Circular photogalvanic effect in large-scale tellurium thin films

Combining the advantages of exotic topological physics and versatile semiconducting properties, elemental tellurium (Te) has attracted renewed interest in recent years. Both bulk and two -dimensional Te have been extensively studied for their optical activity and the unique spin texture in reciprocal space [1, 2]. The Te band structure is characterized by strong spin- orbit interactions and anisotropic effects, leading to the formation of multiple Weyl cones in different points of the Brillouin zone. Recently, Powder Vapor Deposition (PVD) has emerged as a scalable and reliable method to produce high-quality Te thin films. By tuning substrate temperature and growth time, film thickness and morphology can be precisely controlled, enabling manipulation of the electronic properties typical of low dimensional structures [3]. Helicity resolved photocurrents resulting from different physical processes are experimentally measurable and provide a direct probe for studying band geometry in topological materials [4]. In this work, we investigate circular polarisation-dependent photocurrents in PVD-grown Te thin films of varying thicknesses. Surface morphology and grain dimensions were characterized using atomic force microscopy (AFM) and Raman spectroscopy. Excellent stability, with no degradation under ambient conditions, was ensured by the introduction of an optically transparent alumina top layer immediately after Te deposition. Our zero-bias measurements reveal distinct mechanisms for photocurrent generation. By performing angle-of-incidence and laser-power-dependent experiments across the visible to mid-infrared spectral range, we isolated the contribution of the circular photogalvanic effect (CPGE) from other polarisation-independent effects. Remarkably, the CPGE-related component, given the polycrystalline nature of the films, can be observed even in the absence of preferential Te crystalline orientation. These findings suggest the robustness of Te topological properties with respect to the growth method and its potential for helicity-sensitive optoelectronic applications. Furthermore, the scalability of PVD techniques highlights the feasibility of integrating Te into next-generation devices with novel chiral functionalities. References: [1] Ma J., et al. "Unveiling Weyl-related optical responses in semiconducting tellurium by mid- infrared circular photogalvanic effect." Nature Communications 13.1 (2022): 5425. [2] Niu C., et al. "Tunable chirality-dependent nonlinear electrical responses in 2d tellurium." Nano letters 23.18 (2023): 8445-8453. [3] McIver J. W., et al. "Control over topological insulator photocurrents with light polarization." Nature nanotechnology 7.2 (2012): 96-100. [4] Ghomi S., et al. "Tailoring the dimensionality of tellurium nanostructures via vapor transport growth." Materials Science in Semiconductor Processing 168 (2023): 107838.