Abstract: Band bending and built-in electric fields at semiconductor heterojunction interfaces are fundamental to photoelectric and photochemical energy conversion, serving as key teaching points in advanced undergraduate courses that integrate band theory, interface electric fields, and carrier dynamics. This study designs a physical chemistry experiment for senior undergraduates: NiO thin films are fabricated on high-resistance n-type Si substrates via spin-coating and annealing to construct NiO/Si heterojunctions, followed by non-contact in situ measurements of terahertz transmission changes induced by photoconductivity using terahertz time-domain spectroscopy (THz-TDS) under 532 nm continuous-wave illumination. Control groups including bare sapphire (C₀), NiO/sapphire (C₁), bare Si(S₀), and NiO/Si(S₁) are established, alongside process variables such as annealing temperature and film thickness, to form a closed-loop evidence chain linking fabrication processes, interface properties, carrier dynamics, and spectroscopic signals. Results demonstrate that S₁ exhibits significantly greater terahertz modulation depth than S₀ under identical pumping conditions, while C₁ shows negligible response, indicating that interfacial effects substantially enhance the steady-state photoconductivity of Si. This phenomenon aligns with band bending-induced carrier separation/accumulation at heterojunctions, providing indirect spectroscopic evidence and a quantitative teaching metric for “inferring band bending from photoconductivity enhancement”. The experiment integrates thin-film fabrication, semiconductor band theory, and terahertz spectroscopic data analysis, training students in hands-on skills, data interpretation, and controlled experimental reasoning.

Key words: Physical chemistry experiment, Band bending, Heterojunction, Terahertz time-domain spectroscopy