• 제목/요약/키워드: bandgap engineering

검색결과 334건 처리시간 0.018초

기계화학적 방법으로 합성한 Cu2Zn(Sn,Ge)S4 나노결정과 이를 이용하여 제조한 태양전지 (Mechanochemically Synthesized Cu2Zn(Sn,Ge)S4 Nanocrystals and Their Application to Solar Cells)

  • 박보인;이승용;이도권
    • Current Photovoltaic Research
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    • 제4권3호
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    • pp.114-118
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    • 2016
  • $Cu_{1.8}Zn_{1.2}(Sn_{1-x}Ge_x)S_4$ (CZTGeS) nanocrystals were mechanochemically synthesized from elemental precursor powders without using any organic solvents and any additives. The composition of CZTGeS nanocrystals were systematically varied with different Ge mole fraction (x) from 0.1 to 0.9. The XRD, Raman spectroscopy, high-resolution TEM, and diffuse reflectance studies show that the as-synthesized CZTGeS nanocrystals exhibited consistent changes in various structural and optical properties as a function of x, such as lattice parameters, wave numbers for $A_1$ Raman vibration mode, interplanar distances (d-spacing), and optical bandgap energies. The bandgap energy of the synthesized CZTGeS nanocrystals gradually increases from 1.40 to 1.61 eV with increasing x from 0.1 to 0.9, demonstrating that Ge-doping is useful means to tune the bandgap of mechanochemically synthesized nanocrystals-based kesterite thin-film solar cells. The preliminary solar cell performance is presented with an efficiency of 3.66%.

2차원 층상 구조 전이금속 칼코겐화합물의 레이저 식각에 의한 직접-간접 띠간격 구조 연구 (A Study on Indirect-Direct Bandgap Structures of 2D-layered Transition Metal Dichalcogenides by Laser Etching)

  • 문은아;고필주
    • 한국전기전자재료학회논문지
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    • 제29권9호
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    • pp.576-580
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    • 2016
  • Single-layered transition metal dichalcogenides (TMDs) exhibit more interesting physical properties than those of bulk TMDs owing to the indirect to direct bandgap transition occurring due to quantum confinement. In this research, we demonstrate that layer-by-layer laser etching of molybdenum diselenide ($MoSe_2$) flakes could be controlled by varying the parameters employed in laser irradiation (time, intensity, interval, etc.). We observed a dramatic increase in the photoluminescence (PL) intensity (1.54 eV peak) after etching the samples, indicating that the removal of several layers of $MoSe_2$ led to a change from indirect to direct bandgap. The laser-etched $MoSe_2$ exhibited the single $MoSe_2$ Raman vibration modes at ${\sim}239.4cm^{-1}$ and ${\sim}295cm^{-1}$, associated to out-of-plane $A_{1g}$ and in-plane ${E^1}_{2g}$ Raman modes, respectively. These results indicate that controlling the number of $MoSe_2$ layers by laser etching method could be employed for optimizing the performance of nano-electronic devices.

증착시 및 플라즈마 후처리에 의한 수소 주입이 투명 박막 트랜지스터에서 산화아연 채널층의 물성에 미치는 영향 (Effects of Hydrogen Injection by In-Situ and Plasma Post-Treatment on Properties of a ZnO Channel Layer in Transparent Thin Film Transistors)

  • 방정환;김원;엄현석;박진석
    • 반도체디스플레이기술학회지
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    • 제9권1호
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    • pp.35-40
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    • 2010
  • We have investigated the effects of hydrogen injection via in-situ gas addition ($O_2$, $H_2$, or $O_2$ + $H_2$ gas) and plasma post-treatment (Ar or Ar + H plasma) on material properties of ZnO that is considered to be as a channel layer in transparent thin film transistors. The variations in the electrical resistivity, optical transmittance and bandgap energy, and crystal quality of ZnO thin films were characterized in terms of the methods and conditions used in hydrogen injection. The resistivity was significantly decreased by injection of hydrogen; approximately $10^6\;{\Omega}cm$ for as-grown, $1.2\;{\times}\;10^2\;{\Omega}cm$ for in-situ with $O_2/H_2\;=\;2/3$ addition, and $0.1\;{\Omega}cm$ after Ar + H plasma treatment of 90 min. The average transmittance of ZnO films measured at a wavelength of 400-700 nm was gradually increased by increasing the post-treatment time in Ar + H plasma. The optical bandgap energy of ZnO films was almost monotonically increased by decreasing the $O_2/H_2$ ratio in in-situ gas addition or by increasing the post-treatment time in Ar + H plasma, while the post-treatment using Ar plasma hardly affected the bandgap energy. The role of hydrogen in ZnO was discussed by considering the creation and annihilation of oxygen vacancies as well as the formation of shallow donors by hydrogen.

Temperature Stable Current Source Using Simple Self-Bias Circuit

  • Choi, Jin-Ho
    • Journal of information and communication convergence engineering
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    • 제7권2호
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    • pp.215-218
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    • 2009
  • In this paper, temperature stable current and voltage references using simple CMOS bias circuit are proposed. To obtain temperature stable characteristics of bias circuit a bandgap reference concept is used in a conventional circuit. The parasitic bipolar transistors or MOS transistors having different threshold voltage are required in a bandgap reference. Thereby the chip area increase or the extra CMOS process is required compared to a standard CMOS process. The proposed reference circuit can be integrated on a single chip by a standard CMOS process without the extra CMOS process. From the simulation results, the reference current variation is less than ${\pm}$0.44% over a temperature range from - $20^{\circ}C$ to $80^{\circ}C$. And the voltage variation is from - 0.02% to 0.1%.

Bandwidth Enhancement for SSN Suppression Using a Spiral-Shaped Power Island and a Modified EBG Structure for a ${\lambda}$/4 Open Stub

  • Kim, Bo-Bae;Kim, Dong-Wook
    • ETRI Journal
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    • 제31권2호
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    • pp.201-208
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    • 2009
  • This paper proposes a spiral-shaped power island structure that can effectively suppress simultaneous switching noise (SSN) when the power plane drives high-speed integrated circuits in a small area. In addition, a new technique is presented which greatly improves the resonance peaks in a stopband by utilizing ${\lambda}$/4 open stubs on a conventional periodic electromagnetic bandgap (EBG) power plane. Both proposed structures are simulated numerically and experimentally verified using commercially available 3D electromagnetic field simulation software. The results demonstrate that they achieve better SSN suppression performance than conventional periodic EBG structures.

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밴드갭이 제어된 TiO2 를 이용한 자외선 차단제의 블루라이트 차단 및 SPF 부스팅 효과 (The Effect of Blue Light Interception and SPF Boosting of Sunscreen Prepared with Bandgap-controlled TiO2)

  • 왕성은;윤정경;정귀수;계성봉;노호식;정대수
    • 대한화장품학회지
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    • 제49권2호
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    • pp.159-167
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    • 2023
  • 이산화티타늄(TiO2)은 일반적으로 선크림 제제에 사용되어 빛의 물리적 산란 작용에 의해 피부 표면을 보호하고 유해한 자외선(UV)의 침투를 방지한다. 그러나 불활성 미네랄 성분으로 인해 피부에 사용시 백탁현상을 유발할 수 있다는 단점이 있다. 또한 백탁현상을 없애기 위해 TiO2 입자를 나노화 하면 가시광선 투과율을 증가시켜 백탁 현상을 감소시키지만 알레르기 염증과 같은 심각한 피부 트러블을 유발할 수 있다. 이러한 문제를 극복하기 위해 본 연구에서는 산소 결핍 구조 및 질소량 제어를 이용하여 TiO2의 밴드갭을 제어하고, 결과적으로 피부 맞춤형 유색 TiO2를 개발하였다. 이는 백탁 현상을 감소시킬 수 있을 뿐만 아니라 활성산소를 유발하여 피부 노화를 촉진시키는 것으로 알려진 블루라이트를 효과적으로 차단할 수 있다. 본 연구에서 제안된 밴드갭 제어 TiO2 화합물은 저자극이고 스펙트럼이 넓으며 환경친화적이다. 또한 이는 자외선 차단제의 sun protection factor (SPF)를 획기적으로 향상시켜 블루라이트 차단 제품에 적용할 수 있을 것으로 기대된다.

Cd 함량 변화에 따른 ZnO의 구조적, 광학적 특성 변화에 관한 연구 (Structural and optical properties of ZnO depending on Cd content)

  • 강홍성;김재원;임성훈;장현우;김건희;김종훈;이상렬
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 2005년도 춘계학술대회 논문집 디스플레이 광소자 분야
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    • pp.51-53
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    • 2005
  • $Zn_{1-x}Cd_xO$ thin films were grown on (0001) sapphire substrates by pulsed laser deposition. The energy bandgap of $Zn_{1-x}Cd_xO$ films decreases withincreasing Cd content. An increase of Cd content also leads to the emission broadening and degraded crystallinity. The absorption edge and ultraviolet emission peak shift to lower energy from 3.357 eV to 3.295 eV and 3.338 eV to 3.157 eV, respectively, with increasing Cd content from 0.3% to 3%. The Stokes' shift between the absorption and emission indicates the increase of localization of exciton with Cd content.

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Atomistic simulation of surface passivated wurtzite nanowires: electronic bandstructure and optical emission

  • Chimalgi, Vinay U.;Nishat, Md Rezaul Karim;Yalavarthi, Krishna K.;Ahmed, Shaikh S.
    • Advances in nano research
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    • 제2권3호
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    • pp.157-172
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    • 2014
  • The three-dimensional Nano-Electronic Modeling toolkit (NEMO 3-D) is an open source software package that allows the atomistic calculation of single-particle electronic states and optical response of various semiconductor structures including bulk materials, quantum dots, impurities, quantum wires, quantum wells and nanocrystals containing millions of atoms. This paper, first, describes a software module introduced in the NEMO 3-D toolkit for the calculation of electronic bandstructure and interband optical transitions in nanowires having wurtzite crystal symmetry. The energetics (Hamiltonian) of the quantum system under study is described via the tight-binding (TB) formalism (including $sp^3$, $sp^3s^*$ and $sp^3d^5s^*$ models as appropriate). Emphasis has been given in the treatment of surface atoms that, if left unpassivated, can lead to the creation of energy states within the bandgap of the sample. Furthermore, the developed software has been validated via the calculation of: a) modulation of the energy bandgap and the effective masses in [0001] oriented wurtzite nanowires as compared to the experimentally reported values in bulk structures, and b) the localization of wavefunctions and the optical anisotropy in GaN/AlN disk-in-wire nanowires.

GaN Power SIT의 설계변수에 따른 전기적 특성변화에 관한 연구 (A Study on the Electrical Characteristics with Design Parameters in GaN Power Static Induction Transistor)

  • 오주현;양성민;정은식;성만영
    • 한국전기전자재료학회논문지
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    • 제23권9호
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    • pp.671-675
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    • 2010
  • Gallium nitride (GaN), wide bandgap semiconductor, has attracted much attention because they are projected to have much better performance than silicon. In this paper, effects of design parameters change of GaN power static induction transistor (SIT) on the electrical characteristics (breakdown voltage, on resistance) were analyzed by computer simulation. According to the analyzed results, the optimization was performed to get power GaN SIT that has 600 V class breakdown voltage. As a result, we could get optimized 600 V class power GaN SIT that has higher breakdown voltage and lower On resistance with a thin (a several micro-meters) thickness of the channel layer.