Elimination of band-edge states by Frenkel-like defects: Application in inorganic compound α-Ag2S

The elimination of impurity states is an effective method to improve the properties of semiconductor material. Interstitial Se or Te doping in inorganic compound α-Ag₂S would induce highly localized impurity states around the valence band maximum (VBM), which are so-called perturbed host states (PHSs). These PHSs possibly act as the recombination center and would affect the carrier transport. Herein, we propose the self-compensation method to eliminate the PHSs by introducing Frenkel-like defects. The first-principles calculations prove that the Frenkel-like defects, i.e., one first-nearest neighbor S-vacancy (V_1S) around the interstitial dopant (Se_i + V_1S or Te_i + V_1S), are able to eliminate the PHSs. The Frenkel-like defect can not only achieve compensation for electronic structure, but also achieve compensation for carrier concentration. Instead, excessive Schottky defects would lead to partial compensation or overcompensation. Additionally, it is also found that the existence of Frenkel-like defect can lower the formation energy and improve the stability of the system. This discovery highlights the importance of Frenkel-like defects in eliminating impurity states, which is fundamentally different from the traditional scheme that mainly credits no introduction of additional foreign elements. Our results provide a new avenue to the design of eliminating impurity states in other semiconductors.