Photoconductivities in m-plane and c-plane ZnO epitaxial films grown by chemical vapor deposition on LiGaO2 substrates: a comparative study

The photoconduction properties of (non-polar) m-plane and (polar) c-plane ZnO thin films epitaxially grown on relatively lattice-matched LiGaO2 substrates by chemical vapor deposition have been investigated and compared. Structural and photoluminescence characterizations indicate that the c-plane ZnO films possess higher crystallinity than the m-plane ZnO films. Owing to their superior crystallinity and lower dark current, the c-plane ZnO films exhibit significantly higher optimal sensitivity (S = 4650) to ultraviolet light than the m-plane ZnO films (S = 10). However, in terms of photocurrent generation efficiency, the m-plane ZnO films exhibit over one order of magnitude higher responsivity (R = 0.05–3.2 A W−1) than the c-plane ZnO films (R = 0.009–0.035 A W−1) in the light intensity range 1.6–320 W m−2. The probable mechanisms causing the aforementioned differences based on surface-dominant photoconduction and bulk-dominant structural and photoluminescence properties are also discussed.