• Title, Summary, Keyword: Energy Band Diagram

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C-V 측정을 통한 다이오드 소자의 온도 특성 분석

  • Choe, Pyeong-Ho;Kim, Sang-Seop;Choe, Byeong-Deok
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.284-284
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    • 2012
  • 본 연구에서는 다이오드 소자의 온도 증가에 따른 C-V 특성을 분석하였다. 180 kHz 주파수 조건에서 온도는 300 K에서 450 K까지 50 K 간격으로 가변하였다. 측정 결과 reverse bias 영역에서는 커패시턴스의 온도 의존성이 없었으나, forward bias 영역에서는 온도가 증가함에 따라 동일 전압에서의 커패시턴스가 증가하였다. 이로부터 온도가 증가 할수록 소자가 반전(inversion) 상태에서 축적(accumulation) 상태로 빨리 전환함을 확인하였으며, 1/C2-V 그래프로부터 온도 증가에 따른 전위장벽(Built-in potential, Vbi) 감소를 확인하였다. 전위장벽은 0.63 V에서 0.31 V로 온도 상승에 따라 약 0.1 V씩 감소하였다. 이는 energy band diagram에서 p-type 영역과 n-type 영역의 energy band 차가 감소해 공핍층 영역의 폭이 좁아짐을 의미한다. 공핍층의 두께 감소로 다이오드 전류의 급격한 증가뿐 아니라 위에서 언급한 바와 같은 C-V 특성을 보였다. 이번 연구에서는 기존의 보편화 된 I-V 측정을 통한 다이오드 소자 분석과는 달리 온도 변화에 따른 C-V 분석을 통해 소자 내부의 전위 장벽 및 공핍층 폭 감소에 따른 소자 특성 변화를 분석하였다.

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Tailoring the Electronic Structure of Anatase TiO2(001) Surface Through W and N Codoping: a DFT Calculation

  • Li, Zongbao;Wang, Xia;Xing, Xiaobo;Wang, Ying
    • Journal of the Korean Physical Society
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    • v.70 no.3
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    • pp.286-291
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    • 2017
  • Using density functional theory, we calculated the geometries, band structures and densities of states of W-doped, N-doped, and W/N-codoped anatase $TiO_2$ (001) and (101) surfaces, as well as while the formation energies, based on the overall reaction energy diagram. The calculated results reveal that, on the two surfaces, the absorption of W atoms are more stable than that of N atoms while a larger energy barrier blocks the transfer of W atoms from the surfaces to the body. For $TiO_2(001)$, the W-doping and the N/W-codoping lead to a visible lattice distortion while the recombination of photo-generated electron-holes pairs is reduced. A comprehensive analysis of the electronic structures show that the band-gap narrows and a new W-N bond appears, which obviously enhance the photocatalytic activity.

A Study on the Various Organic Electroluminescent Devices Using Lanthanide Chelate Metal Complexes (란탄계 금속 착화합물을 이용한 다양한 유기 전기 발광 소자의 연구)

  • 표상우;이한성;김정수;이승희;김영관
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.529-532
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    • 1999
  • 본 연구에서는 유기 전기 발광 소자에서 녹색 발광층으로 사용되는 terbium(Tb) complexes와 europium(Eu) complex, 정공 수송층으로 사용되는 TPD (N, N\`-diphenyl-N,\`(3-methylphenyl)-1, 1\`biphenyl-4, 4\`-diamine), 그리고 전자 수송층으로 사용되는 Alq$_{3}$ (trois(8-hydroxyquinolino)aluminum), Bebq$_2$들의 Uv/Vis. 홉광도와 PL 스펙 트럼과 같은 광학적 특성을 조사하였으며 또한 이러한 물질들을 이용하여 다양한 종류의 유기 전기 발광 소자를 제작하고 제작된 소자들의 전류밀도-전압-조도 등의 전기 . 광학적 특성을 조사하였으며, 그 결과 다 음과 같은 결곤을 얻을 수 있었다. 다양한 ligand를 갖는 Tb complex들의 경우에도 EL 스펙트럼의 파장대 (wavelength)는 546nm~548nm의 녹색 발광을 하는 것을 알 수 있었고, 제작된 소자 중에서 Tb(ACAC)$_3$(Phen) 을 발광충으로 하고, TPD, 그리고 Bebq$_2$를 각각 정공 수송층, 전자 수송 층으로 한 소자가 가장 낮은 구동 전압을 갖는다는 것을 확인하였으며 logJ-logV 특성에서도 모든 전계 구간에서 이러한 구조의 소자가 가장 높은 전류밀도를 나타냈으며 저 전계 구간에서 전류밀도 타이가 가장 컸다. 소자의 전류밀도와 휘도의 관계에 있어서는 제작된 네 종류의 소자 중 Tb(ACAC)3(Cl-Phen)를 발광층으로 하고 TPD, 그리고 Bebq2를 각각 정공 수송층, 전자 수송 층으로 한 소자가 가장 휘도가 우수한 것을 알 수 있었다. 또한 red (europium complex), green (terbium complex), 그리고 blue (TPD) 색깔을 나타내는 유기 재료를 사용하여 한 소자에서 백색 소자를 제작하여 cyclic voltametric방법을 이용하여 각 유기 물질들의 에너지 준위를 조사하여, 각각의 소자들을 에너지 밴드 다이어그램(energy band diagram)으로 자세히 설명하였다.

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A Study on the Photoconductive Cell Production of New Semiconductor Using MgGa$_2$Se$_4$Single Crystals (MgGa$_2$Se$_4$신반도체 단결정을 사용한 광전도도 소자 제작에 관한 연구)

  • 김형곤;김형윤;이광석;이기형
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.17 no.1
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    • pp.58-67
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    • 1992
  • Optical absorption and photoluminescences(PL) of MgGa2Se4 and MgGa2Se4 : Co2+ single crustals were guown by the Bridgman method have been investigated in the visible and near-in frared regions. The optical absorption spectrum showed three absorption peak at 760 nm(13158nm, -1, 1.63eV), 1640nm(6097cm-1, 0.75eV).and 2500nm(4000cm-1,0.49eV) which are assigned the electronic transitions between the ground state and excited states of Co2+ ions with Td sym-metry in MgGa2Se4 host lattice. In PL spectrum the visible emission bands as well as the infrared emission band in these single cuystals are obserned. The visible emission bands are explained due to the radiative transitions of electrons from quasi continusly distributed tarps below the bottom of the conduction band to acceptor levels above the top of the valence band in the proposed energy level scheme. At the same time, it is considered that the infrated emission bands are attributed to electron transitions from the deep levels to the acceptor levels. The mechanism of the optical transition os well explained in terms of the energy diagram of MgGa2Se4.

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Surface Modification of Zinc Oxide Nanorods with Zn-Porphyrin via Metal-Ligand Coordination for Photovoltaic Applications

  • Koo, Jae-Hong;Cho, Jin-Ju;Yang, Jin-Ho;Yoo, Pil-J.;Oh, Kyung-Wha;Park, Ju-Hyun
    • Bulletin of the Korean Chemical Society
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    • v.33 no.2
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    • pp.636-640
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    • 2012
  • We modify ZnO nanorods with Zn-porphyrin to obtain the improved characteristics of energy transfer, which is further investigated for the applicability to photovoltaic devices. A nitrogen heterocyclic ligand containing a thiol group is covalently grafted onto the surface of finely structured ZnO nanorods with a length of 50-250 nm and a diameter of 15-20 nm. Zn-porphyrin is then attached to the ligand molecules by the mechanism of metalligand axial coordination. The resulting energy band diagram suggests that the porphyrin-modified ZnO nanorods might provide an efficient pathway for energy transfer upon being applied to photovoltaic devices.

Change in Opto-electrical Characteristics in Poly[3-octylthiophene-co-3-(4-fluorophenyl)thiophene] according to the Copolymerization Ratio (Poly[3-octylthiophene-co-3-(4-fluorophenyl)thiophene]에서 공중합 비율에 따른 전기 광학적 특성의 변화)

  • 신선호;정애영;김주현;이후성;김동표
    • Polymer(Korea)
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    • v.25 no.3
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    • pp.399-405
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    • 2001
  • Poly[3-octylthiophene-co-3-(4-fluorophenyl)thiophene]s were synthesized in 2:1, 1:1, and 1:2 mole ratios, and organic electroluminescent devices were fabricated using the copolymers. The opto-electrical properties of the copolymers were studied by PL, EL spectra, I-V, and V-L curves of the organic electroluminescent devices in conjunction with the energy band diagrams which were obtained from the cyclic voltammogram and the electronic absorption spectra. The LUMO energy level of P(OT/FPT)(1:1) is the lowest as -3.35 eV. In the copolymers P(OT/FPT)(2:1) and P(OT/FPT)(1:1) the ${\lambada}_{max}$ in the PL and EL spectra red-shifted as the mole ratio of fluorophenyl group increased while in P(OT/FPT)(1:2) it showed a blue-shift. This indicates that the backbone chain is twisted due to the steric hinderance of the fluorophenyl group leading to shorter ${\pi}$-conjugation length. P(OT/FPT)(1:1) showed the highest EL intensity and the highest power efficiency among the three copolymers. In P(OT/FPT)(1:2) the roughness of the film surface causes unusually high local leakage current leading to the low efficiency of electroluminescence.

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Effect of Transition Metal Dopant on Electronic State and Chemical Bonding of MnO2 (MnO2의 전자상태 및 화학결합에 미치는 천이금속 첨가의 효과)

  • 이동윤;김봉서;송재성;김양수
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.17 no.7
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    • pp.691-696
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    • 2004
  • The electronic state and chemical bonding of $\beta$-MnO$_2$ with transition metal dopants were theoretically investigated by DV-X$_{\alpha}$ (the discrete variational X$_{\alpha}$) method, which is a sort of the first principles molecular orbital method using the Hartree-Fock-Slater approximation. The calculations were performed with a $_Mn_{14}$ MO$_{56}$ )$^{-52}$ (M = transition metals) cluster model. The electron energy level, the density of states (DOS), the overlap population, the charge density distribution, and the net charges, were calculated. The energy level diagram of MnO$_2$ shows the different band structure and electron occupancy between the up spin states and down spin states. The dopant levels decrease between the conduction band and the valence band with the increase of the atomic number of dopants. The covalency of chemical bonding was shown to increase and ionicity decreased in increasing the atomic number of dopants. Calculated results were discussed on the basis of the interaction between transition metal 3d and oxygen 2p orbital. In conclusion it is expected that when the transition metals are added to MnO$_2$ the band gap decreases and the electronic conductivity increases with the increase of the atomic number of dopants. the atomic number of dopants.

Work function variation of doped ZnO nanorods by Kelvin probe force microscopy

  • Ben, Chu Van;Hong, Min-Chi;Yang, Woo-Chul
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.446-446
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    • 2011
  • One dimensional (1-D) structures of ZnO nanorods are promising elements for future optoelectronic devices. However there are still many obstacles in fabricating high-quality p-type ZnO up to now. In addition, it is limited to measure the degree of the doping concentration and carrier transport of the doped 1-D ZnO with conventional methods such as Hall measurement. Here we demonstrate the measurement of the electronic properties of p- and n-doped ZnO nanorods by the Kelvin probe force microscopy (KPFM). Vertically aligned ZnO nanorods with intrinsic n-doped, As-doped p-type, and p-n junction were grown by vapor phase epitaxy (VPE). Individual nanowires were then transferred onto Au films deposited on Si substrates. The morphology and surface potentials were measured simultaneously by the KPFM. The work function of the individual nanorods was estimated by comparing with that of gold film as a reference, and the doping concentration of each ZnO nanorods was deduced. Our KPFM results show that the average work function difference between the p-type and n-type regions of p-n junction ZnO nanorod is about ~85meV. This value is in good agreement with the difference in the work function between As-doped p- and n-type ZnO nanorods (96meV) measured with the same conditions. This value is smaller than the expected values estimated from the energy band diagram. However it is explained in terms of surface state and surface band bending.

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Electric-field induced si-graphene heterostructure solar cell using top gate

  • Won, Ui-Yeon;Yu, U-Jong
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.287.2-287.2
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    • 2016
  • Silicon has considerably good characteristics on electron, hole mobility and its price. With 2-D sinlge-layer Graphene/n-Si heterojunction solar cell shows that in one sun condition exhibit power conversion efficiency(PCE) of 10.1%. This photovoltaic effect was achieved by applying gate voltage to the Schottky junction of the heterostructure solar cell. Energy band diagram shows that Schottky barrier between Si and graphene can be adjust by the external electric field. because of the fermi level of the graphene can be changed by external gate voltage, we can control the Schottkky barrier of the heterostructure solar cell. The ratio between generated power of solar cell and consumption electrical power is remarkable. Since we use the graphene as the top gate electrode, most of the sun light can penetrate into the active area.

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Dependence of Electrons Loss Behavior on the Nitride Thickness and Temperature for Charge Trap Flash Memory Applications

  • Tang, Zhenjie;Ma, Dongwei;Jing, Zhang;Jiang, Yunhong;Wang, Guixia;Li, Rong;Yin, Jiang
    • Transactions on Electrical and Electronic Materials
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    • v.15 no.5
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    • pp.245-248
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    • 2014
  • $Pt/Al_2O_3/Si_3N_4/SiO_2/Si$ charge trap flash memory structures with various thicknesses of the $Si_3N_4$ charge trapping layer were fabricated. According to the calculated and measured results, we depicted electron loss in a schematic diagram that illustrates how the trap to band tunneling and thermal excitation affects electrons loss behavior with the change of $Si_3N_4$ thickness, temperature and trap energy levels. As a result, we deduce that $Si_3N_4$ thicknesses of more than 6 or less than 4.3 nm give no contribution to improving memory performance.