Micro-Raman characterization of homo-epitaxial n doped GaN layers for vertical device applications

N-doped homo-epitaxial GaN samples grown on freestanding GaN substrates have been investigated by micro-Raman spectroscopy. Quantitative analysis of the E-2(h) and the A(1)(LO) modes' behavior has been performed while intentionally increasing the carrier density using silicon doping. We noticed that as the carrier concentration increases up to 1.8 x 10(18) cm(-3), the E-2(h) mode remains unchanged. On the other hand, when the doping gets higher, the A(1)(LO) position shifts to a higher frequency range, its width becomes larger, and its intensity drastically diminishes. This change in the A(1)(LO) behavior is due to its interaction and its coupling with the free negative charge carriers. Furthermore, we calibrated the A(1)(LO) frequency position shift as a function of the n-carrier concentration. We found out that for low n doping, the change in the A(1)(LO) position can be considered as a linear variation while in the overall doping range, a sigmoid growth trend with a Boltzmann fit can be tentatively applied to describe the A(1)(LO) position shift. This calibration curve can also be used to describe the coupling strength between the carriers and the A(1)(LO) phonon. Eventually, this study shows that micro-Raman spectroscopy is a powerful non-destructive tool to probe the doping concentration and the crystalline quality of GaN material with a microscopic spatial resolution. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/).