Structure and optical properties of thin Al$_2$O$_3$ films deposited by the reactive ion-plasma sputtering method on GaAs (100) substrates

Structural analysis and optical spectroscopy are used to study the properties of ultrathin Al$_2$O$_3$ films deposited in an ion-plasma sputtering installation. It is possible to demonstrate that the technological method used to deposit the films can yield amorphous, smooth, pore-free, and almost homogeneous films in which crystals of the $\alpha$ phase of aluminum oxide Al$_2$O$_3$ nucleate. The films transmit light extremely well in the IR (infrared), visible, and UV spectral ranges and are of potential importance for the development on their basis of antireflection coatings for mirrors of high-power semiconductor lasers based on III–V compounds.