Nanocomposites and nanomaterials

Surface morphology and X-ray luminescent properties of 
β-Ga2O3 thin films
Bordun O. M. 1, Bordun B. O. 1, Medvid I. I1
1 Ivan Franko National University of Lviv 50, Drahomanov Str., UA-79005 Lviv, Ukraine. 
E-mail: oleh.bordun@lnu.edu.ua

Thin films of β-Ga2O3 with a thickness of 0.2–0.8 μm were obtained by RF ion-plasma sputtering in argon atmosphere. X-ray diffraction studies showed the presence of a polycrystalline structure with a predominant orientation in the (400), (002), (111) and (512) planes.
Investigation of the surface morphology of thin films by atomic force microscopy (AFM) shows that, during thermal treatment, the mean size of nanocrystalline grains from which form films increases. According to AFM data, it is shown that, the presence of thermal treatment in an argon atmosphere leads to an increase in the mean diameters of nanocrystalline grains from 19.6 to 67.2 nm. Based on the analysis of grain size diameter distribution results, it was found that regardless of the presence of thermal treatment, the three modal distribution, which is formed during deposition of β-Ga2O3 thin films by RF sputtering is observed. The presence of thermal treatment does not change the shape of this distribution but leads to a uniform increase in grain size along the entire distribution.
Investigation of the X-ray luminescent properties of these films show that in the temperature range of 80 to 300 K in thin films of -Ga2O3 there is X-ray luminescence, the maximum of the spectrum of which with increasing temperature from 80 to 300 K shifts from 395 nm to 425 nm. This spectrum in the investigated temperature range using the linear electron-phonon coupling model  was simulated by the superposition of two independent Gaussians with maxima at 3.14 and 2.95 eV. The temperature dependence of the X-ray luminescence intensity of the selected bands indicates the associative nature of the centers responsible for these bands. These centers are associated with the associative acceptor complex (VOVGa)'. The complex consists of a doubly charged oxygen vacancy VO** and a triple-charged vacancy of VGa'''.