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Properties of Silicon for Photoluminescence
Baek, Dohyun The Korean Vacuum Society 2014 Applied Science and Convergence Technology Vol.23 No.3
For more than five decades, silicon has dominated the semiconductor industry that supports memory devices, ICs, photovoltaic devices, etc. Photoluminescence (PL) is an attractive silicon characterization technique because it is contactless and provides information on bulk impurities, defects, surface states, optical properties, and doping concentration. It can provide high resolution spectra, generally with the sample at low temperature and room-temperature spectra. The photoluminescence properties of silicon at low temperature are reviewed and discussed in this study. In this paper, silicon bulk PL spectra are shown in multiple peak positions at low temperature. They correspond with various impurities such as In, Al, and Be, phonon interactions, for example, acoustical phonons and optical phonons, different exciton binding energies for boron and phosphorus, dislocation related PL emission peak lines, and oxygen related thermal donor PL emissions.
Properties of Silicon for Photoluminescence
Dohyun Baek 한국진공학회(ASCT) 2014 Applied Science and Convergence Technology Vol.23 No.3
For more than five decades, silicon has dominated the semiconductor industry that supports memory devices, ICs, photovoltaic devices, etc. Photoluminescence (PL) is an attractive silicon characterization technique because it is contactless and provides information on bulk impurities, defects, surface states, optical properties, and doping concentration. It can provide high resolution spectra, generally with the sample at low temperature and room-temperature spectra. The photoluminescence properties of silicon at low temperature are reviewed and discussed in this study. In this paper, silicon bulk PL spectra are shown in multiple peak positions at low temperature. They correspond with various impurities such as In, Al, and Be, phonon interactions, for example, acoustical phonons and optical phonons, different exciton binding energies for boron and phosphorus, dislocation related PL emission peak lines, and oxygen related thermal donor PL emissions.
Baek, Seung Bin,Moon, Dohyun,Graf, Robert,Cho, Woo Jong,Park, Sung Woo,Yoon, Tae-Ung,Cho, Seung Joo,Hwang, In-Chul,Bae, Youn-Sang,Spiess, Hans W.,Lee, Hee Cheon,Kim, Kwang S. National Academy of Sciences 2015 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.112 No.46
<P><B>Significance</B></P><P>Crystallographic observation of adsorbed gas molecules at high temperatures is a highly challenging task due to their rapid motion. We provide evidence of restrained motions in a self-assembled organic crystal with small isolated cages, inside which the confined CO<SUB>2</SUB> molecules can be identified with in situ X-ray diffraction technique at the high temperature. Although the crystal is nonporous, the CO<SUB>2</SUB> molecules can permeate into the crystal because of thermally activated transient pathways between the cages. We show that the flexible nature of the transient pathways leads to the temperature-driven reversible CO<SUB>2</SUB> sorption, understanding of which can contribute to the design of a system with controlled capture/release of gas molecules.</P><P>Crystallographic observation of adsorbed gas molecules is a highly difficult task due to their rapid motion. Here, we report the in situ single-crystal and synchrotron powder X-ray observations of reversible CO<SUB>2</SUB> sorption processes in an apparently nonporous organic crystal under varying pressures at high temperatures. The host material is formed by hydrogen bond network between 1,3,5-tris-(4-carboxyphenyl)benzene (H<SUB>3</SUB>BTB) and <I>N,N</I>-dimethylformamide (DMF) and by π–π stacking between the H<SUB>3</SUB>BTB moieties. The material can be viewed as a well-ordered array of cages, which are tight packed with each other so that the cages are inaccessible from outside. Thus, the host is practically nonporous. Despite the absence of permanent pathways connecting the empty cages, they are permeable to CO<SUB>2</SUB> at high temperatures due to thermally activated molecular gating, and the weakly confined CO<SUB>2</SUB> molecules in the cages allow direct detection by in situ single-crystal X-ray diffraction at 323 K. Variable-temperature in situ synchrotron powder X-ray diffraction studies also show that the CO<SUB>2</SUB> sorption is reversible and driven by temperature increase. Solid-state magic angle spinning NMR defines the interactions of CO<SUB>2</SUB> with the organic framework and dynamic motion of CO<SUB>2</SUB> in cages. The reversible sorption is attributed to the dynamic motion of the DMF molecules combined with the axial motions/angular fluctuations of CO<SUB>2</SUB> (a series of transient opening/closing of compartments enabling CO<SUB>2</SUB> molecule passage), as revealed from NMR and simulations. This temperature-driven transient molecular gating can store gaseous molecules in ordered arrays toward unique collective properties and release them for ready use.</P>
Choi, Pyungho,Baek, Dohyun,Heo, Sung,Choi, Byoungdeog Elsevier 2018 THIN SOLID FILMS - Vol.652 No.-
<P><B>Abstract</B></P> <P>Hafnium‑zirconium silicate (HfZr-silicate, (HfZrO<SUB>4</SUB>)<SUB>1−x</SUB>(SiO<SUB>2</SUB>)<SUB>x</SUB>) thin films were developed for advanced gate stack applications by incorporating Si atoms into virgin hafnium‑zirconium oxide (HfZrO<SUB>4</SUB>) via atomic-layer deposition, yielding films with varying Si content (x=0.10, 0.15, and 0.20). Electron conduction behavior was responsible for a reduction in the gate leakage current of HfZr-silicate compared to pure HfZrO<SUB>4</SUB> films and was clearly explained by a conduction-electron generation model. Furthermore, HfZr-silicate-based structures exhibited less charge trapping and featured improved interfacial stability when in contact with Si substrate compared to virgin HfZrO<SUB>4</SUB>, although they both experienced bias and thermal stress. These phenomena were associated with the formation of an interfacial layer (IL) between virgin HfZrO<SUB>4</SUB> and the Si substrate, while there was no IL for the HfZr-silicate. With regard to the electrical properties of the films with varying Si incorporation, film with 15% SiO<SUB>2</SUB> was recommended as a high dielectric constant candidate due to its superior electrical properties and outstanding durability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> (HfZrO<SUB>4</SUB>)<SUB>1−x</SUB>(SiO<SUB>2</SUB>)<SUB>x</SUB> dielectric films were developed and characterized. </LI> <LI> Thermal stabilities were enhanced with incorporation of SiO<SUB>2</SUB>. </LI> <LI> A film with 15% SiO<SUB>2</SUB> was demonstrated to be a high dielectric constant candidate. </LI> </UL> </P>
A Study on the Electrical Characteristic Analysis of c-Si Solar Cell Diodes
Pyungho Choi,Hyojung Kim,Dohyun Baek,Byoungdeog Choi 대한전자공학회 2012 Journal of semiconductor technology and science Vol.12 No.1
A study on the electrical characteristic analysis of solar cell diodes under experimental conditions of varying temperature and frequency has been conducted. From the current-voltage (I-V) measurements, at the room temperature, we obtained the ideality factor (n) for Space Charge Region (SCR) and Quasi-Neutral Region (QNR) of 3.02 and 1.76, respectively. Characteristics showed that the value of n (at SCR) decreases with rising temperature and n (at QNR) increases with the same conditions. These are due to not only the sharply increased SCR current flow but the activated carrier recombination in the bulk region caused by defects such as contamination, dangling bonds. In addition, from the I-V measurements implemented to confirm the junction uniformity of cells, the average current dispersion was 40.87% and 10.59% at the region of SCR and QNR, respectively. These phenomena were caused by the pyramidal textured junction structure formed to improve the light absorption on the device’s front surface, and these affect to the total diode current flow. These defect and textured junction structure will be causes that solar cell diodes have non-ideal electrical characteristics compared with general p-n junction diodes. Also, through the capacitance-voltage (C-V) measurements under the frequency of 180 ㎑, we confirmed that the value of built-in potential is 0.63 V.
Role of the buffer solution in the chemical deposition of CdS films for CIGS solar cell applications
Lee, Sooho,Kim, Donguk,Baek, Dohyun,Hong, Byoungyou,Yi, Junsin,Lee, Jaehyeong,Park, Yong Seob,Choi, Wonseok Korean Physical Society 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.10
In this work, the effects of NH4Ac on the structural and the electro-optical properties of CdS films were investigated. CdS thin films were deposited on soda-lime glass and indium-tin-oxide (ITO) coated glass from a chemical bath containing 0.025 M cadmium acetate, 0 M similar to 0.2 M ammonium acetate, 0.5 M thiourea, and ammonia. Cadmium acetate was the cadmium source, ammonium acetate served as a buffer, ammonia was the complexing agent, and thiourea was the source of sulfur. A commonl- available chemical bath deposition system was successfully modified to obtain precise control over the pH of the solution at 75 A degrees C during the deposition. Chemically deposited CdS films were studied by using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), optical transmittance, and electrical resistivity measurements.
Nam-Hyun Lee,Dohyun Baek,Bongkoo Kang IEEE 2011 IEEE electron device letters Vol.32 No.7
<P>This paper investigates the degradation mechanism of a nanoscale n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) that is subjected to off-state stress at high temperature and the impact of stress-induced defects on threshold voltage <I>V</I><SUB>th</SUB> during drain relaxation. Experimental results indicate that acceptor-like interface traps <I>N</I><SUB>it</SUB>, positive oxide charges <I>Q</I><SUB>ox</SUB>, and neutral electron traps were generated by the off-state stress. Although the <I>N</I><SUB>it</SUB> generated by the off-state stress caused an increase in <I>V</I><SUB>th</SUB>, it did not influence <I>V</I><SUB>th</SUB> during drain relaxation at a positive gate voltage. Drain relaxation filled the neutral electron traps and neutralized positive <I>Q</I><SUB>ox</SUB>'s, which increased <I>V</I><SUB>th</SUB> and decreased the off-current significantly. This new observation suggests that the off -state stress-induced defects in a nanoscaled nMOSFET should be seriously taken in evaluating the reliability of inverter circuits.</P>