The Optical and Electrical Studies of Defects and Impurities in Iso-doped GaN and AlGaN
The progresses in nitride-based optoelectronic developments of wide-band-gap semiconductors have been very significant over the last decade, owing to the advent of the number of techniques. However, In regard to the film quality, the GaN layer contains several defects such as threading dislocations (TD), stacking faults, and inversion domain boundaries (IDBs) because of a large lattice mismatch and thermal expansion coefficient difference between GaN and sapphire. As we known, the defect density is up to ~ 1016 cm-2 that strongly affect most optical and electrical properties of GaN. While there are some progress in the device fabrications, the luminescence mechanism in GaN and AlGaN is still under intense investigation, especially how the structural and compositional inhomogeneities in the alloy affect optical properties. For example, whether defects act as nonradiative recombination centers or enhance the compositional fluctuation which induces localized exciton states to give strong emission needs to be clarified. Furthermore, these defects such as threading dislocations and point defects inside the material would penetrate from the buffer layer into the surface forming surface structures. In recent years, there has been remarkably rapid progress in the development of micro-measurement technology. Surface V-shape defect formed on the GaN is still a problem. These V defects are an open hexagonal, inverted pyramid with (101-1) side walls. Due to the difference observed between the surface structure and bulk region, much interest has focused on the micro-structure research. However, the previous studies of the origin of V defects are mainly from the AFM or STM images of InGaN/GaN MQWs and there have been very few studies on the optical and electrical properties of V-pits in AlGaN and GaN. Therefore, we attempted to investigate surface defects by the optical characterization and develop a new method to identify and show the properties of surface states.