.2 and V. B. LushchanetsThe dispersion of the refractive index of β-Ga 2 O 3 thin fi lms obtained by RF-sputtering was investigated. Anomalous dispersion was observed for fi lms annealed in hydrogen; normal dispersion, for fi lms annealed in oxygen or argon. The spectral dependence in the visible region of the refractive index with normal dispersion was determined mainly by transitions from the top of the valence band formed by oxygen 2p-states to the bottom of the conduction band formed by hybridization of oxygen 2p-states and gallium 4s-states. The single-oscillator approximation parameters, dispersion energy, degree of ionic chemical bonding, and coordination number were found for fi lms with normal dispersion.Keywords: thin fi lm, gallium oxide, refractive index, dispersion.Introduction. Single-and multi-layered fi lms are used to manufacture optical light fi lters and to coat optical components. Recently, thin fi lms of β-Ga 2 O 3 have been widely used. Pure or doped β-Ga 2 O 3 fi lms are used as transparent electrodes for developing gas sensors [1, 2], photoluminophores [3][4][5], and cathodoluminophores or electroluminophores [6-8] depending on the preparation method and dopants. The properties of UV detectors [9] and gas sensors [10-12] based on β-Ga 2 O 3 fi lms that were designed to convert solar energy and to detect in the atmosphere reducing and oxidizing gases, including low concentrations of oxygen [12], were reported. Although the optical properties of thin fi lms were investigated earlier [1,2,9,13,14], the dispersion properties and their relationship to the energy structure and crystal properties were not studied in detail. The study of these properties is rather critical. The refractive index determines the refl ectivity of the fi lms; the dispersion properties, its spectral distribution during fabrication of optical light fi lters or coating of optical components. This prompted the present investigation.Experimental. Ga 2 O 3 thin fi lms (0.2-0.8 μm) were prepared by radiofrequency (RF) ion-plasma sputtering on v-SiO 2 fused quartz substrates. The RF-sputtering used a magnetic fi eld of external solenoids for compression and additional ionization of the plasma column. Deposited fi lms were heat treated in oxygen or Ar at 1000-1100°C and in H 2 at 600-650°C. X-ray powder patterns showed that the fi lms were polycrystalline and differed depending on the heat treatment method. Figure 1 shows characteristic diffraction patterns for the obtained fi lms. The results indicated that the fi lms were oriented in the (400), (002), (111), and (512) planes after annealing in oxygen. Films oriented in the (400), (002), (111), and (512) planes also dominated after annealing in Ar. However, the relative orientation in the (400) plane decreased whereas those in the (111) and (113) planes increased. Films annealed in H 2 showed a weakly developed structure in which refl ections from the (400), (002), and (512) planes also dominated. Refl ections that did not correspond to Ga 2 O 3 were not identifi ed in the dif...
