Much research in the past five decades has been done on the group III nitrides (III-N) comprising the Al-Ga-In-N alloys, which have a characteristic wide bandgap necessary for many applications, such as short-wavelength visible-light emission [1-3]. The success of the nitride semiconductor technology rests significantly on the control of its microstructure [4,5]. The early development of these materials dates back from the growth of AlN in 1907 [6] to the successful epitaxial growth of GaN in 1969 [7]. Some of the key steps in the development of the III-N semiconductors, which culminated with the demonstration of blue and ultraviolet diode lasers in 1996, are listed in Table 2.1.