• Applied Science and Convergence Technology
• /
• 제26권3호
• /
• pp.47-49
• /
• 2017

Photocurrent enhancement has been investigated in monolayer (1L) $MoS_2$ with PbS quantum dots (QDs). A metal-semiconductor-metal (Au-1L $MoS_2$-Au) junction device is fabricated using a standard photolithography method. Considerably improved photo-electrical properties are obtained by coating PbS QDs on the Au-1L $MoS_2$-Au device. Time dependent photoconductivity and current-voltage characteristics are investigated. For the QDs-coated $MoS_2$ device, it is observed that the photocurrent is considerably enhanced and the decay life time becomes longer. We propose that carriers in QDs are excited and transferred to the $MoS_2$ channel under light illumination, improving the photocurrent of the 1L $MoS_2$ channel. Our experimental findings suggest that two-dimensional layered semiconductor materials combined with QDs could be used as building blocks for highly-sensitive optoelectronic detectors including radiation sensors.

• Carbon letters
• /
• 제16권3호
• /
• pp.211-214
• /
• 2015

Bio-imaging and drug carriers for delivery have created a huge demand for crystals. Crystals are fascinating materials that have been grown for a long time but obtaining biocompatible fluorescent crystals is a challenging task. We report on the growth of fluorescent crystals using a carbon dot (C-dot) solution by a hydrothermal process. The crystallization pattern of these C-dots exhibited a unique dendritic structure having a feather-like morphology. The growth temperature and pressure were maintained at 60℃ and 200 mmHg, respectively, for crystal growth. A green fluorescence (under UV light) that was observed in the C-dot solution was retained in the crystals formed from the solution. Cytotoxicity studies on Vero cells revealed the crystals to be extremely biocompatible. These fluorescent crystals are extremely well suited for biomedical and optoelectronic applications.

• ETRI Journal
• /
• 제21권4호
• /
• pp.65-82
• /
• 1999

We present a calculation model for an improved quantitative theoretical analysis of electronic and optical properties of strained-piezoelectric[111] InGaAs/GaAs superlattices (SLs). The model includes a full band-coupling between the four important energy bands: conduction, heavy, light, and spin split-off valence bands. The interactions between these and higher lying bands are treated by the k ${\cdot}$ p perturbation method. The model takes into account the differences in the band and strain parameters of constituent materials of the heterostructures by transforming it into an SL potential in the larger band-gap material region. It self-consistently solves an $8{\times}8$ effective-mass $Schr{\ddot{o}}dinger$ equation and the Hartree and exchange-correlation potential equations through the variational procedure proposed recently by the present first author and applied to calculate optical matrix elements and spontaneous emission rates. The model can be used to further elucidate the recent theoretical results and experimental observations of interesting properties of this type of quantum well and SL structures, including screening of piezoelectric field and its resultant optical nonlinearities for use in optoelectronic devices.

• Journal of Magnetics
• /
• 제20권4호
• /
• pp.347-352
• /
• 2015

The magnetoelectric (ME) characteristics for Terfenol-D/PZT laminate composite dependence on bias magnetic field is investigated. At low frequency, ME response is determined by the piezomagnetic coefficient $d_{33,m}$ and the elastic compliance $s_{33}^H$ of magnetostrictive material, $d_{33,m}$ and $s_{33}^H$ for Terfenol-D are inherently nonlinear and dependent on $H_{dc}$, leading to the influence of $H_{dc}$ on low-frequency ME voltage coefficient. At resonance, the mechanical quality factor $Q_m$ dependences on $H_{dc}$ results in the differences between the low-frequency and resonant ME voltage coefficient with $H_{dc}$. In terms of ${\Delta}E$ effect, the resonant frequency shift is derived with respect to the bias magnetic field. Considering the nonlinear effect of magnetostrictive material and $Q_m$ dependence on $H_{dc}$c, it predicts the low-frequency and resonant ME voltage coefficients as a function of the dc bias magnetic field. A good agreement between the theoretical results and experimental data is obtained and it is found that ME characteristics dependence on $H_{dc}$ are mainly influenced by the nonlinear effect of magnetostrictive material.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
• /
• pp.134.2-134.2
• /
• 2014

Photonic crystal solar cells have the potential for addressing the disparate length scales in polymer photovoltaic materials, thereby confronting the major challenge in solar cell technology: efficiency. One must achieve simultaneously an efficient absorption of photons with effective carrier extraction. Unfortunately the two processes have opposing requirements. Efficient absorption of light calls for thicker PV active layers whereas carrier transport always benefits from thinner ones, and this dichotomy is at the heart of an efficiency/cost conundrum that has kept solar energy expensive relative to fossil fuels. This dichotomy persists over the entire solar spectrum but increasingly so near a semiconductor's band edge where absorption is weak. We report a 2-D, photonic crystal morphology that enhances the efficiency of organic photovoltaic cells relative to conventional planar cells. The morphology is developed by patterning an organic photoactive bulk heterojunction blend of Poly(3-(2-methyl-2-hexylcarboxylate) thiophene-co-thiophene) and PCBM via PRINT, a nano-embossing method that lends itself to large area fabrication of nanostructures. The photonic crystal cell morphology increases photocurrents generally, and particularly through the excitation of resonant modes near the band edge of the organic PV material. The device performance of the photonic crystal cell showed a nearly doubled increase in efficiency relative to conventional planar cell designs. Photonic crystals can also enhance performance of other optoelectronic devices including organic laser.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제40회 동계학술대회 초록집
• /
• pp.336-336
• /
• 2011

Over the past decades, organic semiconductors have been investigated intensely for their potential in a wide range of optoelectronic device applications since the organic materials have advantages for very light, flexible and low cost device fabrications. In this study, we fabricated small-molecule organic solar cells (OSCs) based on chloro[subphthalocyaninato]boron(III) (SubPc) as an electron donor and $C_{60}$ as an electron acceptor material. Recently SubPc, a cone-shaped molecule with $14{\pi}$-electrons in its aromatic system, has attracted growing attention in small-molecule OSC applications as an electron-donating material for its greater open-circuit voltage (VOC), extinction coefficient and dielectric constant compared to conventional planar metal phthalocyanines. In spite of the power conversion efficiency (PCE) enhancement of small-molecule OSC using SubPc and $C_{60}$, however, the study on the interface between donor-acceptor heterojunction of this system is limited. In this work, SubPc thin films at various thicknesses were deposited by organic molecular beam deposition (OMBD) and the evolution of surface morphology was observed using atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM). We also investigated the influence of film thickness and surface morphology on the PCE of small-molecule OSC devices.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 C
• /
• pp.446-448
• /
• 2000

Organic semiconductors based on vacuum-deposited films of fused-ring polycyclic aromatic hydrocarbon have great potential to be utilized as an active layer for electronic and optoelectronic devices. In this study, pentacene thin films and electrode materials were deposited by Organic Molecular Beam Deposition (OMBD) and vacuum evaporation respectively. For the gate dielectric layer, OPTMER PC403 photo acryl (JSR Coporation.) was spin-coated and cured at $220^{\circ}C$. Electrical characteristics of the devices were investigated, where the channel length and width was $50{\mu}m$ and 5 mm. It was found that field effect mobility was $0.039\;cm^2V^{-1}s^{-1}$, threshold voltage was -7 V, and on/off current ratio was $10^6$.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
• /
• pp.462-462
• /
• 2013

Gallium Oxide (Ga2O3) has been widely investigated for the optoelectronic applications due to its wide bandgap and the optical transparency. Recently, with the development of fabrication techniques in nanometer scale semiconductor materials, there have been an increasing number of extensive reports on the synthesis and characterization of Ga2O3 nano-structures such as nano-wires, nanobelts, and nano-dots. In contrast to typical vaporliquid-solid growth mode with metal catalysts to synthesis 1-dimensional nano-wires, there are several difficulties in fabricating the nanostructures by using sputtering techniques. This is attributed to the fact that relatively low growth temperatures and higher growth rate compared with chemical vapor deposition method. In this study, Ga2O3 chestnut burr were synthesized by using radio-frequency magnetron sputtering method. In contrast to typical sputtering method with sintered ceramic target, a Ga2O3 powder (99.99% purity) was used as a sputtering target. Several samples were prepared with varying the growth parameters, especially he growth time and the growth temperature to investigate the growth mechanism. Samples were characterized by using XRD, SEM, and PL measurements. In this presentation, the details of fabrication process and physical properties of Ga2O3 nano chestnut burr will be reported.

• 한국응용과학기술학회지
• /
• 제18권3호
• /
• pp.191-196
• /
• 2001

Organic semiconductors based on vacuum-deposited films of fused-ring polycyclic aromatic hydrocarbon have great potential to be utilized as an active layer for electronic and optoelectronic devices. In this study, pentacene thin films and electrode materials were deposited by Organic Molecular Beam Deposition (OMBD) and vacuum evaporation respectively. For the gate dielectric layer, photoacryl (OPTMER PC403 from JSR Co.) was spin-coated and cured at $220^{\circ}C$. Electrical characteristics of the device were investigated, where the channel length and width was 50 ${\mu}m$ and 5 mm. It was found that field effect mobility was 0.039 $cm^{2}V^{-1}s^{-1}$, threshold voltage was -8 V, and on/off current ratio was $10^{6}$. Further details will be discussed.

• 한국전기전자재료학회논문지
• /
• 제30권4호
• /
• pp.204-209
• /
• 2017

Thermal and structural stability in the glass transition region of chalcogenide glasses has been investigated in terms of thermodynamics for application to various optoelectronic devices. In this study, the compositions of $Ge_xSb_{20}Se_{80-x}$ (x = 10, 15, 20, 25, and 30) were selected to investigate the glass stability according to germanium ratios. The chalcogenide bulks were fabricated by using a traditional melt-quenching method. Thin films were deposited by a thermal evaporation system, maintaining the deposition ratio of $3{\sim}5{\AA}$ in order to have uniformity. The thermal and structural properties were measured by a differential scanning calorimeter (DSC) and X-ray diffraction (XRD). The DSC analysis provided thermal parameters and theoretical glass region stabilities. The XRD analysis supported the theoretical stabilities because of where the crystallization peak data occurred.