Methods for quantifying extended defects in a gallium-containing nitride crystal, wafer, or device, are disclosed. The methods include providing a gallium-containing nitride crystal, wafer, or device, processing the gallium-containing nitride crystal, wafer, or device in an etchant solution comprising one or more of H3PO4, H3PO4 that has been conditioned by prolonged heat treatment to form polyphosphoric acid, and H2SO4; removing the gallium-containing nitride crystal, wafer, or device from the etchant solution; and quantifying the concentration of at least one of etch pits or etch grooves.