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Optimizing thermal anneals of Si-implanted β-Ga2O3 is critical for low resistance contacts and selective area doping. We report the impact of annealing ambient, temperature, and time on the activation of room temperature ion-implanted Si in β-Ga2O3 at concentrations from 5 × 1018 to 1 × 1020 cm−3, demonstrating full activation (>80% activation, mobilities >70 cm2/V s) with contact resistances below 0.29 Ω mm. Homoepitaxial β-Ga2O3 films, grown by plasma-assisted molecular beam epitaxy on Fe-doped (010) substrates, were implanted at multiple energies to yield 100 nm box profiles of 5 × 1018, 5 × 1019, and 1 × 1020 cm−3. Anneals were performed in an ultra-high vacuum-compatible quartz furnace at 1 bar with well-controlled gas compositions. To maintain β-Ga2O3 stability, pO2 must be greater than 10−9 bar. Anneals up to pO2 = 1 bar achieve full activation at 5 × 1018 cm−3, while 5 × 1019 cm−3 must be annealed with pO2 ≤ 10−4 bar, and 1 × 1020 cm−3 requires pO2 < 10−6 bar. Water vapor prevents activation and must be maintained below 10−8 bar. Activation is achieved for anneal temperatures as low as 850 °C with mobility increasing with anneal temperatures up to 1050 °C, though Si diffusion has been reported above 950 °C. At 950 °C, activation is maximized between 5 and 20 min with longer times resulting in decreased carrier activation (over-annealing). This over-annealing is significant for concentrations above 5 × 1019 cm−3 and occurs rapidly at 1 × 1020 cm−3. Rutherford backscattering spectrometry (channeling) suggests that damage recovery is seeded from remnant aligned β-Ga2O3 that remains after implantation; this conclusion is also supported by scanning transmission electron microscopy showing retention of the β-phase with inclusions that resemble the γ-phase. [ABSTRACT FROM AUTHOR]

III-nitrides have revolutionized lighting technology and power electronics. Expanding the nitride semiconductor family to include heterovalent ternary nitrides opens up new and exciting opportunities for device design that may help overcome some of the limitations of the binary nitrides. However, the more complex cation sublattice also gives rise to new interactions with both native point defects and defect complexes that can introduce disorder on the cation sublattice. Here, depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy measurements of defect energy levels in ZnGeN2 combined with transmission electron microscopy and x-ray diffraction reveal optical signatures of mid-gap states that can be associated with cation sublattice disorder. The energies of these characteristic optical signatures in ZnGeN2 thin films grown by metal–organic chemical vapor deposition are in good agreement with multiple, closely spaced band-like defect levels predicted by density functional theory. We correlated spatially resolved optical and atomic composition measurements using spatially resolved x-ray photoelectron spectroscopy with systematically varied growth conditions on the same ZnGeN2 films. The resultant elemental maps vs defect spectral energies and intensities suggest that cation antisite complexes (ZnGe–GeZn) form preferentially vs isolated native point defects and introduce a mid-gap band of defect levels that dominate electron–hole pair recombination. Complexing of ZnGe and GeZn antisites manifests as disorder in the cation sub-lattice and leads to the formation of wurtzitic ZnGeN2 as indicated by transmission electron microscopy diffraction patterns and x-ray diffraction reciprocal space maps. These findings emphasize the importance of growth and processing conditions to control cation place exchange. [ABSTRACT FROM AUTHOR]

SrTiO3 has many applications involving interfaces with other materials, but defects that affect the properties of SrTiO3 films can also play a significant role at its heterointerfaces and even at junctions with nonstoichiometric SrTiO3. Depth-resolved cathodoluminescence spectroscopy (DRCLS) combined with systematic cation Sr content reduction in SrxTiO3 ultrathin films grown on SrTiO3 showed an interplay of native point defects and electronic structure within the Sr-deficient film and how interplay extends tens of nanometers into the substrate below. Understanding how defects form and affect interface electronic structure during epitaxial growth is central to improving complex oxide devices. Controlling the balance of oxygen vacancy defects with strontium vacancies and other acceptor-like defects can improve control over free carrier densities. Likewise, control over nanoscale defect charge distributions can advance new device features such as two-dimensional hole gases and the performance of existing devices such as ferroelectric tunnel junctions. This study shows how DRCLS directly measures the relative densities and spatial distributions of multiple native defects within and extending away from nanoscale SrxTiO3/SrTiO3 junctions and how their interplay varies with controlled epitaxial growth. In turn, these growth-dependent defect variations can help guide SrTiO3 epitaxial growth with other complex oxides. [ABSTRACT FROM AUTHOR]

A predicted type-II staggered band alignment with an approximately 1.4 eV valence band offset at the ZnGeN2/GaN heterointerface has inspired novel band-engineered III-N/ZnGeN2 heterostructure-based device designs for applications in high performance optoelectronics. We report on the determination of the valence band offset between metalorganic chemical vapor deposition grown (ZnGe)1−xGa2xN2, for x = 0 and 0.06, and GaN using x-ray photoemission spectroscopy. The valence band of ZnGeN2 was found to lie 1.45–1.65 eV above that of GaN. This result agrees well with the value predicted by first-principles density functional theory calculations using the local density approximation for the potential profile and quasiparticle self-consistent GW calculations of the band edge states relative to the potential. For (ZnGe)0.94Ga0.12N2 the value was determined to be 1.29 eV, ∼10%–20% lower than that of ZnGeN2. The experimental determination of the large band offset between ZnGeN2 and GaN provides promising alternative solutions to address challenges faced with pure III-nitride-based structures and devices. [ABSTRACT FROM AUTHOR]