Study on Laser Lift-Off of GaN HEMTs Grown on Fe-doped and Unintentional Doped Buffer Layer

Separating AlGaN/GaN HEMTs from sapphire substrates is an important segment for transferring GaN onto high thermal conductivity substrate. In this paper, using 248 nm KrF excimer laser lift-off (LLO) system, AlGaN/GaN HEMTs, grown on unintentional doped and Fe-doped buffer layer, were separated from sapphire substrates, respectively. We analyzed the changes of 2DEG characteristic, crystal characteristic and strain state of AlGaN/GaN HEMT before and after LLO by X-ray diffraction (XRD), Hall and Raman. The results indicate the structural quality of HEMT based on unintentional doped GaN buffer layer is slightly affected by LLO process. Instead, for Fe-doped GaN buffer specimen, the 2DEG characteristic has an relatively obvious degeneration after LLO, since film has generated microcracks. XRD, as well as Raman, demonstrated that the residual stress is the mayor inducement for microcracks as a result of Fe-doped GaN with higher compressive stress before LLO.