Gallium nitride (GaN) crystals doped with erbium, were grown via the ammonothermal processes on hydride vapor phase epitaxy (HVPE) GaN seeds. The crystallization conducted in alkaline solutions of supercritical ammonia and potassium azide (KN3) at temperatures between 525 and 550 degrees C yielded growth rates of 15 and 50 pin day on the gallium and nitrogen polar faces, respectively. X-ray diffraction studies indicated single-crystalline growth on the N-polar surface while the Ga-polar surfaces resulted in polycrystalline growth. Photoluminescence spectra acquired at 15 K showed optical transitions corresponding to the inner shell transitions of erbium centers as well as a strong band edge and blue luminescence peaks centered at 3.495 and 2.90 eV, respectively. The incorporation of unintentional impurities, such as oxygen, was found by secondary ion mass spectroscopy (SIMS) to be mitigated to similar to 1 x 1019 and similar to 7 x 10(19)cm(-3) on the gallium and nitrogen polar faces, respectively. Published by Elsevier B.V.