Studies on structural and optical gap tunability in α-(Ga x Cr(1-x))2O3 solid solutions

Highlights: • Synthesis of α-(Ga_xCr_(1-x))₂O₃ (0 ≤ x ≤ 0.45) by solid sate reaction method. • Deviation of lattice parameters from the Vegard's law and immiscibility of Ga is discussed. • Tunability of ∼0.5 eV in the bandgap of α-Cr₂O₃ as a function of Ga composition. • Enhancement in the mixing of Cr d and O 2p states in the valance band. We report the structural and optical properties of ternary α-(Ga_xCr_(1-x))₂O₃ with 0 ≤ x ≤ 0.45 which is synthesized by solid state reaction method. Single phase with space group R-3c is obtained for the gallium composition range of 0 ≤ x ≤ 0.45 and further increase in Ga concentration results in appearance of secondary C2/m phase corresponds to Ga₂O₃. Variations in the in-plane 'a' and out of plane 'c' lattice parameters shows a clear daviation from the Vegard's law with the bowing parameters of −0.0510 Å and 0.0305 Å respectively. Extended X-ray absorption fine structure (EXAFS) spectroscopy shows larger values of Ga-O bond lengths, which elucidate the deviation in lattice parameters from the Vegard's law and immisibility of Ga in Cr₂O₃ lattice. Diffuse reflectance spectroscopy (DRS) confirms a blue shift of 0.5 eV in the band gap of α-(Ga_xCr_(1-x))₂O₃. It has also observed that Cr 3d level shifted towards the O 2p level in the valence band which has been reconfirmed by photo electron spectroscopy. The observed shift indicates enhancement of mixing between these levels which can leads to further delocalization of hole states in the valence band responsible for p-type conduction in the α-Cr₂O₃. These results suggest that ternary α-(Ga_xCr_(1-x))₂O₃ (0 ≤ x ≤ 0.45) can be useful in the field of UV transperant electronics and photodetectors.