Optoelectronic Properties of Phosphor Free Quantum Dot White Light Flip-Chip Leds (Ii)

In 1993, Nichia Corporation discovered a production compatible way to make the first white LED which combines a blue light-emitting diode (LED) die and a gadolinium YAG phosphor, which could convert blue light to yellow. Owing to its longer life time, robust, small size, energy efficiency, and lower operational voltage, make it perfectly to be the mainstream in the field of lighting in this century. Currently, the study of white light LED focuses on the lighting efficiency enhancement, improvement of color rendering index (CRI), thermal stability of phosphor…, and the research of phosphor-free white LED (WLED) is also included. During epitaxial growth, the strain comes from the lattice mismatch. Then the correspondent strain energy release induces the generation of defect and the phase separation in the lattice interfaces. For example, in the InN/GaN structure, growth film instability and spinodal decomposition thus no-uniform distribution of indium-rich aggregates with designed single and concentration formatted in this work behaved as self-assembled quantum dots (QDs), which can construct the phosphor-free white InGaN/GaN LED. The objective of this work is to study and fabricate a phosphor-free white light flip-chip (FC) LED consisting of multilayers of quantum wells and quantum dots (QW-QDs) structures. The emitting white light is mixed by the blue light from quantum wells and the orange light from quantum dots. In the summer of 2016, we had designed and then fabricated the QW-QDs WLED die by metal organic chemical vapour deposition system (MOCVD) and other related semiconductor process equipment. The important issue is to prevent the uneven distribution of quantum dots and the interactive electronic transition between QDs and QW layers (inter transition). In the year of 2017, the major goals and approaches designed to accomplish the WLED die and solve the problem about bad EL results associated with overheating issues. The chip WLED and the sub-mount are FC bounded to produce a power flip-chip QW-QDs WLED with high thermal conductivity AlN submount, using thermo-sonic bonding technology. After the whole WLED fabrication processes are accomplished, the correspond IV, PL and EL measurements are adopted to analyze their optical and electrical characteristics. Finally we will discuss how to optimize its color rendering index and lighting efficiency.

Project ID:PB10608-3648
External Project ID:MOST106-2221-E182-060