Double-row transport in quantum wires of shallow confinement

Hew, W.K.,Thomas, K.J.,Pepper, M.,Farrer, I.,Anderson, D.,Jones, G.A.C.,Ritchie, D.A. North-Holland 2010 Physica E, Low-dimensional systems & nanostructure Vol.42 No.4

The bifurcation of the electron system in a quantum wire has been observed in the form of the suppression and disappearance of the quantised conductance plateau at 2e<SUP>2</SUP>/h. We now present low-temperature transport measurements of a top-gated split-gate quantum wire that serve to further characterise this double-row regime of transport. A small distortion of the confinement caused by asymmetrical biasing of the split gates gives rise to a radical change in the conductance characteristics of the wire, beginning with the introduction of a plateau at G=e<SUP>2</SUP>/h which rises to around 0.7x2e<SUP>2</SUP>/h with greater differential bias between the split gates. DC source-drain bias measurements in this regime show a split zero-bias peak at low conductances merging into a single peak around G=0.7xe<SUP>2</SUP>/h, which then persists up to the plateau at 4e<SUP>2</SUP>/h.

Optimization of Hole Injection and Transport Layers for High-Performance Quantum-Dot Light-Emitting Diodes

신재승,유종훈,허수빈,강성준 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.12

High-luminance, efficient quantum-dot light-emitting diodes (QLEDs) have been achieved by optimizing the balance between the hole injection layer (HIL) and the hole transport layer (HTL). Different concentrations of vanadium oxide (V$_2$O$_5$) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(4-sec-butylphenyl)diphenylamine)] (TFB) solutions were used to form the efficient HIL and HTL, respectively, for the QLEDs. The hole injection and transport behavior was characterized by using hole-only devices (HODs). The QLEDs, which were prepared with 0.5 wt.\% of V$_2$O$_5$ and 0.1 wt.\% of TFB as HIL and HTL, respectively, showed a maximum current efficiency of 2.27 cd$\cdot$A$^{-1}$ and a maximum luminance of 71,260 cd$\cdot$m$^{-2}$. Moreover, the turn-on voltage of the device was as low as 2.2 V due to the efficient carrier injection and transport. The results provide useful information for fabricating high-performance QLEDs.

Highly efficient and low turn-on voltage quantum-dot light-emitting diodes using a ZnMgO/ZnO double electron transport layer

허수빈,신재승,김태연,박성호,정운호,김현준,홍종암,김범수,박용섭,최병두,김종규,강성진 한국물리학회 2021 Current Applied Physics Vol.29 No.-

A ZnMgO and ZnO double-layered structure was prepared to create a stepwise interfacial electronic structure to improve the electron-injection and electron-transport behaviors in quantum-dot light-emitting diodes (QLEDs). The current density of the electron-only device (EOD) with ZnMgO/ZnO was higher than that of the EOD with only ZnMgO. The detailed QLED interfacial electronic structure was measured using X-ray and ultraviolet photoelectron spectroscopy. A stepwise interfacial electronic structure for electron injection and electron transport was observed connecting the aluminum cathode to the ZnMgO conduction band minimum (CBM) via the ZnO CBM. The QLEDs with the ZnMgO/ZnO double electron transport layer showed an improved performance, with a maximum luminance and current efficiency of 90,892 cd m 2 and 19.2 cd A 1, respectively. Moreover, the turn-on voltage of the device was significantly reduced to 2.6 V due to the stepwise interfacial electronic structure between the aluminum cathode and ZnMgO CBM. This research provides a useful method for developing highly efficient and low turn-on voltage QLEDs using a ZnMgO/ZnO double ETL for next-generation display.

Carrier transport of inverted quantum dot LED with PEIE polymer

Son, D.I.,Kim, H.H.,Cho, S.,Hwang, D.K.,Seo, J.W.,Choi, W.K. Elsevier Science 2014 ORGANIC ELECTRONICS Vol.15 No.4

An inverted-type quantum-dot light-emitting-diode (QD LED), employing low-work function organic material polyethylenimine ethoxylated (PEIE) as electron injection layer, was fabricated by all solution processing method, excluding anode electrode. From transmission electron microscopy (TEM) and scanning electron microscopy (SEM) studies, it was confirmed that CdSe@ZnS QDs with 7nm size were uniformly distributed as a monolayer on PEIE layer. In this inverted QD LED, two kinds of hybrid organic materials, [poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo)(F8BT)+poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine (poly-TPD)] and [4,4'-N,N'-dicarbazole-biphenyl (CBP)+poly-TPD], were adopted as hole transport layer having high highest occupied molecular orbital (HOMO) level for improving hole transport ability. At a low-operating voltage of 8V, the device emits orange and red spectral radiation with high brightness up to 2450 and 1420cd/m<SUP>2</SUP>, and luminance efficacy of 1.4cd/A and 0.89cd/A, respectively, at 7V applied bias. Also, the carrier transport mechanisms for the QD LEDs are described by using several models to fit the experimental I-V data.

이차원 양자 효과를 고려한 극미세 Double-Gate MOSFET 특성 분석

김지현(Jihyun Kim),손애리(Aeri Son),정나래(Narae Jeong),신형순(Hyungsoon Shin) 대한전자공학회 2008 電子工學會論文誌-SD (Semiconductor and devices) Vol.45 No.10

기존의 MOSFET는 단채널 현상의 증가로 인하여 스케일링에 한계를 가지고 있다. Double-Gate MOSFET (DG-MOSFET)는 소자의 길이가 축소되면서 나타나는 단채널 현상을 효과적으로 제어하는 차세대 소자이다. DG-MOSFET으로 소자를 축소시키면 채널 길이가 10nm 이하에서 게이트 방향뿐만 아니라 소스와 드레인 방향에서도 양자 효과가 발생한다. 또한 게이트 길이가 매우 짧아지면 ballistic transport 현상이 발생한다. 따라서 본 연구에서는 2차원 양자 효과와 ballistic transport를 고려하여 DG-MOSFET의 특성을 분석하였다. 또한 단채널 효과를 줄이기 위해서 tsi와 underlap 그리고 lateral doping gradient를 이용하여 소자 구조를 최적화하였다. The bulk-planer MOSFET has a scaling limitation due to the short channel effect (SCE). The Double-Gate MOSFET (DG-MOSFET) is a next generation device for nanoscale with excellent control of SCE. The quantum effect in lateral direction is important for subthreshold characteristics when the effective channel length of DG-MOSFET is less than 10nm, Also, ballistic transport is getting important. This study shows modeling and design issues of nanoscale DG-M OSFET considering the 2D quantum effect and ballistic transport. We have optimized device characteristics of DG-MOSFET using a proper value of tsi, underlap and lateral doping gradient.

Fano-Andreev Transport and Circulating Currents in Mesoscopic Interferometers

Yao Heng Su,Sam Young Cho 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3

Quantum correlation and interference effects are investigated in mesoscopic interferometers connected to a normal metal and a superconductor. For quasiparticle excitation energies smaller than superconducting gap, a Fano-Andreev antiresonance for zero excitation energy is shown to be split into two zero-transmissions located at energies lower and higher than the Fano-Andreev antiresonance energy. For an excitation energy bigger than the gap, the higher energy antiresonance disappears for electron-like quasiparticle transport. In the presence of a superconductor interface potential <i>Z</i>, we find that the transport and the circulating currents normalized by their amplitudes for a clean interface have the same <i>I</i>(<i>Z</i>)-<i>Z</i> curve. We discuss a transition among the three types of normalized currents, which shows a characteristic transition diagram in association with the excitation energy. Also, as a demonstration of the existence of Andreev holes, we show that only the Andreev hole current can circulate along the interferometer loop.

Variation of the Carrier Lifetime Across the Ground-state Band of Ensemble Quantum Dots: An Indication for Quantum-dot Characteristics at High Temperatures

Chengshou An,장유동,이동한 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.1

High-temperature characteristics of InAs/GaAs quantum dots (QDs) with well-separated ground and excited state photoluminescence peaks were studied by time-resolved photoluminescence. The carrier lifetime across the ground state band of the ensemble QDs showed a large variation (> 2ns) at 250 K while the lifetimes were almost the same at low temperatures. The large variation in the carrier lifetime, shorter at the high energy side and longer at the low energy side, is a clear indication of carrier transport from smaller QDs to larger QDs via the wetting layer. The variation is a good indicator to determine whether the QD characteristics are remained at high temperatures,which is important for device applications.

Two-step annealed CdS/CdSe co-sensitizers for quantum dot-sensitized solar cells

Sung Woo Jung,Min-A Park,김재홍,김현수,최철종,Soon Hyung Kang,안광순 한국물리학회 2013 Current Applied Physics Vol.13 No.7

CdS/CdSe co-sensitizers on TiO2 films were annealed using a two-step procedure; high temperature (300 ℃) annealing of TiO2/CdS quantum dots (QDs), followed by low temperature (150 ℃) annealing after the deposition of CdSe QDs on the TiO2/CdS. For comparison, two types of films were prepared; CdS/CdSe-assembled TiO2 films conventionally annealed at a single temperature (150 or 300 ℃) and nonannealed films. The 300 ℃-annealed TiO2/CdS/CdSe showed severe coalescence of CdSe QDs, leading to the blocked pores and hindered ion transport. The QD-sensitized solar cell (QD-SSC) with the 150 ℃ annealed TiO2/CdS/CdSe exhibited better overall energy conversion efficiency than that with the nonannealed TiO2/CdS/CdSe because the CdSe QDs annealed at a suitable temperature (150 ℃) provided better light absorption over long wavelengths without the hindered ion transport. The QD-SSC using the two-step annealed TiO2/CdS/CdSe increased the cell efficiency further, compared to the QD-SSC with the 150 ℃-annealed TiO2/CdS/CdSe. This is because the 300 ℃-annealed, highly crystalline CdS in the twostep annealed TiO2/CdS/CdSe improved electron transport through CdS, leading to a significantly hindered recombination rate.

Two-step annealed CdS/CdSe co-sensitizers for quantum dot-sensitized solar cells

Jung, S.W.,Park, M.A.,Kim, J.H.,Kim, H.,Choi, C.J.,Kang, S.H.,Ahn, K.S. Elsevier 2013 Current Applied Physics Vol.13 No.7

CdS/CdSe co-sensitizers on TiO<SUB>2</SUB> films were annealed using a two-step procedure; high temperature (300 <SUP>o</SUP>C) annealing of TiO<SUB>2</SUB>/CdS quantum dots (QDs), followed by low temperature (150 <SUP>o</SUP>C) annealing after the deposition of CdSe QDs on the TiO<SUB>2</SUB>/CdS. For comparison, two types of films were prepared; CdS/CdSe-assembled TiO<SUB>2</SUB> films conventionally annealed at a single temperature (150 or 300 <SUP>o</SUP>C) and non-annealed films. The 300 <SUP>o</SUP>C-annealed TiO<SUB>2</SUB>/CdS/CdSe showed severe coalescence of CdSe QDs, leading to the blocked pores and hindered ion transport. The QD-sensitized solar cell (QD-SSC) with the 150 <SUP>o</SUP>C-annealed TiO<SUB>2</SUB>/CdS/CdSe exhibited better overall energy conversion efficiency than that with the non-annealed TiO<SUB>2</SUB>/CdS/CdSe because the CdSe QDs annealed at a suitable temperature (150 <SUP>o</SUP>C) provided better light absorption over long wavelengths without the hindered ion transport. The QD-SSC using the two-step annealed TiO<SUB>2</SUB>/CdS/CdSe increased the cell efficiency further, compared to the QD-SSC with the 150 <SUP>o</SUP>C-annealed TiO<SUB>2</SUB>/CdS/CdSe. This is because the 300 <SUP>o</SUP>C-annealed, highly crystalline CdS in the two-step annealed TiO<SUB>2</SUB>/CdS/CdSe improved electron transport through CdS, leading to a significantly hindered recombination rate.

Quantum-interference-induced Magnetization in Mesoscopic Loop Interferometers

Hai Tao Wang,Sam Young Cho,Taeseung Choi 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.10

We theoretically investigate quantum interference effects in mesoscopic loop interferometers. In the absence of an Aharonov-Bohm flux, the asymmetry of the arm length of the interferometer can induce a magnetic polarization current circulating along the interferometer loop. We clarify the existing regions of magnetic polarization current in terms of the dimensionless wavevector and a parameter for the asymmetric arm lengths. The magnetic polarization current is found to have a periodic diamond structure that can be characterized by magnetic and non-magnetic diamond zones. The applied magnetic flux develops a concave diamond-shaped non-magnetic region inside the magnetic diamond zones. When the magnetic flux varies across Φ= (2n + 1)π/2, with n being an integer, the magnetic diamond zone becomes a non-magnetic diamond zone and vice versa. In addition, the unique behaviors of the transport current flowing through the interferometer are discussed in association with the magnetic polarization current circulating along the interferometer loop. Finally, the magnetic moments induced at a finite bias are shown to be sufficiently large to be observed experimentally.