Semiconductors group

Abstract:

New compounds are discovered in the under-explored d 10 –s 2 (Cu–Sn) family using exploratory synthesis guided by computational tools. Band-gaps in the visible region with moderate charge-carrier mobilities make these potential solar absorbers. We explore multiple-cation chalco–halide phase fields evaluated by their synthetic accessibility using machine learning models. Exploratory synthesis guided by computational tools leads to the discovery of two new compounds; CuSn 2 SI 3 and Cu 0.35 Sn 5.29 S 2 I 7 , their structures, and electronic and optical properties are reported herein. This is the first report of a stable quaternary compound in the Cu–Sn–S–I phase field. The two new compounds show related crystal structures where Sn 4 S 2 I 4 layers are a common structural motif in both. These Sn 4 S 2 I 4 layers are connected by Cu 2 I 2 layers and disordered Cu–Sn–I layers, forming the three-dimensional structures of CuSn 2 SI 3 and Cu 0.35 Sn 5.29 S 2 I 7 respectively. Electronic band structure calculations using density functional theory show the presence of a direct band gap in CuSn 2 SI 3 and suggest anisotropic transport, in line with the layered structure of the compound. A mixture of the two compounds with ∼86% CuSn 2 SI 3 , shows a band gap in the visible region, close to 2.1 eV and a significant photo-induced charge carrier mobility of ∼1.3 cm 2 V −1 s −1 . This demonstrates Cu–Sn chalco–halides can form a promising phase space to explore for solar absorber materials, with further design and tuning of band gap.

Abstract:

Thermo-optical nonlinearities (TONL) in metasurfaces enable dynamic control of optical properties—such as transmitted power, phase, and polarization—through external stimuli like laser irradiation or temperature. Due to the inherently slow thermal dynamics of extended systems, research has primarily focused on steady-state effects, as rapid modulation is typically considered challenging. In this study, photo-driven TONL is investigated in amorphous silicon (a-Si) metasurfaces under both steady-state and, more importantly, dynamic conditions using a modulated 488 nm continuous-wave pump laser. First, a non-monotonic change is observed in transmission as a function of irradiation intensity at a wavelength red-shifted by 15 nm from the electric-dipole resonance. Specifically, transmission initially decreases by 30% before increasing by 30% as the laser intensity reaches 5 mW/ (Formula presented.). Next, it is demonstrated that TONL decouple thermal and optical response times, with the optical response being up to seven times faster than the thermal response under tested conditions ((Formula presented.) (Formula presented.) vs. (Formula presented.) (Formula presented.)). Most remarkably, it is experimentally shown that the interplay of these effects enables optical modulation at twice (100 kHz) the excitation laser's modulation frequency (50 kHz). Finally, it is shown that exploiting these unique conditions allow thermo-optical metasurfaces to intrinsically encode multiple optical states within a single modulation cycle, realizing a self-modulating photonic platform. TONL thus open new avenues for engineering active metasurfaces that combine fast, high-amplitude modulation with self-modulating optical dynamics, making them promising for next-generation optical switching, dynamic holography, optical information processing, and neuromorphic computing.