Interfacial stress characterization of GaN epitaxial layer with sapphire substrate by confocal Raman spectroscopy

As an important wide-bandgap semiconductor, gallium nitride (GaN) has attracted considerable attention. This paper describes the use of confocal Raman spectroscopy to characterize undoped GaN, n-type GaN, and p-type GaN through depth profiling using 405-, 532-, and 638-nm wavelength lasers. The Raman signal intensity of the sapphire substrate at different focal depths is studied to analyze the depth resolution. Based on the shift of the E2H mode of the GaN epitaxial layer, the interfacial stress for different types of GaN is characterized and calculated. The results show that the maximum interfacial stress appears approximately at the junction of the GaN and the sapphire substrate. Local interfacial stress analysis between the GaN epitaxial layer and the substrate will be very helpful in furthering the applications of GaN devices.