Facile Synthesis of Well-Aligned ZnO Nanowires on Various Substrates by MOCVD for Enhanced Photoelectrochemical Water-Splitting Performance

We present results related to the growth of high-aspect-ratio ZnO nanowires (NWs) using metal-organic chemical vapor deposition based on the study of the NW growth mechanism on various substrates. The ZnO NWs on Si, sapphire, and GaN substrates were optically and structurally characterized, and the effect of a low-temperature ZnO buffer layer was investigated. It was demonstrated that NWs deposited under the same conditions could be randomly oriented or vertically aligned. Well-aligned ZnO NWs were grown on Si (100) substrates with a ZnO buffer layer which was grown via atomic layer deposition. The NWs are single crystalline wurtzite structures with a preferential growth in the (002) direction. Room-temperature photoluminescence measurements exhibited a strong ultraviolet emission and suppressed visible emission. This result affirms the absence of defects related to ZnO or oxygen vacancies. On changing the substrate, different morphologies of the ZnO NWs can be attained, which present different photoelectrochemical (PEC) performances. Among these, ZnO NWs grown on GaN and Si substrate (with a buffer layer) exhibited a superior photocurrent of 4.75 and 3.24 mA cm(-2) at 1.5 V (vs Ag/AgCl), respectively. This excellent PEC performance can be attributed to the enhancement of light absorption intensity and the increased photogenerated carrier lifetime, implying that well-aligned ZnO NWs are suitable for PEC water splitting.