A newly developed thin-GaN LED structure has shown great advantages over
traditional LED schemes in the lighting efficiency performance. Yet, in the
fabrication process of thin-GaN LED chip, several processes still remain to be
optimized. In this paper, the process issues of the promising thin-GaN LED chip
will be discussed.
We develop a miniaturized optical signal pickup module, with a working wavelength of 650 nm, and an image numerical aperture (NA) of 0.6, comprised of several SiNX optical phase elements on stacked Si substrates, for use in optical storage systems. The optical module, which is optical-on-axis and transmissible in both visible and infrared ranges, is designed to include not only a light source, but also diffractive optical elements (DOEs), which can be made with micro-optoelectromechanical systems (MOEMS) technology. Its optical operation is simulated by ray tracing to optimize the spot size (~0.6 µm) focused on the disk by adjusting the tolerance of each element in the alignment. All the Si-based transmission optical elements are fabricated and stacked by self-alignment bonding to reduce the tolerance of the assembled system. We obtain a circular focused spot when the full-width at half maximum (FWHM) of the zero-order beam is 3.1 µm; the diffraction limited spot size on the optical disk is 0.7 µm.
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.
In this work, we investigate the optical and electrical properties of inserting a Ni thin barrier between contact layer, NiO-Au, and reflective layer, Al after sequent elevated annealing in air ambient. The reflectivity of NiO-Au/Ni/Al p-GaN contact configurations is 61% in 470nm which is 10% higher than NiO-Au/Al p-GaN contact configurations, after 500°C annealing. By inserting a Ni barrier layer, the specific contact resistance of the NiO-Au/Ni/Al was maintained on the order of 10<sup>-2</sup> Ω-cm<sup>2</sup>, up to an annealing temperature of 500°C. The XPS results confirmed the function of the Ni barrier layer, and it shows relatively low atomic level of Al was detected in the GaN epi-layer. It was found that both the electrical and optical characteristics of NiO-Au/Ni/Al p-GaN contacts exhibited good thermal stability. This high thermal stable P-GaN enables the fabrication of thin-GaN LED device.