Reliable X-Ray diffraction linewidth analysis of metastable cubic GaN thin films using baseline-corrected nonlinear peak fitting

Evaluating the crystalline quality of metastable cubic GaN (c-GaN) thin films requires reliable X-ray diffraction (XRD) linewidth analysis, which can be affected by defect-induced broadening and background contributions. This study systematically compares nonlinear fitting strategies for the c-GaN(200) reflection of films grown on GaP substrates by metal-organic chemical vapor deposition. Unconstrained pseudo-Voigt, fixed-mixing-parameter pseudo-Voigt, baseline-subtracted pseudo-Voigt, and baseline-corrected nonlinear Gaussian fitting were evaluated. Unconstrained pseudo-Voigt fitting artificially overestimated Lorentzian broadening due to background sensitivity, resulting in physically inconsistent linewidths. In contrast, baseline-corrected nonlinear Gaussian fitting provided the most stable and physically consistent full width at half maximum evolution. Using this approach, a systematic linewidth reduction from S1 to S4 was observed, consistent with increased crystallite size and reduced defect density. These results demonstrate the importance of rigorous baseline correction and profile selection for reliable structural analysis of semiconductor thin films.