Magnesium-doped gallium oxide may be utilized as a semi-insulating material for future generations of power devices. Spectroscopy and hybrid functional calculations were used to investigate defect levels in Czochralski-grown β-Ga2O3. Substitutional Mg dopants act as deep acceptors, while substitutional Ir impurities are deep donors. Hydrogen-annealed Ga2O3:Mg shows an IR peak at 3492 cm−1, assigned to an O-H bond-stretching mode of a neutral MgH complex. Despite compensation by Ir and Si and hydrogen passivation, high concentrations of Mg (1019 cm−3) can push the Fermi level to mid-gap or lower.

Gallium oxide is a promising semiconductor for its potential as a material in the field of power electronics. The effects of iridium impurities on undoped, Mg-doped, and Ca-doped gallium oxides were investigated with IR spectroscopy. In undoped and Ca-doped β-Ga2O3, IR peaks at 3313, 3450, and 3500 cm−1 are tentatively assigned to O–H bond-stretching modes of IrH complexes. Mg-, Ca-, and Fe-doped samples show an Ir4+ electronic transition feature at 5148 cm−1. By measuring the strength of this feature vs photoexcitation, the Ir3+/4+ donor level was determined to lie 2.2–2.3 eV below the conduction band minimum. Ga2O3:Mg also has a range of sidebands between 5100 and 5200 cm−1, attributed to IrMg pairs. Polarized IR measurements show that the 5248 cm−1 peak is anisotropic, weakest for light polarized along the c axis, consistent with Lenyk et al. [J. Appl. Phys. 125, 045703 (2019)].

Pyrene is a polycyclic aromatic hydrocarbon with fluorescence in the 370–400 nm range. The optical properties of pyrene deposited on different substrates were investigated from experimental and theoretical points of view. In contrast to prior studies of surface-enhanced fluorescence, in this work, all substrates were semiconductors or insulators. Experimentally, the intensities of photoluminescence (PL) and PL excitation (PLE) spectra were investigated. The PLE spectra of pyrene’s monomer emission show that the intensities of the two main absorption peaks vary according to the chosen substrate. Calculations for pyrene on zinc sulfide (ZnS) and surface-oxidized diamond suggest that this connection arises from the alignment of the pyrene electronic levels relative to the band edges of the substrate. The absorption peak at 272 nm (4.56 eV) is shown to depend on the HOMO-1→LUMO orbital contribution, whereas the 335 nm (3.70 eV) peak depends upon the HOMO→LUMO transition. When the HOMO-1 level falls inside the substrate valence band, as in the case of ZnS, there is significant hybridization of the molecular state with surface states that causes an enhancement of the 272 nm peak. For pyrene on diamond, however, the HOMO-1 level falls in the substrate bandgap, leading to negligible hybridization and thus no enhancement.

ZnS1−xOx alloy films were studied via resonant Raman spectroscopy. Films with a low oxygen content exhibit ZnS longitudinal optical modes and additional modes attributed to O local vibrational modes (LVMs). The frequencies of these modes are explained by a simple mass-defect model. As the O content increases, pairs and larger clusters form, causing the O mode to transition from an LVM to a delocalized phonon. The composition dependence of the modes shows agreement with the modified random element isodisplacement model. Low-temperature measurements show that the O-related mode is composed of multiple features, attributed to zincblende and wurtzite structural regions.

Substitution of O in the ZnS lattice is observed to result in a doublet consisting of two local vibrational modes (LVMs) and a second order harmonic of the LVMs. The first order doublet is attributed to vibrational modes of a defect with trigonal (C3v) symmetry. The results of temperature dependent resonant Raman scattering and anti‐Stokes scattering support this assignment. The substitution of O in the lattice also leads to the presence of LVM + nLO combination modes, which are interpreted in terms of the cascade model and resonance effects.