I have grown germanium film on glass coated with copper. deposited films were annealed at various temperatures. the FWHM decreases (indicating Crystal size increses) while intensity also decreases.
As of my knowledge Ge has multiple phases. Also, here you observed the decrease in intensity of the peaks. So this could be useful to see the XRD pattern with variation of temperature. This paper would be useful to answer this question. https://doi.org/10.1063/5.0047359