Radiation tolerance is determined as the ability of crystalline materials to withstand the accumulation of the radiation induced disorder. Nevertheless, for sufficiently high fluences, in all by far known semiconductors it ends up with either very high disorder levels or amorphization. Here we show that gamma/beta (γ/β) double polymorph Ga₂O₃ structures exhibit remarkably high radiation tolerance. Specifically, for room temperature experiments, they tolerate a disorder equivalent to hundreds of displacements per atom, without severe degradations of crystallinity; in comparison with, e.g., Si amorphizable already with the lattice atoms displaced just once. We explain this behavior by an interesting combination of the Ga- and O- sublattice properties in γ-Ga₂O₃. In particular, O-sublattice exhibits a strong recrystallization trend to recover the face-centered-cubic stacking despite the stronger displacement of O atoms compared to Ga during the active periods of cascades. Notably, we also explained the origin of the β-to-γ Ga₂O₃ transformation, as a function of the increased disorder in β-Ga₂O₃ and studied the phenomena as a function of the chemical nature of the implanted atoms. As a result, we conclude that γ/β double polymorph Ga₂O₃ structures, in terms of their radiation tolerance properties, benchmark a class of universal radiation tolerant semiconductors.

Polymorphs are common in nature and can be stabilized by applying external pressure in materials. The pressure and strain can also be induced by the gradually accumulated radiation disorder. However, in semiconductors, the radiation disorder accumulation typically results in the amorphization instead of engaging polymorphism. By studying these phenomena in gallium oxide we found that the amorphization may be prominently suppressed by the monoclinic to orthorhombic phase transition. Utilizing this discovery, a highly oriented single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated. Exploring this system, a novel mode of the lateral polymorphic regrowth, not previously observed in solids, was detected. In combination, these data envisage a new direction of research on polymorphs in ${\mathrm{Ga}}_2{\mathrm{O}}_3$ and, potentially, for similar polymorphic families in other materials.

A superior micron-sized inverted pyramid structure has been successfully achieved by one-step copper nanoparticles assisted chemical etching in Si/Cu(NO₃)₂/HF/H₂O₂ solution for light trapping in silicon solar cells. The detailed mechanisms of such a novel method have been systematically demonstrated. The charge transfer during the reaction has been revealed by the simplified energy band diagram of the system as well. In order to form micro-structured inverted pyramids, the generation and dissolution of Cu nanoparticles should keep in balance during the reaction, which depends on the concentration of the etchant, the doping type and the doping level of the silicon substrate. With the investigation of the intrinsic properties of the silicon substrate, the etching rate is found out as a combined result of the electron concentration and the defect density of the substrate, as well as the potential barrier on the interface of Si/Cu nanoparticles. Furthermore, the anisotropic nature of Cu assisted chemical etching has also been investigated.

The role of vacancy clustering and acceptor activation on resistivity evolution in N ion-implanted $n$-type hydrothermally grown bulk ZnO has been investigated by positron annihilation spectroscopy, resistivity measurements, and chemical profiling. Room temperature $220\mathrm{keV}$ N implantation using doses in the low ${10}^{15}{\mathrm{cm}}^{-2}$ range induces small and big vacancy clusters containing at least 2 and 3–4 Zn vacancies, respectively. The small clusters are present already in as-implanted samples and remain stable up to $1000°\mathrm{C}$ with no significant effect on the resistivity evolution. In contrast, formation of the big clusters at $600°\mathrm{C}$ is associated with a significant increase in the free electron concentration attributed to gettering of amphoteric Li impurities by these clusters. Further annealing at $800°\mathrm{C}$ results in a dramatic decrease in the free electron concentration correlated with activation of ${10}^{16}–{10}^{17}{\mathrm{cm}}^{-3}$ acceptors likely to be N and/or Li related. The samples remain $n$ type, however, and further annealing at $1000°\mathrm{C}$ results in passivation of the acceptor states while the big clusters dissociate.

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