A GaN/HfZrCO₂ heterojunction with excellent photoresponse and superior hydrogen evolution reaction performance

In this work, first-principles calculations are employed to investigate GaN/HfZrCO₂ heterostructures in terms of structural stability, electronic properties, optoelectronic behavior, and mechanical characteristics. Monolayer GaN and HfZrCO₂ are indirect semiconductors with bandgaps of 3.20 eV and 1.73 eV, respectively, while their heterostructure exhibits a reduced type-II indirect bandgap of 1.673 eV, enabling an extended spectral response and efficient separation of photogenerated carriers. Work-function and charge-distribution analyses reveal an intrinsic interfacial electric field directed from GaN to HfZrCO₂. Under biaxial strain from -8% to +8%, the heterostructure shows pronounced bandgap modulation under compression but remains strain-insensitive under tension. For the hydrogen evolution reaction, hydrogen adsorption on the N site yields the most favorable configuration with a low overpotential of 0.27 V, indicating excellent catalytic activity. The heterostructure also exhibits strong broadband light absorption with a maximum absorption coefficient of 5.89 × 10⁵ cm^-1. Overall, GaN/HfZrCO₂ demonstrates significant potential for future energy applications and next-generation optoelectronic devices.