Fabrication of gan light emitting diodes by laser lift-off technique

The GaN-based wide band gap semiconductors have been employed for blue light emitting diodes (LEDs) and laser diodes. These devices were grown heteroepitaxially onto dissimilar substrates such as sapphire and SiC because of difficulties in the growth of bulk GaN. However, due to the poor electrical and thermal conductivity of sapphire substrate, the device process steps are relatively complicated compared with other compound semiconductor optoelectronic devices. Therefore, fabrication of GaN-based light emitting devices on electrically and thermally conducting substrate by separating sapphire substrate is most desirable. Several techniques were used to achieve this process including, metallization and wafer bonding, lift-off, and layer transfer. In this thesis, we report the research results on the fabrication of free standing GaN LEDs on conductivity substrate. In this chapter, the establishment of laser lift-off (LLO) conditions for freestanding GaN thin film was presented. By combing the LLO process, new p-type ohmic contact metallization, and wafer bonding techniques, the performance of freestanding LLO-LEDs on copper substrate with p-side up and p-side down configuration, and a large-area-emission LEDs were demonstrated.