Microstructural Analysis of Void Formation Due to a NH4Cl Layer for Self-Separation of GaN Thick Films

Abstract

The role of a NH(4)Cl layer grown between GaN and a sapphire Substrate for self-separation of GaN films was investigated in detail. Microstructural analysis of the NH(4)Cl layer reveals that self-separation of a GaN film was effectively assisted by the sub-micrometer-sized voids formed due to etching of GaN by evaporated NH(4)Cl. An areal fraction of nonetched GaN in contact with sapphire substrate was found to be linearly dependent on the thickness of NH(4)Cl layer and to have two different proportionality constants below and above an NH(4)Cl thickness at which GaN begins to be self-separated. This intriguing behavior was well explained by a simple model that takes account of void merging.