M. Y. Kuo

The Influence of the Thermal Effect on CdSe/ZnS Quantum Dots in Light-Emitting Diodes

This study investigates the effect of temperature on CdSe/ZnS quantum dots (QDs) in GaN-based light-emitting diodes (LEDs) using the phosphor conversion efficiency (PCE) and LED junction temperature. In our simulation, the blue chip and CdSe/ZnS QDs temperature are similar because of their minimal thickness. Furthermore, to verify the effect of temperature on CdSe/ZnS QDs, we use continuous wave and pulsed current sources to measure the relationship between the temperature and relative PCE. Higher junction temperatures are observed with greater CdSe/ZnS QD volume in LEDs. This is attributed to the thermal conduction and nonradiative energy between CdSe/ZnS QDs and blue chip. Therefore, if thermal management is improved, CdSe/ZnS QDs are expected to be used as color converting material in LEDs.

Quantum efficiency enhancement in selectively transparent silicon thin film solar cells by distributed Bragg reflectors.

This work demonstrated a-Si:H thin-film solar cells with backside TiO(2)/ SiO(2) distributed Bragg reflectors (DBRs) for applications involving building-integrated photovoltaics (BIPVs). Selectively transparent solar cells are formed by adjusting the positions of the DBR stop bands to allow the transmission of certain parts of light through the solar cells. Measurement and simulation results indicate that the transmission of blue light (430 ~500 nm) with the combination of three DBR mirrors has the highest increase in conversion efficiency.

Lasing in metal-coated GaN nanostripe at room temperature

We demonstrated lasing in a metal-coated GaN nano-stripe under room temperature pulsed operation, and the lasing mode at 370nm were observed. Aluminum and SiO2 layers were coated on the undoped GaN nano-stripe.

Room temperature lasing with high group index in metal-coated GaN nanoring

The room temperature lasing action from a metal-coated GaN nanoring cavity was observed by optical pumping. The GaN nanoring is 7 μm in diameter and 400 nm in width. The quality factor of the cavity is approximately 860 with a threshold power density of 37.5 mJ/cm2. Such a device performance was attributed to the combination of metal-coated nanocavity with whispering-gallery modes. Moreover, the group index extracted from the experiment was 5.99 and was verified with calculations and analyses of the lasing modes as well as their characteristics. The study showed a promising way to further improve the performance of metal-coated nanolasers.

Effect of the Thermal Characteristics of Phosphor for the Conformal and Remote Structures in White Light-Emitting Diodes

The influence of the thermal effect of phosphor for conformal and remote structures in white light-emitting diodes was investigated using the junction and phosphor temperatures. Comparing the measured temperatures with IR thermometer, the remote structure has a higher phosphor temperature than the conformal structure. This result indicates that the phosphor in the conformal structure has demonstrated superior conduction because of the high thermal conductivity in surrounding. Furthermore, thermal distribution in the simulation results has shown to have favorable agreement with the experimental results. Consequently, the lifetime measurement is shown to verify the results of the simulation and experiment for both structural types.

Large-area ultraviolet GaN-based photonic quasicrystal laser with high-efficiency green color emission of semipolar {10-11} In0.3Ga0.7N/GaN multiple quantum wells

In this study, a multi-color emission was observed from the large-area GaN-based photonic quasicrystal (PQC) nanopillar laser. The GaN PQC nanostructure was fabricated on an n-GaN layer by using nanoimprint lithographic technology. The regrown InGaN/GaN multiple quantum wells (MQWs) formed a nanopyramid structure on top of the PQC nanopillars. A lasing action was observed at ultraviolet wavelengths with a low threshold power density of 24 mJ/cm2, and a green color emission from InGaN/GaN MQWs was also achieved simultaneously.

Large Area of Ultraviolet GaN-Based Photonic Quasicrystal Laser

In this study, large-area GaN-based photonic quasicrystal (PQC) nanopillars were fabricated on an n-GaN substrate using the nanoimprint lithography (NIL) technique. Under optical pumping condition, a high lasing action from the GaN photonic quasicrystals was observed. The lasing wavelength is at 366 nm with a low threshold power density of 0.009 kW/cm2. To confirm the band-edge lasing mode, the finite-element method (FEM) was used to perform the simulation for the 12-fold symmetry photonic quasicrystal lattices.

Enhancement of the Purcell effect for colloidal CdSe/ZnS quantum dots coupled to silver nanowires by a metallic tip

In this study, the Purcell effect for CdSe/ZnS quantum dots emission coupled to a silver nanowire cavity was investigated. We manipulated the interaction between colloidal quantum dots (QDs) and an Ag NW in the presence of a metallic tip. When a metal tip approaches the Ag NW, the Ag surface plasmon mode could be lifted away from the metallic NW so that a low optical loss could still be obtained. This work demonstrates enhancement of the spatial coupling between the plasmonic mode and light sources and reduction in metal Ohmic losses, resulting in an enhanced Purcell effect and coupling efficiency accompanied with increased fluorescence intensity.

Investigation of the thermal characteristics with the conformal and remote phosphor structures in white light-emitting diodes

1 Department of Photonics and Institute of Electro-Optical Engineering, National Chiao-Tung University, Hsinchu, Taiwan 2 Research Center for Applied Sciences, Academia Sinica 128 Academia Rd., Sec. 2 Nankang, Taipei 115 Taiwan 3 Institute of Photonic Systems, College of Photonics, National Chiao-Tung University,Tainan ,Taiwan 71150 4 HELIO Optoelectronics Corp., Taiwan E-mail: mhshih@gate.sinica.edu.tw

Wavelength fine-tuning flexible photonic crystal rods laser

In this study, a flexible photonic crystal laser was demonstrated with InGaAsP nano rods on a polydimethylsiloxane (PDMS) substrate. The InGaAsP nano-rods content 4 quantum wells which are designed for 1.55 μm communication wavelength. The lasing action was observed around 1550nm which is a band-edge emission at high-symmetry Γ-point of photonic crystals. One of advantages of the flexible laser is the fine-tuning of optical properties by manipulating its geometry. In this work, we observed the lasing wavelength can be controlled by increasing photonic crystal lattice extension. The lasing wavelength was linearly red-shift up to 6 nm as the lattice extension percentage increased to 2.2%. The wavelength tuning rate is approximately 2.69 nm for 1 % lattice extension. Those geometric fine-tuning properties indicate the flexible photonic crystal laser can be applied as a compact tunable light source in photonic crystal integrated circuits or biomedical sensors.