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Bang, Seokhwan,Lee, Seungjun,Park, Taeyoung,Ko, Youngbin,Shin, Seokyoon,Yim, Sang-Youp,Seo, Hyungtak,Jeon, Hyeongtag The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.28
<P>We demonstrate that a hybrid nanostructure consisting of a RuO<SUB>2</SUB> nanoparticle (NP)–ZnO nanorod confers dual local surface plasmon resonance (LSPR) enhancement of ultraviolet (UV) light emission and increase of visible light absorption. A RuO<SUB>2</SUB> NP–ZnO nanorod hybrid was fabricated by an atomic layer deposition method. The size and compositional control of the RuO<SUB>2</SUB> NP allowed (i) visible light absorption increase by the LSPR effect and (ii) proper interfacial electronic alignment of the RuO<SUB>2</SUB>–ZnO nanojunction, leading to LSPR coupling with UV light emission enhancement. Based on the combined LSPR effect factor, the dual functionality of LSPR was maximized with 10–20 nm sized RuO<SUB>2</SUB> NPs. These results suggest that a sophisticated design of the nanostructure material heterointerface enables LSPR enhancement of both light harvesting and emission.</P> <P>Graphic Abstract</P><P>A hybrid nanostructure consisting of a RuO<SUB>2</SUB> nanoparticle–ZnO nanorod grown by atomic layer deposition confers dual surface plasmon resonance enhancement of ultraviolet light emission and visible light absorption. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm31513k'> </P>
Bang, Seokhwan,Lee, Seungjun,Park, Joohyun,Park, Soyeon,Jeong, Wooho,Jeon, Hyeongtag Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.23
<P>Thin films of ZnO were deposited by atomic layer deposition (ALD) at different process temperatures and the resulting chemical and electrical characteristics were investigated. As the process temperature increased, the ZnO film exhibited an increase in carrier concentration from 1.3 × 10<SUP>15</SUP> to 2.1 × 10<SUP>19</SUP> cm<SUP>−3</SUP>, and a decrease in resistivity from 6.7 × 10<SUP>3</SUP> to 8.2 × 10<SUP>−3</SUP> Ω cm. We utilized this temperature dependence of the electrical properties and fabricated thin film transistors (TFTs) at different temperatures with both single and double channel layers. In the ZnO-TFT with a single channel layer, the overall device performance of the ZnO-TFT, such as the <I>I</I><SUB>on</SUB>/<I>I</I><SUB>off</SUB> ratio and subthreshold swing (SS), was degraded as the entire channel resistance decreased. In contrast, the ZnO-TFT with a double channel layer could control the turn-on voltage and threshold voltage by suppressing the increase in the off-current. The <I>I</I><SUB>on</SUB>/<I>I</I><SUB>off</SUB> ratios were 8.6 × 10<SUP>5</SUP>, 2.2 × 10<SUP>6</SUP> and 4.7 × 10<SUP>5</SUP> and the subthreshold swings exhibited 0.60 V/decade, 0.71 V/decade and 0.68 V/decade for the TFT with interface channel layers deposited at 120 °C, 140 °C and 160 °C, respectively. The saturation mobility slightly increased from 1.267 to 1.912 cm V<SUP>−1</SUP>s<SUP>−1</SUP> as the process temperature of the interface channel layer increased.</P>
Bang, Seokhwan,Lee, Seungjun,Ko, Youngbin,Park, Joohyun,Shin, Seokyoon,Seo, Hyungtak,Jeon, Hyeongtag Springer 2012 NANOSCALE RESEARCH LETTERS Vol.7 No.1
<P>We demonstrate the morphological control method of ZnO nanostructures by atomic layer deposition (ALD) on an Al<SUB>2</SUB>O<SUB>3</SUB>/ZnO seed layer surface and the application of a hierarchical ZnO nanostructure for a photodetector. Two layers of ZnO and Al<SUB>2</SUB>O<SUB>3</SUB> prepared using ALD with different pH values in solution coexisted on the alloy film surface, leading to deactivation of the surface hydroxyl groups. This surface complex decreased the ZnO nucleation on the seed layer surface, and thereby effectively screened the inherent surface polarity of ZnO. As a result, a 2-D zinc hydroxyl compound nanosheet was produced. With increasing ALD cycles of ZnO in the seed layer, the nanostructure morphology changes from 2-D nanosheet to 1-D nanorod due to the recovery of the natural crystallinity and polarity of ZnO. The thin ALD ZnO seed layer conformally covers the complex nanosheet structure to produce a nanorod, then a 3-D, hierarchical ZnO nanostructure was synthesized using a combined hydrothermal and ALD method. During the deposition of the ALD ZnO seed layer, the zinc hydroxyl compound nanosheets underwent a self-annealing process at 150 °C, resulting in structural transformation to pure ZnO 3-D nanosheets without collapse of the intrinsic morphology. The investigation on band electronic properties of ZnO 2-D nanosheet and 3-D hierarchical structure revealed noticeable variations depending on the richness of Zn-OH in each morphology. The improved visible and ultraviolet photocurrent characteristics of a photodetector with the active region using 3-D hierarchical structure against those of 2-D nanosheet structure were achieved.</P>
Al<sub>2</sub>O<sub>3</sub> buffer in a ZnO thin film transistor with poly-4-vinylphenol dielectric
Bang, Seokhwan,Lee, Seungjun,Jeon, Sunyeol,Kwon, Semyung,Jeong, Wooho,Kim, Honggyu,Shin, Iksup,Chang, Ho Jung,Park, Hyung-ho,Jeon, Hyeongtag Institute of Physics 2009 Semiconductor science and technology Vol.24 No.2
<P>We compared the characteristics of bottom-gate ZnO-thin film transistors using poly-4-vinylphenol (PVP) and PVP/Al<SUB>2</SUB>O<SUB>3</SUB> dielectrics. The PVP dielectric is more hydrophobic than the PVP/Al<SUB>2</SUB>O<SUB>3</SUB> dielectric and is not useful for TFT devices because of its high leakage current density, but this leakage current density can be significantly reduced by inserting Al<SUB>2</SUB>O<SUB>3</SUB>. We deposited ZnO and Al<SUB>2</SUB>O<SUB>3</SUB> films by atomic layer deposition (ALD) because it is a low-temperature process. The ZnO-TFTs with either a PVP or a PVP/Al<SUB>2</SUB>O<SUB>3</SUB> dielectric exhibit typical field-effect transistor characteristics with n-channel properties. The ZnO-TFT containing PVP/Al<SUB>2</SUB>O<SUB>3</SUB> exhibits clear pinch-off and excellent saturation with an enhanced mode operation. The on/off ratio of 7.9 × 10<SUP>4</SUP> for the device containing the hybrid dielectric is about three orders of magnitude higher than the ratio of 47 for the device containing PVP. The subthreshold gate swings are 12 V/decade for the TFT containing PVP and 1.2 V/decade for the TFT containing PVP/Al<SUB>2</SUB>O<SUB>3</SUB>. The density of the interface trap state is significantly lower in the device containing PVP/Al<SUB>2</SUB>O<SUB>3</SUB> than in the ZnO-TFT containing PVP. The saturation mobility was 0.05 and 0.8 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, respectively, in the TFTs containing PVP and PVP/Al<SUB>2</SUB>O<SUB>3</SUB>.</P>
A study on H<sub>2</sub> plasma treatment effect on a-IGZO thin film transistor
Kim, Jihoon,Bang, Seokhwan,Lee, Seungjun,Shin, Seokyoon,Park, Joohyun,Seo, Hyungtak,Jeon, Hyeongtag Cambridge University Press (Materials Research Soc 2012 Journal of materials research Vol.27 No.17
<▼1><B>Abstract</B><P/></▼1><▼2><P>We report the effect of H2 plasma treatment on amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT). The changes in electrical characteristics and stability of the a-IGZO TFT treated by H2 plasma were evaluated under thermal stress. Each device exhibited a change in the subthreshold swing, turn on voltage shift, and hysteresis depending on the amount of hydrogen atom. It was found that there occurred a decrease of oxygen deficiency and an increase of hydrogen content in channel layer and channel/dielectric interface with increasing treatment time. The proper hydrogen dose well passivated the oxygen vacancies; however, more hydrogen dose acted as excessive donors. The change of oxygen vacancy and total trap charge were explained by the activation energy from Arrhenius plot. Through this study, we found that the optimized H2 plasma treatment brings device stability by affecting oxygen vacancy and trap content in channel bulk and channel/dielectric interface.</P></▼2>
Characteristics of the ZnO thin film transistor by atomic layer deposition at various temperatures
Kwon, Semyung,Bang, Seokhwan,Lee, Seungjun,Jeon, Sunyeol,Jeong, Wooho,Kim, Hyungchul,Gong, Su Cheol,Chang, Ho Jung,Park, Hyung-ho,Jeon, Hyeongtag Institute of Physics 2009 Semiconductor science and technology Vol.24 No.3
<P>ZnO thin films were deposited by atomic layer deposition (ALD) at various temperatures and the resulting electrical and chemical properties were examined. The fraction of O–H bonds in ZnO films decreased from 0.39 to 0.24 with increasing processing temperatures. The O/Zn ratio decreased from 0.90 at 70 °C to 0.78 at 130 °C. The carrier concentration and resistivity changed sharply with decreasing temperature. The ZnO thin film transistors (TFTs) were fabricated at processing temperatures of 70 to 130 °C and the electrical properties of the TFT were as follows: the field-effect mobility ranged from 8.82 × 10<SUP>−3</SUP> to 6.11 × 10<SUP>−3</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, the on/off current ratio ranged from 1.28 × 10<SUP>6</SUP> to 2.43 × 10<SUP>6</SUP>, the threshold voltage ranged from −12.5 to 14.7 V and the subthreshold swing ranged from 1.21 to 24.1 V/decade. The electrical characteristics of the ZnO TFT were enhanced as the processing temperature decreased.</P>