GaN Characterization by X-ray Techniques

Gallium nitride (GaN) is a binary III/V direct bandgap semiconductor. In recent years, due to its unique characteristics such as hard, mechanically stable, superior carrier saturation velocity, high heat capacity, and thermal conductivity, GaN is widely applied in the advanced fabrication of bright light-emitting diodes, optoelectronics, high-power and high frequency electronic devices. However, large differences in the coefficient of thermal expansion and lattice constant between GaN epitaxial layers and a substrate exist. These thermal mismatch and lattice mismatch lead to strain and the generation of defects in the GaN and affect the performance of the devices. Techniques of X-ray diffraction are applied for characterization: reciprocal space mapping is applied to analyze strain and relaxation in epitaxial layers; high resolution rocking curves are applied for dislocation density calculation; and X-ray reflectivity is also applied to characterize the thickness and roughness information. For structural simulation of the GaN-based devices, software LEPTOS is applied.