea-doped thiourea crystals, there exists a critical field Ec below which no commensurate phase would stabilize under field in contrast to the pure crystal. It is discussed that stepwise variations in the modulation wave vector may occur due to the impurity pinning effect.

Nanoscale studies of defect-mediated polarization switching dynamics in ferroelectric thin film capacitors

양상모,윤종걸,노태원 한국물리학회 2011 Current Applied Physics Vol.11 No.5

Recent developments in ferroelectric (FE) domain imaging techniques have established an understanding of intriguing polarization switching dynamics. In particular, nanoscale studies of FE domain switching phenomena using piezoresponse force microscopy (PFM) can provide important microscopic details on nucleation and subsequent growth of domains, complementing conventional electrical measurements that only give macroscopic information. This review covers recent nanoscale PFM studies of domain switching dynamics in FE thin films. Recent nanoscale PFM-based studies have demonstrated that quenched defects inside the FE thin films play important roles in domain switching processes, including defect-mediated inhomogeneous nucleation, pinning-dominated nonlinear dynamics of domain walls,and many other intriguing phenomena.

Optical Characterization of Superconducting Strip Photon Detector Using MgB₂

H. Shibata,심규환,강석일,윤종걸,최우석 한국초전도학회 2012 Progress in superconductivity Vol.14 No.2

Bias current dependence of a superconducting strip photon detector is studied in the wavelength range of 405 to 1310 nm. The detector is made of an MgB2 meander pattern with the line width of 135 nm and thickness of 10 nm. At 1310 nm, the detection efficiency exponentially decreases as the bias current decreases. While at 405 nm, the detection efficiency almost saturates in the high bias current region. These features suggest that the intrinsic detection efficiency of the MgB2 detector is high at 405 nm.

Scaling Behavior of Amplitude-dependent Ferroelectric Hysteresis Loops in an Epitaxial PbZr_(0.2)Ti_(0.8O3) Thin Film

양상모,장승엽,김태헌,김훈호,이호녕,윤종걸 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.31

We investigated the scaling behavior of ferroelectric (FE) hysteresis loops as a function of the applied field amplitude (E_0) in a high-quality epitaxial PbZr_(0.2)Ti_(0.8O3) (PZT) thin film. We observed that the areas of the polarization-electric field hysteresis loops (A) followed the scaling law A ∝ E^α_0, with the exponent α = 0.45 ± 0.01. This result is in excellent agreement with the theoretical prediction of α by the two-dimensional Ising model. In addition, we found that the coercive field (E_C) showed E_C/E^γ_0 with the exponent γ = 0.28 ± 0.01. We attribute this relationship to the difference in the sweep rate of the field amplitude E_0. From the obtained γ value, the growth dimension of FE domains is found to be about 1.68 in our epitaxial PZT thin film.

Superdomain structure and high conductivity at the vertices in the (111)- oriented epitaxial tetragonal Pb(Zr,Ti)O3 thin film

양상모,신영재,Yoshitaka Ehara,Hiroshi Funakubo,윤종걸,James F. Scott,노태원 한국물리학회 2019 Current Applied Physics Vol.19 No.4

Recently, in ferroelectric materials, there have been many experimental efforts to find out more intriguing topological objects and their functionalities, such as conduction property. Here we investigated ferroelectric domain structures and related topological defects in the (111)-oriented epitaxial tetragonal PbZr0.35Ti0.65O3 thin film. Systematic piezoresponse force microscopy measurements revealed that the field-induced polarization switching can form thermodynamically stable superdomain structures composed of nano-sized stripe subdomains. Within such superdomain structures, we observed the exotic equilateral triangular in-plane flux-closure domains composed of three stripe domain bundles with 120/120/120 degrees of separation. The conductive- atomic force microscopy measurements under vacuum showed that some vertices have significantly higher conductivity compared to other surrounding regions. This work highlights electric field-driven polarization switching and unique crystallographic symmetry (here, three-fold rotational symmetry) can generate exotic ferroelectric domain structures and functional topological defects, such as conductive vertices.

Fabrication and Thickness Dependent Properties of Ferroelectric Heterostructure

김용수,노태원,D.H. Kim,J.D. Kim,윤종걸,J.H. Kong,부상돈,박윤 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1

A high quality epitaxial SrRuO3(SRO)/BaTiO3(BTO)/SRO/SrTiO3 (001) heterostructure was grown by pulsed laser deposition with in situ re ection high-energy electron diraction. The growth mode and crystallinity of the heterostructure were veried by X-ray diraction and atomic force microscopy. Ferroelectric (FE) hysteresis loops could be observed down to 9 nm of BTO thickness. Remanent polarization decreased as the FE layer thickness decreased. In addition, all the capacitors showed imprint phenomena. The strength of the imprint increased as the BTO layer thickness decreased. Possible origins of the thickness-dependent imprint and the polarization reduction are discussed.