UCLA

Aluminium Nitride (AlN) thin-films have been long used as a buffer layer on substrates to grow Gallium Nitride (GaN) for high power transistors. Researchers recently have started studying using AlN itself as an electronic material due to its higher band gap compared to GaN and applications in UV light source for photolithography systems. One of the main challenges of growing AlN on traditional substrates like Silicon (Si) is the large lattice mismatch and difference in crystal structures. Both these effects lead to strained and lower quality thin-films.This study discusses the procedure for performing high-resolution X-ray diffraction (HRXRD) measurements, discussing equipment setup and choosing the diffraction peaks that are most suitable for this analysis. Symmetric and asymmetric scans were performed to calculate out-of-plane and in-plane strains respectively. Analysis of the full-width at half-maximum (FWHM) was done to qualitatively compare the film-quality for different samples. This study analyzes the strain and film quality for AlN thin-films grown on Si. Two sets of samples have been analyzed – one with AlN thin-films grown on bare Si and second with a GaN nanowire interlayer between AlN and Si. The GaN nanowire layer serves to reduce the strain present in AlN by lowering the lattice mismatch compared to Si. All measurements have been performed using (HRXRD). Results show that samples with GaN interlayer have an almost completely relaxed AlN layer with better film quality compared to those grown on bare Si. The strain ranges from 0% to 0.3% for samples with GaN interlayer while AlN on bare Si sample has a strain of about 1%. For samples with the GaN layer, different thicknesses have been analyzed. Results indicate that the thicker layers are more strained and have a lower film quality. AlN films grown on bare Si were characterized for surface roughness and thickness using X-ray reflectivity (XRR). Data shows that the surface has a roughness of about 3 nm with the films being 200 nm thick. The presence of a GaN nanowire interlayer has shown to improve the AlN thin-films grown on Si, further paving the way for this material to be used in electronic applications.