The Halide Vapor Phase Epitaxy (HVPE) Method is at the moment the most popular technique for the development of bulk GaN substrates. This process is still in a rather early stage, but the material produced is of interest for studies of the HVPE process as well as the physical properties of bulk GaN. The HVPE growth of GaN in different laboratories is so far essentially done on homemade growth equipment, meaning that growth conditions in different laboratories cannot be directly compared. We shall give some materials characteristics related to the growth conditions in our growth systems, related to structural defects but mainly optical properties. The residual impurities and their corresponding optical signatures will be discussed. In particular residual acceptors are of interest.