Engineering a Correlated Narrow‐Gap Semiconductor: Effects of Ga Substitution in EuZn ₂ P ₂

The effect of Ga substitution on the electronic, magnetic, and low‐energy responses of the Zintl phase is investigated by electrical transport, electron spin resonance (ESR), and terahertz time‐domain spectroscopy (THz‐TDS). Incorporating Ga into () reduces the electrical resistivity, indicating enhanced free‐carrier density and a narrowed semiconducting gap. ESR confirms the persistence of moments while showing a crossover from a Lorentzian to a Dysonian lineshape, consistent with reduced skin depth, increased carrier density, and the emergence of diffusive contributions. The Ga‐substituted compound displays pronounced negative magnetoresistance linked to magnetic‐polaron formation. THz‐TDS reveals strong low‐frequency absorption and a notable enhancement of the Drude conductivity in the substituted material, together with an increased carrier scattering time and enhanced carrier‐density–to–effective‐mass ratio. These results demonstrate that Ga substitution tunes charge transport, carrier dynamics, and short‐range magnetic correlations in , establishing as a promising platform for engineering correlated narrow‐gap magnetic semiconductors with enhanced electronic and spin‐dependent functionalities.