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임성일,Im, Seongil 한국진공학회 2018 진공 이야기 Vol.5 No.2
wo dimensional (2D) van der Waals (vdW) nanosheet semiconductors have recently attracted much attention from researchers because of their potentials as active device materials toward future nano-electronics and -optoelectronics. This review mainly focuses on the features and applications of state-of-the-art vdW 2D material devices which use transition metal dichalcogenides, graphene, hexagonal boron nitride (h-BN), and black phosphorous: field effect transistors (FETs), complementary metal oxide semiconductor (CMOS) inverters, Schottky diode, and PN diode. In a closing remark, important remaining issues of 2D vdW devices are also introduced as requests for future electronics and photonics applications.
Facile phase transition to β- from α-SnSe by uniaxial strain
Cha Sun-Kyung,Im Seongil,Ryu Byungki,Kim Yong-Sung 한국물리학회 2023 Current Applied Physics Vol.45 No.-
We investigate the phase transition between uniaxially strained α- and β-SnSe using density functional theory calculations and suggest that uniaxial strain can enable a facile phase transition to the β phase. Increasing the interlayer spacing along the a-axis and, more effectively, applying compressive strain in the corrugated direction along the c-axis in α-SnSe are found to decrease the β-phase energy with respect to α. Where the phase transition temperature Tc of unconstrained SnSe is 800 K, the Tc of a-axis +2.6% tensile strained α-SnSe is estimated to be 600 K, while the Tc of c-axis −3.8% compressive strained α-SnSe is estimated to be 400 K. The uniaxial strain engineering can lower the optimal operation temperature of SnSe-based thermoelectric applications.
Performance enhancement of multilayer MoS2 phototransistors via photoresist encapsulation
Sunwoo Hyeyeon,Jeong Yeonsu,Im Seongil,Choi Woong 한국물리학회 2022 Current Applied Physics Vol.41 No.-
We propose the encapsulation of bottom-gate multilayer MoS2 phototransistors with an AZ®5214E photoresist as an effective device design to enhance the optoelectronic properties of the phototransistors. The photoresist-encapsulated MoS2 phototransistors, based on mechanically exfoliated MoS2 crystals, exhibited an improved device performance. After the photoresist encapsulation, the responsivity and detectivity of the device increased by seven-fold to 3.2 × 103 A W-1 and by five-fold to 2.3 × 1012 Jones, respectively, under a 650-nm laser with an incident power density of 2.1 mW cm-2. We attribute the observed enhancement in the phototransistor performance to the enhanced electrical properties owing to the n-type doping via photoresist encapsulation. These results demonstrate that MoS2 phototransistors can achieve high performance without complicated device architecture and process, and thus, photoresist encapsulation presents an effective method for developing high-performance two-dimensional optoelectronic devices.
Lee, Byoung H,Lee, Kwang H,Im, Seongil,Sung, Myung M American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.12
<P>We report a vapor-phase molecular layer deposition (MLD) of self-assembled multilayer thin films for organic thin-film transistor. In the present MLD process, alkylsiloxane self-assembled multilayers (SAMs) were grown under vacuum by repeated sequential adsorptions of C=C-terminated alkylsilane and aluminum hydroxide with ozone activation. The MLD method is a self-controlled layer-by-layer growth process, and is perfectly compatible with the atomic layer deposition (ALD) method. The SAMs films prepared exhibited good mechanical flexibility and stability, excellent insulating properties, and relatively high dielectric capacitances of 374 nF/cm2 with a high dielectric strength of 4 MV/cm. They were then used as a 12 nm-thick dielectric for pentacene-based thin-film transistors (TFTs), which showed a maximum field effect mobility of 0.57 cm2/V s, operating at -4 V with an on/off current ratio of approximately 10(3).</P>
Park, Jae Chul,Lee, Ho-Nyeon,Im, Seongil American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.15
<P>Thin-film transistor (TFT) is a key component of active-matrix flat-panel displays (AMFPDs). These days, the low-temperature poly silicon (LTPS) TFTs are to match with advanced AMFPDs such as the active matrix organic light-emitting diode (AMOLED) display, because of their high mobility for fast pixel switching. However, the manufacturing process of LTPS TFT is quite complicated, costly, and scale-limited. Amorphous oxide semiconductor (AOS) TFT technology is another candidate, which is as simple as that of conventioanl amorphous (a)-Si TFTs in fabrication but provides much superior device performances to those of a-Si TFTs. Hence, various AOSs have been compared with LTPS for active channel layer of the advanced TFTs, but have always been found to be relatively inferior to LTPS. In the present work, we clear the persistent inferiority, innovating the device performaces of a-IZO TFT by adopting a self-aligned coplanar top-gate structure and modifying the surface of a-IZO material. Herein, we demonstrate a high-performance simple-processed a-IZO TFT with mobility of ∼157 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>, SS of ∼190 mV dec<SUP>–1</SUP>, and good bias/photostabilities, which overall surpass the performances of high-cost LTPS TFTs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-15/am401128p/production/images/medium/am-2013-01128p_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am401128p'>ACS Electronic Supporting Info</A></P>