Approximately 4-µm-thick GaN epitaxial films were directly grown onto a GaN/sapphire template, sapphire, Si(111), and Si(100) substrates by high-temperature pulsed laser deposition (PLD). The influence of the substrate type on the crystalline quality, surface morphology, microstructure, and stress states was investigated by X-ray diffraction (XRD), photoluminescence (PL), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman spectroscopy. Raman scattering spectral analysis showed a compressive film stress of −0.468 GPa for the GaN/sapphire template, whereas the GaN films on sapphire, Si(111), and Si(100) exhibited a tensile stress of 0.21, 0.177, and 0.081 GPa, respectively. Comparative analysis indicated the growth of very close to stress-free GaN on the Si(100) substrate due to the highly directional energetic precursor migration on the substrate's surface and the release of stress in the nucleation of GaN films during growth by the high-temperature (1000 • C) operation of PLD. Moreover, TEM images revealed that no significant GaN meltback (Ga-Si) etching process was found in the GaN/Si sample surface. These results indicate that PLD has great potential for developing stress-free GaN templates on different substrates and using them for further application in optoelectronic devices.

In this study, we investigated the microstructure and optical properties of hexagonal GaN (h-GaN) films grown by high-temperature pulsed laser deposition (PLD) on Si(100) and Si(111) substrates. The growth mechanism, crystallization, and surface morphology of h-GaN deposition on both Si(100) and Si(111) substrates were monitored by transmission electron microscopy (TEM) and scanning electron microscopy at various times in the growth process. Our results indicated that the h-GaN grown on Si(111) has better crystalline structure and optical properties than that on Si(100) owing to the smaller mismatch of the orientations of the Si(111) substrate and h-GaN film. On the Si(100) substrate, the growth principles of PLD and N2 plasma nitridation are the main contributions to the conversion of the cubic GaN into h-GaN. Moreover, no significant Ga–Si meltback etching was observed on the GaN/Si surface with the PLD operation temperature of 1000 °C. The TEM images also revealed that an abrupt GaN/Si interface can be obtained because of the suppression of substrate–film interfacial reactions in PLD.