β-Ga2O3 is a promising ultrawide bandgap semiconductor for high power and extreme environment applications. The dominant O—H center in Ga2O3 has been assigned to a Ga(1) vacancy–2H (VGa(1)-2H) complex. An analysis of the polarization dependence of the vibrational absorption of the VGa(1)-2D center in monoclinic β-Ga2O3 provides a unique strategy for the determination of both the orientation of the principal dielectric axes in the near infrared and the direction of the vibrational transition moment of the defect.

The ion implantation of H+ and D+ into Ga2O3 produces several O–H and O–D centers that have been investigated by vibrational spectroscopy. These defects include the dominant VGa(1)-2H and VGa(1)-2D centers studied previously along with additional defects that can be converted into this structure by thermal annealing. The polarization dependence of the spectra has also been analyzed to determine the directions of the transition moments of the defects and to provide information about defect structure. Our experimental results show that the implantation of H+ (or D+) into Ga2O3 produces two classes of defects with different polarization properties. Theory finds that these O–H (or O–D) centers are based on two shifted configurations of a Ga(1) vacancy that trap H (or D) atom(s). The interaction of VGa(1)-nD centers with other defects in the implanted samples has also been investigated to help explain the number of O–D lines seen and their reactions upon annealing. Hydrogenated divacancy VGa(1)-VO centers have been considered as an example.

Si is an n-type dopant in Ga2O3 that can be intentionally or unintentionally introduced. The results of Secondary Ion Mass Spectrometry, Hall effect, and infrared absorption experiments show that the hydrogen plasma exposure of Si-doped Ga2O3 leads to the formation of complexes containing Si and H and the passivation of n-type conductivity. The Si-H (D) complex gives rise to an O-H (D) vibrational line at 3477.6 (2577.8) cm−1 and is shown to contain a single H (or D) atom. The direction of the transition moment of this defect has been investigated to provide structure-sensitive information. Theory suggests possible structures for an OH-Si complex that is consistent with its observed vibrational properties.

Substitutional impurities in β-Ga2O3 are used to make the material n-type or semi-insulating. Several O–H and O–D vibrational lines for complexes that involve impurities that are shallow donors and deep acceptors have been reported recently. The present article compares and contrasts the vibrational properties of complexes that involve shallow donors (OD-Si and OD-Ge) with complexes that involve deep acceptors (OD-Fe and OD-Mg). Theoretical analysis suggests that these results arise from defect complexes based on a shifted configuration of the Ga(1) vacancy with a trapped H atom and a nearby impurity.

α-Ga2O3 has the corundum structure analogous to that of α-Al2O3. The bandgap energy of α-Ga2O3 is 5.3 eV and is greater than that of β-Ga2O3, making the α-phase attractive for devices that benefit from its wider bandgap. The O–H and O–D centers produced by the implantation of H+ and D+ into α-Ga2O3 have been studied by infrared spectroscopy and complementary theory. An O–H line at 3269 cm−1 is assigned to H complexed with a Ga vacancy (VGa), similar to the case of H trapped by an Al vacancy (VAl) in α-Al2O3. The isolated VGa and VAl defects in α-Ga2O3 and α-Al2O3 are found by theory to have a “shifted” vacancy-interstitial-vacancy equilibrium configuration, similar to VGa in β-Ga2O3, which also has shifted structures. However, the addition of H causes the complex with H trapped at an unshifted vacancy to have the lowest energy in both α-Ga2O3 and α-Al2O3.