Epitaxial structure and electronic property of β -Ga₂O₃ films grown on MgO (100) substrates by pulsed-laser deposition

We investigated heteroepitaxial growth of Si-doped Ga₂O₃ films on MgO (100) substrates by pulsed-laser deposition as a function of growth temperature (T_g) to find a strong correlation between the structural and electronic properties. The films were found to contain cubic γ-phase and monoclinic β-phase, the latter of which indicated rotational twin domains when grown at higher T_g. The formation of the metastable γ-phase and twin-domain structure in the stable β-phase are discussed in terms of the in-plane epitaxial relationships with a square MgO lattice, while crystallinity of the β-phase degraded monotonically with decreasing T_g. The room-temperature conductivity indicated a maximum at the middle of T_g, where the β-Ga₂O₃ layer was relatively highly crystalline and free from the twin-domain structure. Moreover, both crystallinity and conductivity of β-Ga₂O₃ films on the MgO substrates were found superior to those on α-Al₂O₃ (0001) substrates. A ratio of the conductivity, attained to the highest quantity on each substrate, was almost three orders of magnitude.