Wurtzite AlGaN is a wide band gap semiconductor alloy of great importance for optoelectronic devices such as light diodes emitting in the UV range or short wave-length laser diodes, both incorporating GaN/AlGaN epitaxial multilayers. Due to different lattice constants of AlN and GaN, the heteroepitaxy leads to either strained (unrelaxed) layers, fully relaxed layers or most often partially relaxed layers (the latter two being defective). As a consequence, the active regions of the devices consisting of several thin layers with varying Al fraction are often under either tensile or compressive strain depending on a particular device design).

Electron energy loss spectroscopy (EELS) performed in a transmission electron microscope offers a high spatial (below 1 nm) and energy (below 0.1 eV with state-of-the-art monochromators) resolution. Its subset, electron energy loss near edge structure (ELNES) is known to reflect the electronic structure of materials. However, a comparison with simulated data is needed for interpretation of the experimental ELNES.

The aim of the project is to investigate the strain effects on projected density of states for several deformation modes and to predict the actual influence on the N K-edge.

Random alloys are modeled using Special Quasirandom Structures. The electronic structure and the energetics of the AlGaN alloys will be calculated for the following deformation modes:

• Uni-axial strain along the c-direction.
• Bi-axial strain in the c-plane.
• Volume conserving bi-axial deformation.
• Bi-axial stress with σ_zz = 0.