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

Zn1-xMgxO (x less than or equal to 0.21) thin films were prepared on (0001) -oriented sapphire (Al2O3) Substrates by rf magnetron sputtering. The obtai ned films are well oriented to (0001) with their crystalline quality improv ing with increasing substrate temperature in the 200-500 degrees C range. T he Mg composition of the films increases with increasing substrate temperat ure. The pseudodielectric functions of the films measured at room temperatu re by spectroscopic ellipsometry show that the fundamental absorption edge of Zn1-xMgxO shifts to higher energies with increasing Mg composition. Desp ite the alloying disorder, the optical spectra of the alloys exhibit strong excitonic contribution to the fundamental band-gap transition as in pure Z nO. The blue-shift of the fundamental band gap of the x = 0.21 alloy from t hat of ZnO is estimated to be 400 meV. (C) 2000 Elsevier Science Ltd. All r ights reserved.