Modification of optical and electrical properties in sputtered CsI films by dopant incorporation

Abstract This study investigates the effects of alkaline-earth dopant inclusion on the optical and electrical properties of sputtered cesium iodide (CsI) thin films for potential radiation-sensing applications. CsI layers deposited on Si(100) substrates at sputtering powers of 30 W and 50 W were co-doped with Sr,Tl and characterized using GI-XRD, UV–Vis spectroscopy, Hall-effect measurements, and I–V analysis, complemented by computational modeling and α-particle response simulations. Structurally, Sr,Tl incorporation results in modest lattice relaxation of − 2% strain without symmetry degradation, indicating that residual strain remains dominated by growth conditions. Optical measurements reveal a dopant-related transition near 2.5 eV and an intrinsic near-edge transition around 4.1–4.2 eV, associated with defect-modified electronic states. Hall-effect measurements confirm p-type conductivity with a carrier density of 8.49 E + 09 cm⁻ 3 , mobility of 30.5 cm 2 V⁻ 1 s⁻ 1 , and resistivity of 5.74 E + 05 Ω·cm. The CsI:Sr,Tl/Si heterojunction exhibits stable rectifying I–V behavior (Vₒₙ = + 5.4 V, V BR = − 5.4 V) and internal electric fields on the order of 10 4 –10 5 V cm⁻ 1 , while transient-response simulations indicate fast, drift-dominated charge collection with energy-proportional currents. These results demonstrate that Sr,Tl co-doping, combined with controlled thin-film growth, enables microstructural and defect regulation that supports electrically robust CsI-based heterojunction devices, reinforcing the potential of lead-free, wide-bandgap CsI thin films for radiation-detection applications.