Photovoltaic effect in metal foils and crystals of topological insulators

Abstract

We report that the photovoltaic effect can be produced in metals, semimetals, and semiconductor 3D topological insulators with crystalline and nanostructured states. The behavior of charge carriers in topological insulator crystals and metal foils was investigated under laser illumination. We developed a method for the measurement of electrical potential difference on surfaces of three-dimensional topological insulators: Bi and Sb single crystals, Bi foils, and (Bi_1−xSb_x)₂Te₃ and (Bi_1−xSe_x)₂Te₃ nanostructured crystals, as well as metal foils of Al and Ni alloys. The surface voltage depends on the properties of samples obtained by different methods. The value of the surface potential difference depends on the laser illumination of the top or bottom surfaces of the samples. A negative surface potential difference was observed in most samples, except for Al foils and Ni alloy foils, with top surface illumination. Laser illumination of the bottom surface caused a larger surface potential difference in topological insulators, with the opposite polarity. Surface structure defects and specific band structures in the topological insulators studied provided an increase in the electrical potential difference on their surface due to the photovoltaic effect. The reduction of deposited laser energy from the bottom surface to the top surface by a factor of 1000 due to the low thermal conductivity of topological insulators increased the electrical potential difference by factors of 1.8–3.8. These results promise a new possibility for prospective research and development of energy-efficient photonic devices.