Yao-Jun Tsai

Performance of Flip-Chip Thin-Film GaN Light-Emitting Diodes With and Without Patterned Sapphires

We report on improved device performance of flip-chip (FC) GaN-based light-emitting diodes (LEDs) by combining patterned sapphire substrate (PSS) and thin-film techniques. It was found that an FC LED grown on a conventional planar sapphire exhibits a power enhancement factor of only 36.3% after the thin-film processes of substrate removal and surface roughening. In contrast, the as-fabricated FC LED grown on a PSS showed a power enhancement factor of up to 62.3% without any postprocess as compared with the light output power of an original conventional FC LED. Further intensity improvement to 74.4% could be achieved for the FC LED/PSS sample with the thin-film processes.

Novel Electrode Design for Integrated Thin-Film GaN LED Package With Efficiency Improvement

This letter proposes a novel electrode structure for thin-GaN LED applications. The structure enhances light extraction and wall-plug efficiency in thin-GaN LEDs. To enhance light extraction in thin-GaN LEDs and solve current crowding effects caused by electrodes composed of metal, conventional n-GaN electrodes were replaced with ITO conductive films because of their high optical transparency. Simulation results show that the thin-GaN LEDs that use ITO as the nonshielded electrode have a more uniform current density distribution on the n-GaN surface and a higher average internal quantum efficiency than conventional metal electrodes. Furthermore, when a current of 200 mA was applied, the thin-GaN LEDs using the proposed electrode had a 40% increase in light-output power and a significant decrease in chip temperature compared to the use of conventional electrodes. The results indicate that the nonshielded ITO electrode design enhances the light extraction efficiency and avoids the accumulation of heat because of its uniform current density distribution.

A novel integrated structure of thin film GaN LED with ultra-low thermal resistance

This study proposes a novel packaging structure for vertical thin-GaN LED applications by integration of LED chip and silicon-based packaging process. The vertical thin film LED is directly mounted on package submount. The shortest thermal path structure from junction to package submount achieves the lowest thermal resistance of 1.65 K/W for LED package. Experimental results indicate that low thermal resistance significant improved forward current up to 4.6A with 1.125 × 1.125 mm² LED chip size.

Effect of the Flat and Pattern Surface Texturing on Light Extraction of GaN Flip-Chip Light-Emitting Diodes

Device performances of GaN-based flip-chip light-emitting diodes (FC LEDs) with planar and patterned sapphire substrates (PSS) were compared in this study. It was found that for the FC LED with planar sapphire, enhancement factor of luminous intensity can be raised to 107.5% after the processes of substrate removal and surface roughening. By contrast, for the FC LED with PSS, the intensity enhancement factor is already up to 169.5% without any post-processes as compared with the intensity of an as-fabricated conventional FC LED. Further intensity improvement to 205.1% can be achieved for the FC LED with PSS by employing subsequent processes such as substrate removal and surface roughening. These results indicate that the PSS approach is useful in improving light extraction of a nitride-based FC LED.