Continued development of GaN-based light emitting diodes is being hampered by constraints imposed by current non-native substrates. ZnO is a promising alternative substrate but it decomposes under the conditions used in conventional GaN metal organic vapor phase epitaxy (MOVPE). In this work, GaN was grown on $\mathrm{Zn}\mathrm{O}∕c\text{-}{\mathrm{Al}}_2{\mathrm{O}}_3$ using low temperature/pressure MOVPE with ${\mathrm{N}}_2$ as a carrier and dimethylhydrazine as a $N$ source. Characterization confirmed the epitaxial growth of GaN. The GaN was lifted-off the $c\text{-}{\mathrm{Al}}_2{\mathrm{O}}_3$ by chemically etching away the ZnO underlayer. This approach opens up the way for bonding of the GaN onto a support of choice.

Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that ($\overline{2}01$ ) oriented β-Ga₂O₃ has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on ($\overline{2}01$ ) oriented β-Ga₂O₃ are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼10⁸cm⁻². X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on ($\overline{2}01$ ) β-Ga₂O₃ with in-plane epitaxial orientation relationships between the β-Ga₂O₃ and the GaN thin film defined by (010) β-Ga₂O₃ || ($11\overline{2}0$ ) GaN and ($\overline{2}01$ ) β-Ga₂O₃ || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high.

The radiation damage formation upon low temperature ion implantation and neutron irradiation has been compared for GaN and ZnO. Both materials exhibit strong dynamic annealing effects during implantation, even at 15 K, leading to high amorphisation thresholds. The damage build-up with fluence was found to proceed in a similar way for GaN and ZnO, both showing two saturation regimes below the amorphisation level where, over wide fluence regions, the damage level increases only very slowly. For low fluences the damage accumulation rate is similar for both materials. For higher fluences, on the other hand, GaN shows considerably higher damage levels and finally collapses into an amorphous structure while ZnO remains single crystalline up to the highest fluence of 7×10¹⁶ Ar/cm². Neutron irradiation produces similar defects as ion implantation but within the entire sample while the defect density is much lower. The main effect of irradiation on the structural properties of GaN is an expansion of the c-lattice parameter. Optical properties are significantly deteriorated after irradiation and only recover partially after annealing. ZnO does not suffer such a pronounced change of the lattice parameters but reveals a strong deterioration of the surface, possibly due to blistering and exfoliation. At the same time the optical properties are less affected than for GaN. The near band edge emission is partly quenched but recovers to a large extend after annealing while broad defect bands are observed below the bandgap for irradiated samples, before and after annealing.