Thermal Stability and Degradation Analysis of GaN/AlGaN Heterostructure
- Author(s): Zhang, Teng
- Advisor(s): Streit, Dwight C
- et al.
AlGaN/GaN heterostructure is one of the most important materials in applications like High Electron Mobility Transistors (HEMT) and other high speed high power devices. Harsh environment is often encountered for these devices so the thermal stability of the AlGaN/GaN heterostructure is essential. Despite large efforts spent in the last decades, the reliability of GaN HEMT and GaN related devices still represent an issue. The role of high temperature in the degradation of AlGaN/GaN heterostructure is controversial and multiple process occur simultaneously upon thermal activation.
This work presents a study of thermal stability of AlGaN/GaN heterostructure in various temperature and different atmosphere. X-ray diffraction and Raman spectroscopy were utilized to characterize the structure degradation. For N2 atmosphere annealing, crystal structure can be maintained up to 1000C, with better crystallinity due to recrystallization. The FWHM drop for N2 annealed sample is up to 38.9%. Significant degradation is observed when annealed in air: (i) irreversible lattice relaxation; (ii) oxidation and defect propagation; (iii) phase separation of AlGaN. Starting from 750C, no crystal structure of AlGaN can be detected. Possible failure mechanism is discussed, and these results may be instructive for future device fabrication and optimization.