Observation of nanopipes in edge-defined film-fed grown β-Ga2O3 substrate and their effect on homoepitaxial surface hillocks

β-Ga2O3 substrates and homoepitaxial films were characterized using the multiphoton excitation photoluminescence (MPPL) method. MPPL emission peaks at 3.2 and 3.36 eV were obtained with broad shoulders on the low energy side. MPPL images showed the presence of nanopipes in the substrate with a unique contrast. Three-dimensional MPPL imaging revealed the distribution and spatial location of the nanopipes. All the nanopipes were elongated along the [010] direction with diameters of approximately 0.4–1.0 μm and lengths of 10–30 μm. The nanopipes were aligned in the [100] and [001] directions with sub-micron spacing in the (0 1 ¯ 0)-oriented substrate. The nanopipes were located under the hillocks at the homoepitaxial surface. The nanopipes are suggested to trigger the hillock growth by transforming into threading dislocations in the homoepitaxial film.