• Title, Summary, Keyword: Amorphous GeSe

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Deformation of Amorphous GeSe2 Film under Uniaxial Pressure Applied at Elevated Temperatures

  • Jin, Byeong Kyou;Lee, Jun Ho;Yi, Jeong Han;Lee, Woo Hyung;Shin, Sang Yeol;Choi, Yong Gyu
    • Journal of the Korean Ceramic Society
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    • v.52 no.2
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    • pp.108-113
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    • 2015
  • In an effort to evaluate the practicability of an imprinting technique for amorphous chalcogenide film in Ge-based compositions, we investigate the deformation behavior of the surface of amorphous $GeSe_2$ film deposited via a thermal evaporation route according to varying static loads applied at elevated temperatures. We observe that, under these static loading conditions, crystallization tends to occur on its surface relatively more easily than in As-based $As_2Se_3$ films. As for the present $GeSe_2$ film, higher processing temperatures are required in order to make its surface reflect the given stamp patterns well; however, in this case, its surface becomes partially crystallized in the monoclinic $GeSe_2$ phase. The increased vulnerability of this amorphous $GeSe_2$ film toward surface crystallization under static loading, when compared with the $As_2Se_3$ counterpart, is explained in terms of the topological aspects of its amorphous structure.

Holographic grating data erasure of amorphous Ag/As-Ge-Se-S multi-layer thin film (비정질 Ag/As-Ge-Se-S 다층박막에 형성된 홀로그램 격자의 소거에 관한 연구)

  • Kim, Jin-Hong;Koo, Yong-Woon;Koo, Sang-Mo;Chung, Hong-Bay
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.112-113
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    • 2006
  • In this paper. we investigated a characteristic of holographic grating data erasure with non-polarized beam at amorphous chalcogenide As-Ge-Se-S thin film. A sample of holographic grating data was formed with DPSS laser for setup. Then, the erasure process was performed with He-Ne laser vertically at sample. As-Ge-Se-S(single layer). Ag/As-Ge-Se-S(double layer) and As-Ge-Se-S/Ag/As-Ge-Se-S(multi-layer) are manufactured to compare their characteristic of erasure.

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Switching Characteristics of Amorphous GeSe TFT for Switching Device Application

  • Nam, Gi-Hyeon;Kim, Jang-Han;Jo, Won-Ju;Jeong, Hong-Bae
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.403-404
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    • 2012
  • We fabricated TFT devices with the GeSe channel. A single device consists of a Pt source and drain, a Ti glue layer and a GeSe chalcogenide channel layer on SiO2/Si substrate which worked as the gate. We confirmed the drain current with variations of gate bias and channel size. The I-V curves of the switching device are shown in Fig. 1. The channel of the device always contains amorphous state, but can be programmed into two states with different threshold voltages (Vth). In each state, the device shows a normal Ovonic switching behavior. Below Vth (OFF state), the current is low, but once the biasing voltage is greater than Vth (ON state), the current increases dramatically and the ON-OFF ratio is high. Based on the experiments, we draw the conclusion that the gate voltage can enhance the drain current, and the electric field by the drain voltage affects the amorphous-amorphous transition. The switching device always contains the amorphous state and never exhibits the Ohmic behavior of the crystalline state.

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Resistive Switching Characteristics of Amorphous GeSe ReRAM without Metalic Filaments Conduction

  • Nam, Gi-Hyeon
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.368.1-368.1
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    • 2014
  • We proposed amorphous GeSe-based ReRAM device of metal-insulator-metal (M-I-M) structure. The operation characteristics of memory device occured unipolar switching characteristics. By introducing the concepts of valance-alternation-pairs (VAPs) and chalcogen vacancies, the unipolar resistive switching operation had been explained. In addition, the current transport behavior were analyzed with space charge effect of VAPs, Schottky emission in metal/GeSe interface and P-F emission by GeSe bulk trap in mind. The GeSe ReRAM device of M-I-M structure indicated the stable memory switching characteristics. Furthermore, excellent stability, endurance and retention characteristics were also verified.

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Phase change properties of amorphous $Ge_1Se_1Te_2$ and $Ge_2Se_2Te_5$ chalcogenide thin films. (비정질 $Ge_1Se_1Te_2$$Ge_2Se_2Te_5$ 칼코게나이드박막의 상변화특성)

  • Chung, Hong-Bay;Cho, Won-Ju;Koo, Sang-Mo
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.118-119
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    • 2006
  • In the present work, we investigate the basic physical and thermal properties and electrical resistance change due to phase change in chalcogenide-based $Ge_1Se_1Te_2$ and $Ge_2Se_2Te_5$ thin films. The phase transition from amorphous to crystalline states, and vice versa, of $Ge_1Se_1Te_2$ and $Ge_2Se_2Te_5$ thin films by applying electrical pulses have been studied. The reversible phase transition between the amorphous and crystalline states, which is accompanied by a considerable change in electrical resistivity, is exploited as means to store bits of information.

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A study on amorphous-amorphous phase transition of As-Se-S-Ge thin films (As-Se-S-Ge계 박막의 비정질-비정질 상변환 연구)

  • Lee, S.J.;Lee, Y.J.;Chang, H.B.;Kim, J.B.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.73-76
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    • 1992
  • The amorphous phase of bulk and thin film in the As-Se-S-Ge system was observed by X-ray diffraction. Thermal analysis using DSC, DTA and TGA method has been used for the determination of the glass transition temperature, Tg. The glass transition temperature, Tg for the composition were $238^{\circ}C$ in $As_{40}Se_{15}S_{35}Ge_{10}$ and $231^{\circ}C$ in $AS_{40}Se_{25}S_{25}Ge_{10}$ and $As_{40}Se_{50}Ge_{10}$. The phase seperation of continuous phase and dispersive phase was observed by the optical texture of the polarizing microscope. Also, the glass transition temperature of the thin film was near $200^{\circ}C$. As the results of SEM-EDS analysis, the phase transition of the films by thermal treatment and light illumination was the amorphous to amorphous.

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Preparation and Characterization of $Ge_{20}As_{20}Se_{60}$ Amorphous Chalcogenide Thin Film by Spin Coating (Spin-coating에 의한 $Ge_{20}As_{20}Se_{60}$ 비정질 chalcogenide 박막의 제조 및 광특성 분석)

  • 이강구;최세영
    • Journal of the Korean Ceramic Society
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    • v.37 no.3
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    • pp.219-226
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    • 2000
  • Amorphous Ge20As20Se60 chalcogenide thin films were prepared by spin coating technique from mixed solutions of As40Se60 and Ge40Se60 dissolved in ethylenediamine. Films were prepared at a roating speed of 3500 rpm and spinning time was 10 second and heat-treateed at 27$0^{\circ}C$ for 1 hour. The resulting film thickness and RMS roughness were approximately 340 nm and 15$\AA$. Photostructure changes were investigated with 514.5nm Ar+ laser irradiation and heat-treatment. After Ar+ laser irradiation, transmittance and transmission efficiency decreased respectively up to 24.9% at 2.43 eV and 67.5% at 3.27 eV, and absorption edge shifted toward long wavelength. Optical bandgap changed from 2.03 to 1.83 eV, and absoprtion coefficient and absorption efficiency increased up to 0.33$\times$105cm-1 at 3.37eV and 88.3% at 1.31 eV, respectively. These photodarkening state were recovered reversibly by heat-treatment at 27$0^{\circ}C$ for 1 hour. Photodarkening and thermal bleaching effects by laser irradiation and heat-treatment revealed reversible amorphous-to-amorphous transition varying only coordination number.

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Optical Gap Bowing and Phonon Modes of Amorphous Ge1-x-ySexAsy Thin Films

  • So, Hyeon-Seop;Park, Jun-U;Jeong, Dae-Ho;Lee, Ho-Seon;Sin, Hye-Yeong;Yun, Seok-Hyeon;An, Hyeong-U;Kim, Su-Dong;Lee, Su-Yeon;Jeong, Du-Seok;Jeong, Byeong-Gi
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.288.1-288.1
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    • 2014
  • We investigated the optical properties of Ge1-xSex and Ge1-x-ySexAsy amorphous semiconductor films using spectroscopic ellipsometry and Raman spectroscopy. The dielectric functions and absorption coefficients of the amorphous films were determined from the measured ellipsometric angles. We obtained the optical gap energies and Urbach energies from the absorption coefficients, and found a strong bowing effect in the optical gap energy of Ge1-x-ySexAsy where the endpoint binaries were Ge0.50Se0.50 and Ge0.31As0.69. Based on the correlation between optical gap energies and Urbach energies, the large bowing parameter was attributed to the electronic disorder. We found the composition dependence of several phonon modes using Raman spectroscopy. For Ge1-x-ySexAsy, the D mode (232-267 cm-1) changed from As-As (or As3 pyramid), to As(Se1/2)3 pyramid, and finally to Se clusters, as the Se composition increased. Resonant Raman phenomenon was observed in Ge0.38Se0.62 at a laser excitation of 514 nm (2.41 eV). We verified that this laser energy corresponds to the transition energy of Ge0.38Se0.62 using the second derivative of the dielectric function of Ge0.38Se0.62.

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Holographic Properties in Amorphous As-Ge-Se-S with Ag Thickness (Ag의 두께에 따른 비정질 As-Ge-Se-S의 홀로그래픽 특성연구)

  • Kim, Chung-Hyeok
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.25 no.3
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    • pp.213-217
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    • 2012
  • In this study, we have investigated the holographic grating formation on Ag-doped amorphous As-Ge-Se-S thin films. The dependence of diffraction efficiency as afunction of Ag layer thickness has been investigated in this amorphous chalcogenide films. Holographic gratings was formed using [P:P] polarized Diode Pumped Solid State laser (DPSS, 532.0 nm). The diffraction efficiency was obtained by +1st order intensity. The results were shown that the diffraction efficiency of Ag/AsGeSeS double layer thin films for the Ag thickness, the maximum grating diffraction efficiency using 60 nm Ag layer is 0.96%.

Operating Characteristics of Amorphous GeSe-based Resistive Random Access Memory at Metal-Insulator-Silicon Structure (금속-절연층-실리콘 구조에서의 비정질 GeSe 기반 Resistive Random Access Memory의 동작 특성)

  • Nam, Ki-Hyun;Kim, Jang-Han;Chung, Hong-Bay
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.29 no.7
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    • pp.400-403
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    • 2016
  • The resistive memory switching characteristics of resistive random access memory (ReRAM) using the amorphous GeSe thin film have been demonstrated at Al/Ti/GeSe/$n^+$ poly Si structure. This ReRAM indicated bipolar resistive memory switching characteristics. The generation and the recombination of chalcogen cations and anions were suitable to explain the bipolar switching operation. Space charge limited current (SCLC) model and Poole-Frenkel emission is applied to explain the formation of conductive filament in the amorphous GeSe thin film. The results showed characteristics of stable switching and excellent reliability. Through the annealing condition of $400^{\circ}C$, the possibility of low temperature process was established. Very low operation current level (set current: ~ ${\mu}A$, reset current: ~ nA) was showed the possibility of low power consumption. Particularly, $n^+$ poly Si based GeSe ReRAM could be applied directly to thin film transistor (TFT).