Spectroscopic ellipsometry study of Zn1−xMgxO thin films deposited on Al2O3(0001)

Zn1−xMgxO (x≤0.21) thin films were prepared on (0001)-oriented sapphire (Al2O3) substrates by rf magnetron sputtering. The obtained films are well oriented to (0001) with their crystalline quality improving with increasing substrate temperature in the 200–500°C range. The Mg composition of the films increases with increasing substrate temperature. The pseudodielectric functions of the films measured at room temperature by spectroscopic ellipsometry show that the fundamental absorption edge of Zn1−xMgxO shifts to higher energies with increasing Mg composition. Despite the alloying disorder, the optical spectra of the alloys exhibit strong excitonic contribution to the fundamental band-gap transition as in pure ZnO. The blue-shift of the fundamental band gap of the x=0.21 alloy from that of ZnO is estimated to be 400 meV.