Abstract Zn diffusion processes in n-Ga0.78In0.22As0.2Sb0.8 epitaxial films are studied using different diffusion sources, a series of the Zn profiles with single and double humps are obtained. The group V-atoms (As and Sb) are found to have little effect on suppressing the surface “dead region”. The Ga and In atoms have entirely different effect on diffusion although they are both group III-atoms. The “dead region” is suppressed completely under Ga-rich conditions, while the suppression will not occur under In-rich conditions. The GaInAsSb cells are fabricated under pure Zn and Ga-rich conditions. An electrical heating thermophotovoltaic system is fabricated for cell testing. Under the radiation from 1055 °C-SiN ceramics emitter, the output power density of the GaInAsSb cell obtained under Ga-rich condition is much larger than that of the cell obtained under pure Zn condition, which demonstrated that the GaInAsSb cells can be fabricated without precise etching under Ga-rich conditions.