An indirect-to-direct band gap transition of NaSbS2 via minor Ga doping: A theoretical study

The efficiency of NaSbS2 is limited by its wide indirect band gap. Alloying is a very effective strategy to tune the band gap over a wide range for the mixed-anion NaSb(S,Se)2 alloys. However, these compounds are still indirect band gap semiconductors. The influence of Ga doping on the structure, electronic, and optical properties of NaSbS2 is studied for the first time. Our calculated results show that NaSbS2 is an indirect band gap semiconductor, and the difference between the indirect and direct band gaps is less than 0.1 eV. Moreover, the forbidden transition is discovered for the fundamental direct bandgap of NaSbS2. The results indicate that the NaSb1-xGaxS2 alloys are predicted to be synthesized in the proper conditions. An indirect-to-direct band gap transition is observed from NaSbS2 to NaSb1-xGaxS2. The minor Ga doping (less than10 %) has little effect on the electronic and optical properties of NaSbS2. Importantly, the weak transition of the fundamental direct bandgap is allowed for NaSb1-xGaxS2. This study can provide a route to explore the high efficiency of novel based-NaSbS2 materials.