Periodic Reporting for period 2 - SECANS (Solar-to-Chemical Energy Conversion with Advanced Nitride Semiconductors)
Período documentado: 2022-01-01 hasta 2023-06-30
In a second publication, we turned to the more commonly explored nitrogen-rich phase of Ta3N5 and investigated the impact of substitutional oxygen impurities on its optoelectronic and photoelectrochemical characteristics. Using our reactive sputtering approach combined with ammonia annealing, we were able to generate some of the lowest oxygen content films reported to date, which enabled fundamental studies of the semiconducting properties of this compound. Our results enabled a resolution to a long-standing uncertainty regarding the nature of the fundamental bandgap, indicating conclusively that it is indirect. The commonly-observed photoluminescence from the material is disorder-activated and can be suppressed in films possessing high compositional purity and structural quality. The photoelectrochemical performance of resulting Ta3N5 photoelectrodes could be understood in terms of the characteristics of native and impurity defects.
Considering the propensity of nitride surfaces to oxidize under photoelectrochemical conditions, we have developed atomic layer deposition processes for formation of phase-tunable water oxidation catalysts, which resulted in a third publication. Ongoing work is devoted to applying these materials to nitride photoanode surfaces and to studying photocarrier and reaction dynamics on their surfaces.
Though still in progress, studies of Zr- and Zn-based nitrides have provided additional new insights into the role of oxygen on stabilizing different phases of material, affecting the electronic transport characteristics, and defining the interfacial reactivity for energy conversion. Overall, the compact morphology, low defect content, and high optoelectronic quality of these films provide a basis for further optimization of photoanodes and may open up further application opportunities beyond photoelectrochemical energy conversion.