I will address the fundamental question as to why the performance of Optoelectronic devices based on nitride semiconductors is insensitive to high concentration of extended defects, which is not the case for traditional III-V compounds. I will discuss three important differences between these two families of materials, which contribute to this finding: (a) the chemical bonds in nitrides are strongly ionic while are mostly covalent in III-V compounds. This leads to the bunching of the intrinsic surface states as well as the states associated with dangling bonds in edge dislocations near the band edges where they act as traps rather than recombination centers. Furthermore, the surface states have less effect on the surface Fermi level position; (b) the nitrides can exist in the wurtzite structure (equilibrium) and the cubic structure (metastable) and the enthalpy of formation of the two allotropic forms differs by only a few meV. Thus, conversion between the two phases occurs easily by creation of stacking faults along the close-packed (0001) and (111) planes, which due to the smaller energy gap of the cubic phase leads to strong band structure potential fluctuations in the wurtzite matrix; (c) additional band structure potential fluctuations exist in the InGaAlN alloys due to alloy disorder as well as phase separation and unique types of long range atomic ordering. The potential fluctuations discussed in (b) and (c) contribute to exciton localization and thus, efficient radiative recombination even at room temperature.
