Buckling on Fe‐Doped AlGaN/GaN High Electron Mobility Transistor Films after Laser Liftoff Process: Phenomena and Mechanism

다국어 초록 (Multilingual Abstract)

The influence of Fe in the buffer layer on the laser liftoff (LLO) of GaN high electron mobility transistors is presented herein. LLO is performed on Fe‐doped GaN films using a KrF excimer LLO system. The morphology, crystal characteristics, and 2D electron gas (2DEG) characteristics of the GaN films after LLO are characterized using a 3D optical microscope, X‐ray diffraction, and Hall methods. The present work is different from previous methods because of the large‐area buckling instead of cracks on the Fe‐doped GaN films. The results show that the crystal quality and 2DEG characteristics of the buckled parts are significantly affected. Furthermore, a modified simulation model of the temperature and thermal‐induced stress fields in the films is used to explain the buckling of the films, whose results are consistent with the characterization results. The additional absorption centers induced by the Fe impurity energy levels increase the gradient of temperature field, thereby increasing the compressive stresses in the films at the edges of the laser spots. Moreover, a higher temperature is observed at the interface between the film and the bonding glue, which results in the debonding. Therefore, Fe‐doped GaN films are more prone to buckling than unintentionally doped GaN films.
Herein, it is reported that a large‐area buckling occurs when the Fe‐doped GaN high electron mobility transistor (HEMT) film is separated from the sapphire substrate by a laser liftoff process. A simulation model of the temperature and thermal‐induced stress fields in the films combined with the model of film buckling is used to explain the buckling mechanism.