Chun-Hung Wu

A reflective polarizer-free electro-optical switch using dye-doped polymer-stabilized blue phase liquid crystals

We demonstrate a reflective polarizer-free electro-optical switch using dye-doped polymer-stabilized blue phase liquid crystals (DDPSBP-LC). At the voltage-off state, the dye molecules and liquid crystals form the structure of the double twist cylinders. As a result, the DDPSBP-LC is in dark state due to the combination of Bragg reflection and light absorption. At the voltage-on state, the blue phase structure is unwound locally. The DDPSBP-LC is then in bright state because of the small light absorption only. The applications of such a switch are shutter glass of 3D displays, and electronic papers.

Hysteresis-free polymer-stabilized blue phase liquid crystals using thermal recycles

We demonstrate a hysteresis-free polymer-stabilized blue phase liquid crystals (PSBP-LCs) using thermal recycles by means of enlarging the domain size of PSBP-LC and improving the uniformity of the crystal orientations of PSBP-LC. The crystal growth of PSBP-LCs bases on a competition between the heterogeneous nucleation and the homogeneous nucleation is also demonstrated and discussed. This study opens a new window for understanding the hysteresis of the PSBP-LC and assisting in designing many PSBP-LC-based photonic devices, such as displays, electro-optical switches, and electrically tunable focusing LC lenses.

Measuring electric-field-induced birefringence in polymer stabilized blue-phase liquid crystals based on phase shift measurements

A simple optical method to measure the electric-field-induced birefringence and Kerr constant of polymer-stabilized blue-phase liquid crystals (PSBP-LC) is demonstrated. By measuring the phase shift of PSBP-LC and the averaged refractive index of PSBP-LC at the voltage-off state, the ordinary refractive index and extraordinary refractive index of PSBP-LC as function of applied voltage can be obtained experimentally. As a result, the electric-field-induced birefringence and Kerr constant can be determined as well. The method we proposed can help in designing PSBP-LC–based photonic devices.

LOW-TEMPERATURE LUMINESCENT PROPERTIES OF DEGENERATE P-TYPE GAAS GROWN BY LOW-PRESSURE METALORGANIC CHEMICAL-VAPOR-DEPOSITION

Low‐temperature (20 K) luminescent properties of heavily carbon‐ and zinc‐doped GaAs grown by low‐pressure metalorganic chemical vapor deposition were investigated. The luminescence linewidth became broader at low temperatures when p≳4×1019 cm−3 due to the appearance of a shoulder peak. The main peak shifted to low energy when the dopant concentration was increased; however, the shoulder peak was at around 1.485 eV and was nearly independent of the dopant concentration. The peak of the band‐to‐acceptor transition occurred at low temperature and dominated the emission spectra of degenerate GaAs. The peak energy of Zn‐doped samples was lower than that of C‐doped samples because of the existence of defects. The excitation power intensity was varied to investigate the behavior of the shoulder peak for both types of dopants. The shoulder peak was a part of the main peak because of the recombination between the conduction band and the bottom of the impurity band.

In0.49Ga0.51P/GaAs heterostructures grown by low-pressure metalorganic chemical vapor deposition

We have successfully grown In0.49Ga0.51P/GaAs heterostructures and made InGaP‐based high electron mobility transistors (HEMTs) by low‐pressure metalorganic chemical vapor deposition. We have found the epitaxial layer of InGaP with a Hall mobility of 4073 cm2/Vu2009s (300 K) and the photoluminescence full width at half‐maximum of 1 meV (4.2 K) for GaAs, 12 meV (4.2 K) for In0.49Ga0.51P. Zinc‐induced disordering phenomenon was examined by transmission electron microscope. By Shubnikov‐de Haas measurement, we demonstrated the existence of a two‐dimensional electron gas in InGaP/GaAs heterojunctions. The sheet carrier concentration of 2DEG is around 8.8×1011 cm−2 at 1.5 K. A HEMT device with 1 μm×40 μm gate (pattern) shows an extrinsic transconductance of 65.5 mS/mm and an intrinsic transconductance of 266 mS/mm at 300 K.

Anomalous mobility enhancement in heavily carbon‐doped GaAs

An anomalous mobility enhancement and metallic‐type conductivity were observed in heavily carbon‐doped GaAs grown by low‐pressure metalorganic chemical vapor deposition. The 77 K mobility was slightly lower than that of 300 K for hole concentration between 1×1018 and 4×1018 cm−3. However, the 77 K mobility was enhanced from p≳4×1018 cm−3, and the 300 K mobility slowly decreased with increasing hole concentration that ranged from 7×1018 to 3×1019 cm−3. As a result, the 77 K mobility was around 50%–60% greater than the 300 K mobility due to the metallic‐type conductivity.

Doping of InGaP epitaxial layers grown by low pressure metal-organic chemical vapor deposition

Abstract DEZn and H 2 Se were utilized as p- and n-type dopant sources for the growth in InGaP layers by low pressure metal-organic chemical vapor deposition (LP-MOCVD). The decrease in intensity of the extra spots of electron diffraction indicates that disordering is induced by the zinc doping. Streaky and wavy diffraction patterns demonstrate the formation of anti-phase domains caused by the Se dopant incorporation. The growth rate of the grown layer is reduced by more than 10% owing to the dopant incorporation. A photoluminescence emission energy difference of 141 meV between undoped and Zn-doped (5.8 × 10 18 cm −3 ) InGaP was obtained. The effects of doping on disordering, degeneracy of quasi-Fermi level and lattice constant reduction of grown layers were included in this study.

Hysteresis of Polymer Stabilized Blue Phase Liquid Crystals

We demonstrate a hysteresis-free polymer-stabilized blue phase liquid crystals (PSBP-LCs) as well as hysteresis-free dye-doped polymer stabilized blue phase liquid crystals (DDPSBP-LCs) by means of enlarging the domain size and improving the uniformity of the crystal orientations of PSBP-LC and DDPSBP-LC. The mechanism based on the crystal growth is proposed. The hysteresis-free PSBP-LC (or DDPSBP-LC) is important in PSBP-LC-based photonic devices, such as displays, electro-optical switches, and electrically tunable focusing LC lenses.

P‐149: A Reflective Polarizer‐Free Display Using Dye‐Doped Polymer‐Stabilized Blue Phase Liquid Crystals

We demonstrate a reflective polarizer-free display using dye-doped polymer-stabilized blue phase liquid crystals (DDPSBP-LC). The mechanism is mainly the combination of electrically tunable light absorption and Bragg reflection. At the voltage-off state, the dye molecules and liquid crystals form the structure of the double twist cylinders. As a result, the DDPSBP-LC is in dark state due to the combination of Bragg reflection and light absorption. At the voltage-on state, the blue phase structure is unwound locally. The DDPSBP-LC is then in bright state because of the small light absorption only. The response time of DDPSBP-LC is fast, the viewing angle is wide, and the optical efficiency is high. The applications of such a switch are shutter glass of 3D displays, and electronic papers.

Semi-insulating iron-doped indium phosphide grown by low-pressure metal-organic chemical vapour deposition

Abstract(C5H5)2Fe and Fe(CO)5 were used as the 3d transition-metal dopant sources in the growth of semi-insulating InP epitaxial layers by low-pressure metal-organic chemical vapour deposition (MOCVD). From the bright- and dark-field images of transmission electron microscopy (TEM) analysis, many precipitates were observed. Three extra peaks in the X-ray diffraction pattern were found. The peaks of band-band recombination, donor-acceptor pair recombination transitions and the recombination of donor-acceptor pair with one-phonon emission were observed in the short-wavelength range of low-temperature photoluminescence measurement. Three Fe-related peaks were observed at 0.7079, 0.6897 and 0.6683 Ev. For a wide range (10–600) of In/Fe molar fraction, the resistivity remained at high values (about 108 Ω cm) and the highest resistivity appeared at 5 × 108 Ω cm for a 1 Μm layer with a breakdown voltage of 9 V.