Effect of deposition conditions and composition on band offsets in atomic layer deposited HfxSi1−xOy on InGaZnO4

HfO2 or HfxSi1−xO4 (consisting of HfO2/SiO2 multilayers) were deposited at 200 °C by atomic layer deposition (ALD) onto a-InGaZnO4 (IGZO) layers deposited by sputtering at room temperature and the band offsets in the HfxSi1−xOy/InGaZnO4 heterostructures determined by x-ray photoelectron spectroscopy. The values for HfxSi1−xOy/IGZO are different from those obtained when sputtering is used to deposit the dielectric, indicating that surface disordering or metal inclusions can play a role in the offsets. Similarly, the band offsets for SiO2 deposited on IGZO by ALD are larger than previous reports for the same system in which the SiO2 was deposited by plasma enhanced chemical vapor deposition. In that latter case, the effect of incorporated hydrogen in the SiO2 may play a role by reducing the bandgap. By contrast, there was no difference in the offsets in interfaces initiated with SiO2-first versus HfO2-first deposition and no effect of annealing the IGZO at the ALD-deposition temperature prior to dielectric deposition. The valence band offset for HfxSi1−xOy/IGZO was determined as a function of composition, with values ranging from 1.73 eV for pure SiO2 to 0.52 eV for pure HfO2. Across the entire composition range, the HfxSi1−xOy/InGaZnO4 system has a nested, or straddling, gap (type I) alignment.