GaN freestanding substrate was obtained by hydride vapor phase epitaxy directly on sapphire with porous network interlayer. The morphologies of Ga-face and N-face of freestanding GaN substrate were analyzed by a variety of characterization techniques before and after etching in boiled KOH for 1 min. The obtained characteristics of unetched GaN are strongly dependent on the growth polarity. The N-polar GaN layer has high free electron, impurity and point defect concentrations. In the layers grown on the (0 0 0 1) Ga-polar side, these concentrations are very low. After etching, the Ga-polar GaN ...
