Toward efficient light diffraction and intensity variations by using wide bandwidth surface acoustic wave

Lee, Young Ok,Chen, Fu,Lee, Kee Keun Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.6

<P>We have developed acoustic-optic (AO) based display units for implementing a handheld hologram display by modulating light deflection through wide bandwidth surface acoustic wave (SAW). The developed AO device consists of a metal layer, a ZnS waveguide layer, SAW inter digital transducers (IDTs), and a screen for display. When RF power with a particular resonant frequency was applied to IDTs, SAW was radiated and interfered with confined beam propagating along ZnS waveguide layer. The AO interacted beam was deflected laterally toward a certain direction depending on Bragg diffraction condition, exited out of the waveguide layer and then directed to the viewing screen placed at a certain distance from the device to form a single pixel. The deflected angles was adjusted by modulating the center frequency of the SAW IDT (SAW grating), the RF power of SAW, and the angles between propagating light beam path along waveguide and radiating SAW. The diffraction efficiency was also characterized in terms of waveguide thickness, SAW RF input power, and aperture length. Coupling of mode (COM) modeling was fulfilled to find optimal device parameters prior to fabrication. All the parameters affecting the deflection angle and efficiency to form a pixel for a three-dimensional (3D) hologram image were characterized and then discussed. (C) 2016 The Japan Society of Applied Physics</P>

Effect of barrier growth temperature on morphological evolution of green InGaN/GaN multi-quantum well heterostructures

Senthil Kumar, M,Park, J Y,Lee, Y S,Chung, S J,Hong, C-H,Suh, E-K Institute of Physics [etc.] 2007 Journal of Physics. D, Applied Physics Vol.40 No.17

<P>Surface morphology of green InGaN/GaN multi-quantum wells (MQWs) on a sapphire substrate with various high temperature grown GaN barriers has been evaluated. Keeping the InGaN well growth temperature constant at 740 °C, a series of MQWs were grown with GaN barrier temperatures varied up to 910 °C. GaN barriers grown below 800 °C lead to the generation of a high density of V-defects and inclusions embedded within V-defects as observed by atomic force microscopy. Scanning electron microscopy and cathodoluminescence (CL) studies revealed that the embedded inclusions are of two kinds: one of them appears as bright spots in CL mapping while the other appears as the surrounding region. Temperature ramping and subsequent interruption for GaN barrier growth suppresses both kinds of inclusion defects and also significantly reduces the V-defect density. An inclusion-free smooth surface is obtained for green emitting InGaN/GaN MQWs with the GaN barrier grown at 910 °C.</P>

Improvement in negative bias illumination stress stability of In–Ga–Zn–O thin film transistors using HfO₂ gate insulators by controlling atomic-layer-deposition conditions

Na, So-Yeong,Kim, Yeo-Myeong,Yoon, Da-Jeong,Yoon, Sung-Min Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.49

<P>The effects of atomic layer deposition (ALD) conditions for the HfO<SUB>2</SUB> gate insulators (GI) on the device characteristics of the InGaZnO (IGZO) thin film transistors (TFTs) were investigated when the ALD temperature and Hf precursor purge time were varied to 200, 225, and 250 °C, and 15 and 30 s, respectively. The HfO<SUB>2</SUB> thin films showed low leakage current density of 10<SUP>−8</SUP> A cm<SUP>−2</SUP>, high dielectric constant of over 20, and smooth surface roughness at all ALD conditions. The IGZO TFTs using the HfO<SUB>2</SUB> GIs showed good device characteristics such as a saturation mobility as high as 11 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, a subthreshold swing as low as 0.10 V/dec, and all the devices could be operated at a gate voltage as low as  ±3 V. While there were no marked differences in transfer characteristics and PBS stabilities among the fabricated devices, the NBIS instabilities could be improved by increasing the ALD temperature for the formation of HfO<SUB>2</SUB> GIs by reducing the oxygen vacancies within the IGZO channel.</P>

Modulation of electrical mobility in Au ion irradiated titanium oxide with crystal field splitting

Park, Hyun-Woo,Jun, Byung-Hyuk,Choi, Dukhyun,Chung, Kwun-Bum Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.11

<P>Electrical modulation of radio frequency (RF) sputtered TiO2-x films were investigated as a function of Au swift heavy ion irradiation dose at room temperature. The prepared TiO2-x films were irradiated with 130MeV Au swift heavy ion in the range from 1x 10(11) to 5 x 10(12) ions/cm(2). As the Au ion irradiation dose increased up to 1 x 10(12) ions/cm(2), the electrical mobility of TiO2-x films were dramatically increased 3.07 x 10(2) cm(2)V(-1) s(-1) without the change of carrier concentration. These changes in electrical properties of Au irradiated TiO2-x film, are related to the modification of electronic structure such as crystal field splitting of Ti 3d orbital hybridization and sub-band edge states below the conduction band as a function of Au swift heavy ion irradiation dose. (C) 2016 The Japan Society of Applied Physics</P>

50 kHz bottom backscattering measurements from two types of artificially roughened sandy bottoms

Son, Su-Uk,Cho, Sungho,Choi, Jee Woong Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.7

<P>Laboratory measurements of 50 kHz bottom backscattering strengths as a function of grazing angle were performed on the sandy bottom of a water tank; two types of bottom roughnesses, a relatively smooth interface and a rough interface, were created on the bottom surface. The roughness profiles of the two interface types were measured directly using an ultrasound arrival time difference of 5MHz and then were Fourier transformed to obtain the roughness power spectra. The measured backscattering strengths increased from -29 to 0 dB with increasing grazing angle from 35 to 86 degrees, which were compared to theoretical backscattering model predictions. The comparison results implied that bottom roughness is a key factor in accurately predicting bottom scattering for a sandy bottom. (C) 2016 The Japan Society of Applied Physics</P>

Effect of cyclic outer and inner bending on the fatigue behavior of a multi-layer metal film on a polymer substrate

Kim, Byoung-Joon,Shin, Hae-A-Seul,Lee, Ji-Hoon,Joo, Young-Chang Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.6

<P>The electrical reliability of a multi-layer metal film on a polymer substrate during cyclic inner bending and outer bending is investigated using a bending fatigue system. The electrical resistance of a Cu film on a polymer substrate during cyclic outer bending increases due to fatigue damage formation, such as cracks and extrusion. Cyclic inner bending also leads to fatigue damage and a similar increase in the electrical resistance. In a sample having a NiCr under-layer, however, the electrical resistance increases significantly during outer bending but not during inner bending mode. Cross-sectional observations reveal that brittle cracking in the hard under-layer results in different fatigue behaviors according to the stress mode. By applying an Al over-layer, the fatigue resistance is improved during both outer bending and inner bending by suppressing fatigue damage formation. The effects of the position, materials, and thickness of the inter-layer on the electrical reliability of a multi-layer sample are also investigated. This study can provide meaningful information for designing a multi-layer structure under various mechanical deformations including tensile and compressive stress. (C) 2016 The Japan Society of Applied Physics</P>

Thermometry of combustion gases using light emission and acoustic wave from laser-induced sparks

Lee, Jungwun,Bong, Cheolwoo,Sun, Hojoong,Jeong, Jinkyu,Bak, Moon Soo Institute of Physics Publishing Ltd. 2019 Journal of Physics. D, Applied Physics Vol.52 No.31

<P>A new method to measure local combustion gas temperatures is proposed using light emission and acoustic wave from laser-induced sparks. Because the speed of sound is a function of temperature as well as species composition, the time-of-arrival measurements of the acoustic waves from each of the two laser-induced sparks separated by a certain distance were carried out using a high-frequency response microphone. As the microphone was installed in the same plane and line as the two laser sparks, the acoustic wave from the laser spark farther from the microphone traveled through the same region as the acoustic wave from the laser spark nearer to the microphone, and thus, the speed of sound for the region between the sparks can be estimated from the difference in the arrival times. Optical emission spectroscopy was also carried out on one of the laser sparks to estimate the species composition, and the linear relationship between the intensity ratio of atomic hydrogen to oxygen and fuel–air equivalence ratio was confirmed. Assuming that the gas reached its equilibrium state, the temperatures were obtained from the measured speed of sound and found to be systematically higher than the adiabatic flame temperatures by approximately 77 K. The repeatability of the measurement was within  ±38 K. The proposed method is appropriate for applications in which the temperature is high and contact measurements are difficult.</P>

Light-induced changes in silicon nanocrystal based solar cells: Modification of silicon-hydrogen bonding on silicon nanocrystal surface under illumination

Kim, Ka-Hyun,Johnson, Erik V.,Roca i Cabarrocas, Pere Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.7

<P>Hydrogenated polymorphous silicon (pm-Si:H) is a material consisting of a small volume fraction of nanocrystals embedded in an amorphous matrix. pm-Si:H solar cells demonstrate interesting initial degradation behaviors such as rapid initial change in photovoltaic parameters and self-healing after degradation during light-soaking. The precise dynamics of the light-induced degradation was studied in a series of light-soaking experiments under various illumination conditions such as AM1.5G and filtered 570 nm yellow light. Hydrogen effusion experiment before and after light-soaking further revealed that the initial degradation of pm-Si:H solar cells originate from the modification of silicon-hydrogen bonding on the surface of silicon nanocrystals in pm-Si:H. (C) 2016 The Japan Society of Applied Physics.</P>

Analysis of a modified recessed active tunneling field-effect transistor

Kim, HuiJung,Choi, Seongwook,Yoo, NakWon,Rhee, SeungMan,Lee, Myoung Jin,Park, Young June Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.7

<P>To enhance the on-current (I-ON) of a tunneling field-effect transistor (TFET), we investigated the structures of a TFET with a recessed active (RA) region, known as the 'RA-TFET', using three-dimensional (3D) simulation. The analyzed structure is different from the recessed dynamic random-access memory (DRAM) channel in terms of the positions of the source and drain. The benefit of this structure is that the tunneling length remains unchanged as the depth increases so that the current can be easily scaled up, thereby maintaining the subthreshold slope (SS) and active area. Using an RA-TFET with a 100 nm Si depth, a 9.45 x 10(-7) A I-ON is achieved with a minimum SS of 35 mV/dec; in addition, we propose RA-TFET modifications to mitigate the ambipolar characteristics and reduce the capacitance between the gate and the drain (C-GD) by up to 40%. (C) 2016 The Japan Society of Applied Physics</P>

Oxygen and nitrogen plasma etching of three-dimensional hydroxyapatite/chitosan scaffolds fabricated by additive manufacturing

Myung, Sung-Woon,Kim, Byung-Hoon Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.1

<P>Three-dimensional (3D) chitosan and hydroxyapatite (HAp)/chitosan (CH) scaffolds were fabricated by additive manufacturing, then their surfaces were etched with oxygen (O-2) and nitrogen (N-2) plasma. O-2 and N-2 plasma etching was performed to increase surface properties such as hydrophilicity, roughness, and surface chemistry on the scaffolds. After etching, hydroxyapatite was exposed on the surface of 3D HAp/CH scaffolds. The surface morphology and chemical properties were characterized by contact angle measurement, scanning electron microscopy, X-ray diffraction, and attenuated total reflection Fourier infrared spectroscopy. The cell viability of 3D chitosan scaffolds was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The differentiation of preosteoblast cells was evaluated by alkaline phosphatase assay. The cell viability was improved by O-2 and N-2 plasma etching of 3D chitosan scaffolds. The present fabrication process for 3D scaffolds might be applied to a potential tool for preparing biocompatible scaffolds. (C) 2016 The Japan Society of Applied Physics</P>