We report the fabrication of mechanical lift-off high quality thin GaN with Hexagonal Inversed
Pyramid (HIP) structures for vertical light emitting diodes (V-LEDs). The HIP structures were
formed at the GaN/sapphire substrate interface under high temperature during KOH wet etching
process. The average threading dislocation density (TDD) was estimated by transmission electron
microscopy (TEM) and found the reduction from 2×109 to 1×108 cm-2. Raman spectroscopy analysis
revealed that the compressive stress of GaN epilayer was effectively relieved in the thin-GaN
LED with HIP structures. Finally, the mechanical lift-off process is claimed to be successful by using
the HIP structures as a sacrificial layer during wafer bonding process.
We demonstrate high efficiency blue light emitting diodes with defect passivation layers. The defect passivation layers
were formed by defect selective wet etching, SiO2 deposition, and chemical mechanical polishing process. The process
does not require photolithography patterning. The threading dislocation density of grown sample was reduced down to
~4×107 cm-2. The defect passivated epi-wafer is used to grow light emitting diode (LED) and the output power of the
fabricated chip is enhanced by 45% at 20 mA compared to a reference one without using defect passivation.
Three years (2003-2005) of aerosol optical depths (AOD) measured with CIMEL sunphotometer were compared to the surface concentrations of PM10 and PM2.5 in Northern (i.e. Taipei) and Southern (i.e. Tainan) Taiwan. The correlation between AOD and PM10 is higher in Taipei than in Tainan. Additional chemical compositions of PM10 and PM2.5 in these two sites, including ionic component, sea salt, OC/EC and crustal components, were also examined to find their relationship with the AOD. These analyses indicate that aerosols in Taipei are mainly composed of fine aerosols, whereas in Tainan more crustal material and OC exist in the coarse mode, which partially explain the higher correlation of PM10 and AOD in Taipei. Closure calculations are carried out by combining data from lidar, sunphotometer, nephelometer, aethalomter, SMPS and APS size spectrometers, as well as chemical analyses of aerosols from PM10 and PM2.5 samplers and MOUDI impactor to investigate their consistency. The observed surface single scattering albedo was also compared to that retrieved by CIMEL sunphotometer, with additional discussion on the possible explanation to the discrepancies of the comparisons. Then, lidar measurement is applied to relate aerosols at the surface to those aloft.
Nowadays, the high power GaN-based LED has attracted serious attention for the lighting application. One of key issues for high power GaN-base LED to achieve sufficient lighting efficiency over the traditional light sources, such as, white incandescent and halogen light bulb is the efficiency of heat dissipation. Typically, GaN epi-layer is grown on sapphire substrates. The poor thermal conductivity of sapphire substrate has been identified to be the main limitation for the application of high power GaN LED. To improve the heat dissipation and lighting efficiency, we report a thin GaN structure by using Au-Si wafer bonding and Laser lift-off (LLO) technique. The GaN wafer was first deposited with a Au bonding layer and bonded onto a good thermal conduction substrate, i.e., heavy-doped Si. Then, 248nm KrF excimer Laser was used to strip the original sapphire substrate. To assure a successful GaN epi-layer transferring, Raman spectrum on the transferred GaN layer was performed and the result shows no quality change in the transferred GaN layer. In this work, we also fabricated the vertical LED devices on the transferred GaN epi-layer. Therefore, L-I-V result was obtained which will be presented in this talk. Moreover, we will discuss the effects and advantages of Au-Si bonding on the efficiency of lighting.