Effect of the Buffer Layers on the Strain Distribution in GaN‐Based Power Transistors using Surface‐Enhanced Raman Spectroscopy

Ex situ room‐temperature strain profiling is analyzed by selectively obtaining surface‐specific Raman spectra as a function of the distance from the surface in GaN‐based power electronic devices. With obliquely truncated structures and by optimizing the surface plasmon resonance of Ag nanoparticles attached to the surface, it becomes possible to observe the development of the strain relaxation process through the epilayer thickness. The initial GaN strain varies depending on the thickness of the AlN buffer. When the thickness of AlN buffer layer is relatively thick, initial strong compressive strain is generated in the GaN epilayers. In contrast, when AlN thickness is thin, then initial strain in GaN is tensile, and the strain reversal is measured after certain thickness. This strain reversal is attributed to the insertion of thin AlGaN interlayers, which can generate compressive strain in the GaN grown on a Si substrate and played a crucial role in altering the overall strain evolution.