Market for Bulk GaN Crystals.- Development of the Bulk GaN Substrate Market.- Vapor Phase Growth Technology.- Hydride Vapor Phase Epitaxy of GaN.- Growth of Bulk GaN Crystals by HVPE on Single Crystalline GaN Seeds.- Freestanding GaN Wafers by Hydride Vapor Phase Epitaxy Using Void-Assisted Separation Technology.- Nonpolar and Semipolar GaN Growth by HVPE.- High Growth Rate MOVPE.- Solution Growth Technology.- Ammonothermal Growth of GaN Under Ammono-Basic Conditions.- A Pathway Toward Bulk Growth of GaN by the Ammonothermal Method.- Acidic Ammonothermal Growth Technology for GaN.- Flux Growth Technology.- High Pressure Solution Growth of Gallium Nitride.- A Brief Review on the Na-Flux Method Toward Growth of Large-Size GaN Crystal.- Low Pressure Solution Growth of Gallium Nitride.- Characterization of GaN Crystals.- Optical Properties of GaN Substrates.- Point Defects and Impurities in Bulk GaN Studied by Positron Annihilation Spectroscopy.