GaAsSe Ternary Alloy Nanowires for Enhanced Photoconductivity

Park, Kidong,Lee, Jinha,Kim, Doyeon,Seo, Jaemin,Lee, Jung Ah,Kwak, In Hye,Kwon, Ik Seon,Ahn, Jae Pyoung,Park, Jeunghee American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.6

<P>Alloyed semiconductor nanowires (NWs) are of great interest for next-generation integrated optoelectronic nanodevices owing to their tunable band gap and emission wavelength. In this study, we synthesized the GaAsSe ternary alloy nanowires (NWs) with various compositions between GaAs and Ga<SUB>2</SUB>Se<SUB>3</SUB> using chemical vapor transport method. The band gap was continuously tuned in the range of 1.5-2.1 eV because of the completely miscible solid solution at all compositions. The alloy NWs (including Ga<SUB>2</SUB>Se<SUB>3</SUB>) consisted of a cubic phase with the [011] growth direction, in contrast with the GaAs NWs grown along the [111] direction. In particular, the GaAs<SUB>1-<I>x</I></SUB>Se<SUB><I>x</I></SUB> (<I>x</I> = 0.3) alloy NWs were grown from Ga-rich Au nanoparticles such as cubic-phase AuGa<SUB>2</SUB> and had a defect-free single-crystalline nature. X-ray photoelectron spectroscopy analysis reveals much less surface oxide layers for <I>x</I> = 0.3, suggesting that Se incorporation at this composition effectively diminishes the surface defects. We fabricated photodetectors using the individual NW, showing that the photocurrent decreases with the increasing Se composition. The alloy composition significantly diminished the dark current and thus greatly enhanced the photosensitivity for <I>x</I> = 0.3.</P> [FIG OMISSION]</BR>

Convenient metal embedment into mesoporous silica channels for high catalytic performance in AB dehydrogenation

Park, Jin-Hyung,Kim, Sung-Kwan,Kim, Han Sung,Cho, Yong Jae,Park, Jeunghee,Lee, Kyung Eun,Yoon, Chang Won,Nam, Suk Woo,Kang, Sang Ook The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.92

<P>The infiltration of palladium nanoparticles (PdNPs) into the channels of SBA-15 was conveniently achieved <I>via</I> an incipient wetness procedure employing a tetraglyme solution. Electron tomography demonstrated that PdNPs were outgrown preferentially from the channels. The resultant Pd/SBA-15 showed high performance in the dehydrogenation kinetics of ammonia borane.</P> <P>Graphic Abstract</P><P>The infiltration of palladium nanoparticles into the channels of mesoporous silica was conveniently achieved <I>via</I> an incipient wetness procedure employing a tetraglyme solution. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc46758a'> </P>

GaP–ZnS Pseudobinary Alloy Nanowires

Park, Kidong,Lee, Jung Ah,Im, Hyung Soon,Jung, Chan Su,Kim, Han Sung,Park, Jeunghee,Lee, Chang-Lyoul American Chemical Society 2014 NANO LETTERS Vol.14 No.10

<P>Multicomponent nanowires (NWs) are of great interest for integrated nanoscale optoelectronic devices owing to their widely tunable band gaps. In this study, we synthesize a series of (GaP)(1x)(ZnS)(x) (0 = x = 1) pseudobinary alloy NWs using the vapor transport method. Compositional tuning results in the phase evolution from the zinc blende (ZB) (x < 0.4) to the wurtzite (WZ) phase (x > 0.7). A coexistence of ZB and WZ phases (x = 0.40.7) is also observed. In the intermediate phase coexistence range, a coreshell structure is produced with a composition of x = 0.4 and 0.7 for the core and shell, respectively. The band gap (2.43.7 eV) increases nonlinearly with increasing x, showing a significant bowing phenomenon. The phase evolution leads to enhanced photoluminescence emission. Strikingly, the photoluminescence spectrum shows a blue-shift (70 meV for x = 0.9) with increasing excitation power, and a wavelength-dependent decay time. Based on the photoluminescence data, we propose a type-II pseudobinary heterojunction band structure for the single-crystalline WZ phase ZnS-rich NWs. The slight incorporation of GaP into the ZnS induces a higher photocurrent and excellent photocurrent stability, which opens up a new strategy for enhancing the performance of photodetectors.</P>

Quantum Dots Formed in Three-dimensional Dirac Semimetal Cd₃As₂ Nanowires

Jung, Minkyung,Yoshida, Kenji,Park, Kidong,Zhang, Xiao-Xiao,Yesilyurt, Can,Siu, Zhuo Bin,Jalil, Mansoor B. A.,Park, Jinwan,Park, Jeunghee,Nagaosa, Naoto,Seo, Jungpil,Hirakawa, Kazuhiko American Chemical Society 2018 NANO LETTERS Vol.18 No.3

<P>We demonstrate quantum dot (QD) formation in three-dimensional Dirac semimetal Cd<SUB>3</SUB>As<SUB>2</SUB> nanowires using two electrostatically tuned p-n junctions with a gate and magnetic fields. The linear conductance measured as a function of gate voltage under high magnetic fields is strongly suppressed at the Dirac point close to zero conductance, showing strong conductance oscillations. Remarkably, in this regime, the Cd<SUB>3</SUB>As<SUB>2</SUB> nanowire device exhibits Coulomb diamond features, indicating that a clean single QD forms in the Dirac semimetal nanowire. Our results show that a p-type QD can be formed between two n-type leads underneath metal contacts in the nanowire by applying gate voltages under strong magnetic fields. Analysis of the quantum confinement in the gapless band structure confirms that p-n junctions formed between the p-type QD and two neighboring n-type leads under high magnetic fields behave as resistive tunnel barriers due to cyclotron motion, resulting in the suppression of Klein tunneling. The p-type QD with magnetic field-induced confinement shows a single hole filling. Our results will open up a route to quantum devices such as QDs or quantum point contacts based on Dirac and Weyl semimetals.</P> [FIG OMISSION]</BR>

Thickness-dependent bandgap and electrical properties of GeP nanosheets

Kim, Doyeon,Park, Kidong,Shojaei, Fazel,Debela, Tekalign Terfa,Kwon, Ik Seon,Kwak, In Hye,Seo, Jaemin,Ahn, Jae Pyoung,Park, Jeunghee,Kang, Hong Seok The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.27

<P>Recently there have been extensive efforts to develop novel two-dimensional (2D) layered structures, owing to their fascinating thickness-dependent optical/electrical properties. Herein, we synthesized thin GeP nanosheets that had a band gap (<I>E</I>g) of 2.3 eV, which is a dramatic increase from the value in the bulk (0.9 eV) upon exfoliation. This <I>E</I>g value is close to that of the GeP monolayer predicted by first-principles calculations (HSE06 functional). The calculations also indicate a strong dependence of <I>E</I>g on the number of layers (2.306, 1.660, 1.470, and 1.397 eV for mono-, bi-, tri-, and tetralayers, respectively), and that the band edge positions are suitable for water splitting reactions. Field-effect transistor devices were fabricated using the p-type GeP nanosheets of various thicknesses, and the devices demonstrated a significant decrease in the hole mobility but an increased on-off ratio as the layer number decreased. The larger on-off ratio (10<SUP>4</SUP>) for the thinner ones is promising for use in novel 2D (photo)electronic nanodevices. Further, liquid-exfoliated GeP nanosheets (thickness = 1-2 nm) deposited on Si nanowire arrays can function as a promising photoanode for solar-driven water-splitting photoelectrochemical (PEC) cells. Based on the calculated band offset with respect to the Fermi levels for the two half-reactions in the water splitting reaction, the performance of the PEC cell can be explained by the formation of an effective p-GeP/n-Si heterojunction.</P>

Large Scale Synthesis of Highly Pure Single Crystalline Tellurium Nanowires by Thermal Evaporation Method

Mohanty, Paritosh,Park, Jeunghee,Kim, Bongsoo American Scientific Publishers 2006 Journal of nanoscience and nanotechnology Vol.6 No.11

<P>Single crystalline tellurium nanowires were successfully synthesized in large scale by a facile approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a Si substrate. Tellurium was evaporated by heating at 300° C at 1 torr and condensed on the Si substrate at 100-150° C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 30 min. The as-synthesized nanowires have diameters between 100-300 nm and lengths up to several micrometers. The single crystalline nanowires grew in a preferred [0001] direction. The obtained nanowires were highly pure as only tellurium metal was used in the vaporization process, and no other reagent, surfactant, or template were used for the growth. This low temperature and high-yield approach to the tellurium nanowires synthesis may facilitate its industrial production for various applications.</P>

Fabrication of Single Crystalline Cadmium Nanowires by a Facile Low Temperature Vapor Phase Method

Mohanty, Paritosh,Park, Jeunghee,Lee, Gangho,Kim, Bongsoo American Scientific Publishers 2006 Journal of nanoscience and nanotechnology Vol.6 No.11

<P>Single-crystalline cadmium nanowires were successfully fabricated by vaporization of cadmium metal powders in a horizontal quartz tube furnace at 250 °C. The vaporization was carried out for 30 minutes and yielded nanowires of diameters of 80 to 250 nm and lengths up to several tens of microns. The nanowires were deposited on a Si (111) substrate kept at the lower temperature zone (150-175 °C) of the furnace. When the deposition temperature was lower than this, hexagonal nanodisks were produced. The possible mechanism for the formation of the obtained nanostructures is discussed.</P>

Temperaure dependent growth of carbon nanotubes

Yun Tack Lee,Jeunghee Park,Hyun Ryu,Hwack Joo Lee 한국진공학회 2002 한국진공학회 학술발표회초록집 Vol.- No.-

Photoluminescence and Photocurrents of GaS_1–<i>x</i>Se_<i>x</i> Nanobelts

Jung, Chan Su,Park, Kidong,Shojaei, Fazel,Oh, Jin Young,Im, Hyung Soon,Lee, Jung Ah,Jang, Dong Myung,Park, Jeunghee,Myoung, NoSung,Lee, Chang-Lyoul,Lee, Jong Woon,Song, Jae Kyu,Kang, Hong Seok American Chemical Society 2016 Chemistry of materials Vol.28 No.16

<P>Two-dimensional layered structures have recently drawn worldwide attention because of their intriguing optical and electrical properties. GaS and GaSe are attractive layered materials owing to their wide band gap. Herein, we synthesized GaS1-xSex belt-type multilayers (nanobelts) with uniform morphology ([2110] hexagonal-phase long axis) by a chemical vapor transport method, and investigate their composition-dependent optical and optoelectronic properties. The GaS1-xSex exhibited strong visible-range photoluminescence at 490-620 nm (2.0-2.5 eV), with a unique composition dependence: longer decay time for the S-rich compositions (x <= 0.5). Photocurrent measurements were performed on individual nanobelts by fabricating photodetector devices; higher photocurrents were found for x <= 0.5. First-principles calculations predicted that oxygen chemisorption can cause the direct and indirect band gaps of GaS to converge, similar to the band structures of GaSe, and thus enhance the optical properties. On the basis of the band alignment (predicted by calculation) for the Schottky barriers in the metal-semiconductor metal photodetector, we proposed the origin of the higher photocurrent for GaS than for GaSe.</P>

Zn₃P₂–Zn₃As₂ Solid Solution Nanowires

Im, Hyung Soon,Park, Kidong,Jang, Dong Myung,Jung, Chan Su,Park, Jeunghee,Yoo, Seung Jo,Kim, Jin-Gyu American Chemical Society 2015 NANO LETTERS Vol.15 No.2

<P>Semiconductor alloy nanowires (NWs) have recently attracted considerable attention for applications in optoelectronic nanodevices because of many notable properties, including band gap tunability. Zinc phosphide (Zn3P2) and zinc arsenide (Zn3As2) belong to a unique pseudocubic tetragonal system, but their solid solution has rarely been studied. Here In this study, we synthesized composition-tuned Zn-3(P1-xAsx)(2) NWs with different crystal structures by controlling the growth conditions during chemical vapor deposition. A first type of synthesized NWs were single-crystalline and grew uniformly along the [110] direction (in a cubic unit cell) over the entire compositional range (0 <= x <= 1) explored. The use of an indium source enabled the growth of a second type of NWs, with remarkable cubic-hexagonal polytypic twinned superlattice and bicrystalline structures. The growth direction of the Zn3P2 and Zn3As2 NWs was also switched to [111] and [112], respectively. These structural changes are attributable to the Zn-depleted indium catalytic nanoparticles which favor the growth of hexagonal phases. The formation of a solid solution at all compositions allowed the continuous tuning of the band gap (1.0-1.5 eV). Photocurrent measurements were performed on individual NWs by fabricating photodetector devices; the single-crystalline NWs with [110] growth direction exhibit a higher photoconversion efficiency compared to the twinned crystalline NWs with [111] or [112] growth direction.</P>