Structural characterization of thick GaN films grown on free-standing GaN seeds by the ammonothermal method using basic ammonia

Single crystalline GaN was grown on c-plane free-standing GaN seeds via fluid transport by the ammonothermal method. Ammonothermal growth was carried out in an ammonobasic solution with a metallic Ga nutrient placed in a lower-temperature zone. The thickest film obtained so far is similar to 45 mu m, which was grown on the N-face of the seed. The growth interface contained numerous voids and defects, whereas the microstructure close to the surface was greatly improved. The major defects close to the surface were mixed-character threading dislocations. The estimated threading dislocation density was low-10(9) cm(-2) level at the free surface of the N-face.