The majority of III-N are grown along the polar c-axis of the wurtzite structure, leading to an enhanced carrier separation due to polarization-induced electrostatic fields of the order of MV/cm. A promising approach preventing such effects is the growth along semipolar orientations, i.e. planes with a nonzero h, k, or i and a nonzero l Miller index. A fascinating feature of the semipolar planes is that depending on their orientation they may exhibit either Ga-polar or N-polar “flavor” and on the same time lye close to m- or a-plane non-polar character. However, it is still an open question whether the extensive experience gathered from the growth of polar and/or non-polar planes can be applied to the semipolar planes or whether novel atomistic mechanisms dominate the growth. A prerequisite to achieve smooth semipolar surface morphologies and high quality material is to gather a deep understanding of the atomistic mechanisms governing the growth of these surfaces.
A prerequisite towards achieving biological and chemical sensing applications is to to investigate, understand and quantify the effect of the absorbants on the electronic structure of surfaces. Surface states at semiconductors influence the electronic properties of devices and heterostructures since they can induce Fermi level pinning and bending of the conduction and valence band at the surface and at the interfaces.
One of the controversial issues in the field of III-Nitrides is the effect dislocations have on the optoelectronic properties of the devices. For edge dislocations, we have shown in an earlier study that even in the case of fully coordinated cores the huge strain field around the dislocation line introduces deep states in the bandgap. The strain field of screw type dislocations is characterized by non-zero shear components and has been proposed to result in hole localization.
Surfactants and antisurfactants are species, deposited prior to growth on the substrate to overcome fundamental limitations set by thermodynamics and adatom kinetics in a particular heteroepitaxial system. The role and mechanisms of surfactants and self-surfactants in the growth of group III-Nitrides is well established and understood. However, the physics governing the technological important example of Si as antisurfactant in GaN was under intensive debate.