Wurtzite zinc-based oxynitrides as promising photovoltaic absorbers: epitaxy, band-structure engineering and heterostructures
Synthesis and Properties of Functional Materials
Final Report Abstract
Band bowing of wurtzite zinc-based oxynitrides based on (GaN)1−x(ZnO)x and (AlN)1-x(ZnO)x solid solutions has been experimentally demonstrated for the first time, which allows a strong visible-light absorption by combing wide-bandgap ZnO and III-nitrides. We have succeeded in producing epitaxial and continuous composition spread thin films of Zn-based oxynitrides by plasma-enhanced or traditional pulsed laser deposition. Strong optical absorption has been observed for both (GaN)1−x(ZnO)x and (AlN)1-x(ZnO)x solid solutions with large absorption coefficient α on the order of 10^4 cm^−1 in the visiblelight region. According to the absorption spectra, the lowest bandgap value of the wurtzite zinc-based oxynitrides could be as low as 2.0 eV (or even lower) depending on the composition. Beyond the tasks of this project, we have also conducted theoretical studies on the fundamental band structures of both (GaN)1−x(ZnO)x and (AlN)1-x(ZnO)x solid solutions, which agreed well with our experimental findings. These results prove that (GaN)1−x(ZnO)x and (AlN)1-x(ZnO)x solid solutions are promising non-toxic photovoltaic absorbers for sustainable energy technologies. Thus, the main goals of the project have been met. For further investigations on the solar cell devices, we have already achieved the fabrication of highquality CuI thin films, which will be an ideal p-type partner material to construct heterojunctions with Zn-based oxynitrides. This device study will be continued in the near future, partially supported by the funding of Dr. Chang Yang at his new position in China.
Publications
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Epitaxy of (GaN)1-x(ZnO)x Solid-Solution Thin Films with Widely Tunable Chemical Composition and Strong Visible Absorption, Physical Review Applied, 2018, 10, 044001
C. Yang, Y. Hirose, N. Kashiwa, and T. Hasegawa
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Controllable growth of copper iodide for high-mobility thin films and self-assembled microcrystals, ACS Applied Electronic Materials, 2020, 2, 3627
C. Yang, E. Rose, W. Yu, T. Stralka, F. Geng, M. Lorenz, M. Grundmann
