Lung-Chien Chen

Oblique-Angle Sputtering Effects on Characteristics of Nanocolumnar Structure Anisotropic Indium Tin Oxide Films

We present a nanocolumnar structure anisotropic indium tin oxide (ITO) film deposited at different oblique angles by a radiofrequency magnetron sputtering system. Three dominant diffraction peaks were observed. The location of peaks SnO 2 (110), In 2 O 3 (222), and In 2 O 3 (400) increases from 29.39, 31.34, and 36.34° to 29.45, 31.60, and 36.48°, respectively, as the sputtering oblique angle increases from 0 to 80°. This may be attributed to a high incorporation of oxygen into the film deposited at a high oblique angle. An anisotropic ITO film with a higher oxygen content has a smaller lattice constant, a larger bandgap, a higher resistivity, and a degradation of crystallization. As the flux arrival angle α increases, the absorption edge of the spectra demonstrated a blueshift. The blueshift may result from the Burstein―Moss effect due to the increase in the oxygen content in the anisotropic ITO film or to the quantum confinement effect caused by the exciton quantization in the ITO film.

Effects of spin-polarized injection and photo-ionization of MnZnO film on GaN-based light-emitting diodes

This study discusses the effect of spin-polarized injection and photo-ionization on MnZnO films formed on the surface of GaN-based light-emitting diodes (LEDs). In a magnetic field, the optical output power of GaN-based LEDs increased by about 60% and 50% at injection currents of 20 and 100 mA, respectively. Spin-polarized injection from a MnZnO film and photo-ionization in GaN-based LED can efficiently improve the optical output power of a GaN-based LED. At forward bias of 3.4 V, the forward current of GaN-based LED with MnZnO film in a magnetic field of 0.5 T includes an injection current of 33.71 mA, spin-polarized current of 0.97 mA, and photo-ionized current of 0.4 mA.

Optoelectronic Properties of the p-MnZnO/n-Si Structure Photodiodes in a Strong Magnetic Field

Photodiodes with a p-MnZnO/n-Si substrate structure were fabricated. Mn-doped p-type ZnO (MnZnO) films were deposited by ultrasonic spray pyrolysis on a (100)-oriented silicon substrate. A dark current and a photocurrent of ~4.31×10-7 and 6.95×10-4 A, respectively, were measured at a reverse bias of 2 V, and a photocurrent-to-dark current contrast ratio of almost four orders of magnitude was observed. When a p-MnZnO/n-Si structure photodiode was applied a strong magnetic field of 0.5 T, the photocurrent slightly increases to ~1.24×10-3 A at a reverse bias of 2 V. This may be attributed to the Auger recombination effect due to the applied magnetic field.

Zinc Oxide Doped Indium Oxide Ohmic Contacts to p-Type GaN

We report on the zinc oxide doped indium oxide (ZIO) transparent ohmic contact to the p-GaN. Optimum conditions were selected to minimize the lowest specific contact resistance to 1.4 X 10 -4 Ω cm 2 , as examined by transmission line model after heat treatment process at an alloying temperature of 500°C for 10 min in air. ZIO films were also applied to GaN-based light-emitting diodes (LEDs) to form an electrode with a p-type ohmic contact. A light output power and an external quantum efficiency of the LED with ZIO contact of 5.61 mW and 10.63%, respectively, were measured at a forward current of 20 mA at room temperature.

A nanorods AlN layer prepared by sputtering at oblique-angle and application as a buffer layer in a GaN-based light-emitting diodes

We presents a nanorods AlN films on sapphire substrate deposited at oblique-angle by a radio-frequency reactive magnetron sputtering. A nanorods AlN layer was employed as a buffer layer for a GaN-based LEDs to improve optoelectronic characteristics of LEDs. The diameter of the nanorods AlN buffer layer is in the range of 30-50 nm. Typical current-voltage characteristics of the GaN-based LEDs with a nanorods AlN buffer layer have a forward-bias voltage of 3.1 V at an injection current of 20 mA. The output intensity of LEDs initially increases linearly as the injection current increases from 10 mA to 150 mA. The light output power of the GaN-based LED with a nanoporous AlN layer was about 31% higher than that of a GaN-based LED without a nanoporous AlN layer at an injection current of 250 mA.

Manufacture and photoluminescent properties of molybdate phosphors

In this experiment, the molybdate phosphors were manufactured by using the solid state amorphization with europium, yttrium and molybdenum. To investigate EuxYy(MoO4)3 phosphor characteristics, the europium and yttrium were blended to different of mole ratio. The europium composition can improve phosphors luminous intensity. Phosphors characteristics was measured by X-ray diffraction, SEM and photoluminescence. The X-ray diffraction and SEM displayed phosphors crystal structure. The photoluminescence of molybdate phosphors show that the best excitation spectra emitting position was at 614nm. The molybdate phosphors was excited by UV laser. Therefore, this molybdate phosphors was suitable for UV-LED.

Investigation on optoelectronic characteristics of porous silicon/TiO2/CH3NH3PbI3/graphene heterostructure light-emitting diodes prepared by spin-coating

This work reports the optoelectronic characteristics of the graphene/MAPbI3/TiO2/Si heterostructure and graphene/Pb2/porous Si heterostructure for light-emitting devices with low cost. The XRD diagrams of these two heterostructures show three main peaks at the position of 14.1°, 28.4°, and 31.9°, which correlate with (110), (220), and (310) planes of the MAPbI3 perovskite phase. The PL spectra of these two heterostructures demonstrated three peaks located at 382, 566, and 766 nm. They are corresponding to the emission of B-B transition of TiO2, defects in the TiO2, and B-B transition of MAPbI3. One peak of the EL spectrum of the graphene/MAPbI3/TiO2/porous Si heterostructure operated under the injection current of 10 mA located at around 800 nm was observed.

Characteristics of YAG-doped ZnO/ITO deposited by spraying methed

This work proposes a novel white light device consisted of a yttrium aluminum garnet (YAG) phosphor-doped zinc oxide (ZnO) (ZnO:YAG) thin film deposited on a indium tin oxide (ITO) glass substrate by ultrasonic spray pyrolysis. Characteristics of the ZnO:YAG (YAG at 1, 5, and 10 wt%) film on ITO glass substrates were examined by x-ray diffraction (XRD) pattern, hall measurement, and photoluminescence (PL) pattern spectra. The color of the PL spectra of the yttrium-aluminum garnet (YAG) phosphor-doped zinc oxide (ZnO) thin films under excitation of He-Cd laser with wavelength of 325 nm is nearly white.

GaN-based light-emitting diodes by laser lift-off with electroplated copper

This study presents a GaN thin film light-emitting diode (TF-LED) on an electroplated flexible copper substrate to improve thermal conduction effect of the LED. The optoelectronic characteristics and stress effect of the GaN TF-LEDs on the electroplated flexible copper prepared by laser lift-off technique was examined. The surface of the peeled GaN TF-LED after laser lift-off process demonstrated a pore array. The GaN pore array surface was etched by photo-electrochemical method to form hexagonal pyramid hillocks on the surface using KOH solution. Then, freestanding peeled GaN TF-LEDs with the front surface protected by wax were immersed into 3M KOH solution at 10, 20, 30min under ultraviolet illuminations to perform the photo-electrochemical etching. Surface morphologies with and without photo-electrochemical etching were observed by field emission scanning electron microscope (FESEM) (LEO 1530).

Graphene on Ag films for reflectively conductive layer ohmic contacts to p-type GaN in GaN-based light-emitting diodes

We presents graphene-based reflective electrode on Ag films as a reflectively conductive layer for flip-chip GaN-based LEDs to improve optoelectronic characteristics of LEDs. The Ag/graphene films demonstrate thickness of about 200 nm and surface roughness. As annealing at temperature increases from 500°C to 800°C, the location of peak increases from 22.5° to 26.2° with the peak intensity becomes stronger. This may be attributed to the reduction of oxygen functional group. A graphene has first and second Raman-active modes at D band (1350 cm-1) and G band (1592 cm-1), respectively. Optimal conditions for graphene/Ag films contact of the sheet resistance is the smallest value by after heat treatment at temperatures of 800 °C. Further, graphene/Ag films were also applied to GaN-based light-emitting diodes to form an electrode with a p-type ohmic contact.