The lattice distortion and epitaxial nature of β-Ga 2 O 3 layers deposited on GaN templates using radio-frequency magnetron sputtering have been evaluated. The determined values of out-of-plane (tensile type) and in-plane (compressive type) strain are found to decrease with increase in deposition temperature, indicating better relaxation of the unit cell lattice at higher temperatures. The obtained value of angle β is invariably higher than its bulk value, suggesting a distortion in the unit cell of β-Ga 2 O 3 layer. Columnar-type growth for β-Ga 2 O 3 layer on GaN template has been observed. Analysis of its epitaxial nature reveals that six domains of grown layer are in-plane rotated by 60 • ± δ o (δ = 2 • -3 • ) with each other, which is explained by the presence of three non-equivalent oxygen atoms on the (−201) plane of β-Ga 2 O 3 . The calculated values of δ nearly match experimentally observed values. However, the smaller difference between the two is related to residual strain in the layer. The out-of-plane and in-plane epitaxial relationship for β-Ga 2 O 3 layer with respect to GaN are (−201) Ga2O3 || (0001) GaN and (010) Ga2O3 || (11-20) GaN , respectively.
Oriented thin films of β-(Ga1-xFex)2O3 have been deposited by RF magnetron sputtering on c-Al2O3 and GaN substrates. The itinerant character of Fe 3d states forming the top of the valence band (VB) of Fe substituted of β-Ga2O3 thin films has been determined from resonant photoelectron spectroscopy (RPES). Further, admixture of itinerant and localized character of these Fe 3d sates is obtained for larger binding energies i.e deeper of VB. The bottom of the conduction band (CB) for β-(Ga1-xFex)2O3 is also found to be strongly hybridized states involving Fe 3d and O 2p states as compared to that of Ga 4s in pristine β-Ga2O3. This suggests that β-Ga2O3 transforms from band like system to a charge transfer system with Fe substitution. Furthermore, the bandgap red shits with Fe composition, which has been found to be primarily related to the shift of the CB edge.
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