Real time spectroellipsometry study of the interaction of hydrogen with ZnO during ZnO/a-Si1−xCxH interface formation

Using real time spectroellipsometry (SE), we have studied the interfacial interactions that occur when i- and p-type hydrogenated amorphous silicon-carbon alloys (a-Si1−xCx:H) are deposited from hydride-containing plasmas onto transparent, conducting films of ZnO. The SE spectra collected during the nucleation of a-Si1−xCx:H onto ZnO reveal a widening of the near-interface optical gap of ZnO by ∼0.1 eV, an effect attributed to the penetration of atomic H from the plasma. The SE data, along with ex situ secondary ion mass spectrometry, reveal that the H diffuses into ZnO to depths ≳200 Å. The defects that result from H incorporation in ZnO (e.g., O vacancies) lead to a shift in the near-interface Fermi level higher into the ZnO conduction band and to an estimated enhancement in the electron concentration by ∼1020 cm−3.