The band structure of ALCVD AlZr- and AlHf-oxides as measured by XPS

This paper investigates the effect of thickness, composition and anneal temperature in N2 on the band gap of the mixed oxide layer and the band offset with the Si substrate for layers grown by atomic layer deposition. For 1:1 (Al/Zr or Al/Hf) mixed oxides, the band gap reaches the bulk value for a thickness larger than 2 nm. In both cases (AlxZryOz and AlxHfyOz), the bulk values of the band gap show a linear dependence on the Al2O3 mol%, going from 5.6 (5) eV for pure ZrO2 (HfO2) to 6.7 eV for pure Al2O3. The effect of a post-deposition anneal on the band gap and the valence band alignment is also studied. Here, AlxHfyOz and AlxZryOz seem to act differently: while the annealing temperature does not have any influence on the band gap of AlxZryOz mixed oxide, the annealing in N2 at temperature from 900 °C generates an increase in the band gap value measured by XPS for AlxHfyOz.