Thermoreflectance characterization of band-edge excitonic transitions in CuAlS2 ultraviolet solar-cell material

Near band edge transitions of CuAlS2 chalcopyrite crystals have been characterized using temperature-dependent thermoreflectance (TR) spectroscopy in the temperature range between 30 and 340 K. A lot of interband transition features of EAn=2, EAn=3, EBn=2, EC, ED, EE, and EF were detected in the low-temperature TR spectrum of 3–6 eV at 30 K. Transition energies of the TR features of CuAlS2 are analyzed. Transition origins of the features are evaluated. Optical-electric conversion behavior of CuAlS2 was evaluated by photoconductivity (PC) measurement at 300 K. The PC spectrum reveals that the maximum photoresponse occurs near the energy positions of EAn=2, EAn=3, and EBn=2 features. The features are the fundamental band edge excitons which dominate photoelectric conversion behavior of CuAlS2 ultraviolet solar-energy material.

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