High densities of threading dislocations (TDs) arising from lattice mismatch between III-nitride films and foreign substrates (e.g., AlN on Si with 19% misfit) significantly impede the efficiency of advanced electronic and optoelectronic devices. This work presents a comparative study investigating the initial growth stages and defect formation mechanisms in InGaN and AlN layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE), Atomic Layer Deposition (ALD), and Physical Vapour Deposition (PVD) techniques, including sputtering. Through comprehensive surface analysis using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), we observed that MOVPE-grown materials consistently developed V-pits, whose crystallographic orientation and density were directly correlated with underlying TDs. In contrast, PVD films typically exhibited growth islands, while ALD depositions under the studied conditions resulted in amorphous layers characterized by high surface roughness and significant contamination.
Transmission Electron Microscopy (TEM) provided critical insights into internal defect structures and strain relaxation. MOVPE-grown AlN films showed varying TD types (a-type edge, a+c-type mixed, c-type screw), with optimized two-step growth processes and controlled deposition rates notably reducing overall TD densities from >1010 cm⁻² to as low as 1.75×109 cm⁻². For InGaN, large V-pits were definitively linked to a+c-type mixed TDs, while smaller V-pits originated from basal stacking faults transforming into a-type edge dislocations. Conversely, PVD-grown AlN was predominantly polycrystalline with dislocations primarily confined to grain boundaries. Electron Beam Induced Current (EBIC) measurements confirmed that specific TD types, particularly a+c-type mixed and c-type screw TDs, act as potent recombination centres of charge carriers. Large V-pits were attributed to c-type dislocations exhibiting the highest recombination activity, which directly impairing device performance.
This research provides crucial comparative understanding of defect generation across varied III-nitride growth methodologies. It highlights pathways for manipulating TD nucleation which may ultimately enhance the efficiency of III-nitride-based semiconductor devices.