β-Ga2O3 is a wide bandgap semiconductor that is attractive for various applications, including power electronics, transparent conductive electrodes, etc. Electrical and optical properties of Ga2O3 are affected by the presence of dopants/contaminants and/or intrinsic defects. Here, we investigate the electrical and optical properties of transition metals like Co and Cr since they are often unintentionally present during the growth or used as intentional dopants. This is done by using magnetic resonance spectroscopy and magneto-optical characterization techniques. We determine spin- Hamiltonian parameters of the Cr3+ ground-state and first excited-state as well as the spin-Hamiltonian parameters of Co2+.

GaAs-based semiconductors are highly attractive for diverse nonlinear photonic applications, owing to their non-centrosymmetric crystal structure and huge nonlinear optical coefficients. Nanostructured semiconductors, for example, nanowires (NWs), offer rich possibilities to tailor nonlinear optical properties and further enhance photonic device performance. In this study, it is demonstrated highly efficient second-harmonic generation in subwavelength wurtzite (WZ) GaAs NWs, reaching 2.5 × 10⁻⁵ W⁻¹, which is about seven times higher than their zincblende counterpart. This enhancement is shown to be predominantly caused by an axial built-in electric field induced by spontaneous polarization in the WZ lattice via electric field-induced second-order nonlinear susceptibility and can be controlled optically and potentially electrically. The findings, therefore, provide an effective strategy for enhancing and manipulating the nonlinear optical response in subwavelength NWs by utilizing lattice engineering.

We report on optimization of growth conditions of GaAs/GaNAs/GaAs core/shell/shell nanowire (NW) structures emitting at ~1 μm, aiming to increase their light emitting efficiency. A slight change in growth temperature is found to critically affect optical quality of the active GaNAs shell and is shown to result from suppressed formation of non-radiative recombination (NRR) centers under the optimum growth temperature. By employing the optically detected magnetic resonance spectroscopy, we identify gallium vacancies and gallium interstitials as being among the dominant NRR defects. The radiative efficiency of the NWs can be further improved by post-growth annealing at 680 °C, which removes the gallium interstitials.

Nanowires (NWs) based on ternary GaAsP and quaternary GaNAsP alloys are considered as very promising materials for optoelectronic applications, including in multi-junction and intermediate band solar cells. The efficiency of such devices is expected to be largely controlled by grown-in defects. In this work we use the optically detected magnetic resonance (ODMR) technique combined with photoluminescence measurements to investigate the origin of point defects in Ga(N)AsP NWs grown by molecular beam epitaxy on Si substrates. We identify gallium vacancies, which act as non-radiative recombination centers, as common defects in ternary and quaternary Ga(N)AsP NWs. Furthermore, we show that the presence of N is not strictly necessary for, but promotes, the formation of gallium vacancies in these NWs.

We report on the first successful growth of wurtzite (WZ) GaBiAs nanowires (NWs) and reveal the effects of Bi incorporation on the electronic band structure by using polarization-resolved optical spectroscopies performed on individual NWs. Experimental evidence of a decrease in the band-gap energy and an upward shift of the topmost three valence subbands upon the incorporation of Bi atoms is provided, whereas the symmetry and ordering of the valence band states remain unchanged, that is, Γ9, Γ7, and Γ7 within the current range of Bi compositions. The extraordinary valence band structure of WZ GaBiAs NWs is explained by anisotropic hybridization and anticrossing between p-like Bi states and the extended valence band states of host WZ GaAs. Moreover, the incorporation of Bi into GaAs is found to significantly reduce the temperature sensitivity of the band-gap energy in WZ GaBiAs NWs. Our work therefore demonstrates that utilizing dilute bismide alloys provides new avenues for band-gap engineering and thus photonic engineering with NWs.

One-dimensional ZnO nanowires are a promising material system for a wide range of optoelectronic and photonic applications. Utilization of ZnO, however, requires high-quality ZnO with reliable n-type and p-type conductivity, with the latter remaining elusive, so far. In this work we report on effects of N doping via ion implantation on defect formation in ZnO nanowires studied by optically detected paramagnetic resonance (ODMR) spectroscopy complemented by photoluminescence spectroscopy. After N implantation, zinc interstitial shallow donors, which are formed as a result of ion implantation, are observed in addition to effective mass type shallow donors. Additionally, ODMR signals related to oxygen vacancies can be observed. Implantation also causes formation of a new nitrogen related defect center, which acts as an acceptor. The present findings are of importance for understanding impacts of different defects and impurities on electronic properties of nanostructured ZnO and achieving p-type conductivity via nitrogen doping.

Gallium oxide (β-Ga2O3) is a wide-bandgap compound semiconductor with a bandgap of ∼4.9 eV that is currently considered promising for a wide range of applications ranging from transparent conducting electrodes to UV optoelectronic devices and power electronics. However, all of these applications require a reliable and precise control of electrical and optical properties of the material, which can be largely affected by impurities, such as transition metals commonly present during the growth. In this work, we employ electron paramagnetic resonance (EPR) spectroscopy to obtain EPR signatures of the 3d-transition metals Co2+ and Cu2+ in β-Ga2O3 bulk crystals and powders that were unknown so far. Furthermore, we show that both Co2+ and Cu2+ preferentially reside on the octahedral gallium lattice site.

Oxaliplatin typically causes acute neuropathic problems, which may, in a dose-dependent manner, develop into a chronic form of chemotherapy-induced peripheral neuropathy (CIPN), which is associated with retention of Pt2+ in the dorsal root ganglion. A clinical study by Coriat and co-workers suggests that co-treatment with mangafodipir [Manganese(II) DiPyridoxyl DiPhosphate; MnDPDP] cures ongoing CIPN. These authors anticipated that it is the manganese superoxide dismutase mimetic activity of MnDPDP that explains its curative activity. However, this is questionable from a pharmacokinetic perspective. Another, but until recently undisclosed possibility is that Pt2+ outcompetes Mn2+/Ca2+/Zn2+ for binding to DPDP or its dephosphorylated metabolite PLED (diPyridoxyL EthylDiamine) and transforms toxic Pt2+ into a non-toxic complex, which can be readily excreted from the body. We have used electron paramagnetic resonance guided competition experiments between MnDPDP (10logKML ≈ 15) and K2PtCl4, and between MnDPDP and ZnCl2 (10logKML ≈ 19), respectively, in order to obtain an estimate the 10logKML of PtDPDP. Optical absorption spectroscopy revealed a unique absorption line at 255 nm for PtDPDP. The experimental data suggest that PtDPDP has a higher formation constant than that of ZnDPDP, i.e., higher than 19. The present results suggest that DPDP/PLED has a high enough affinity for Pt2+ acting as an efficacious drug in chronic Pt2+-associated CIPN.