Electron beam irradiation modulated vacancy point defect structure transformation in zinc germanium diphosphide crystals

Due to the powerful ionization and displacement effect, electron beam irradiation technology has been widely employed to modulate the defect structures of various crystalline materials, thereby improving their application performance. In zinc germanium diphosphide (ZnGeP₂) crystal, the vacancy defects would lead to noxious optical absorption at the pumping range, which severely limits the efficiency of mid-infrared laser output. Herein, electron beam irradiation treatment is used to improve the optical transmittance, and the mechanism of the defect structure transformation is clarified. The singly ionized zinc vacancies (V_Zn⁻) almost disappear, and the neutral phosphorus vacancies (V_P⁰) emerge after electron beam irradiation while the ZnGeP₂ crystal structure remains unchanged. The Hall effect measurement and first-principles calculation further indicate that electron irradiation would generate more electron-hole pairs and increase the hole carrier concentration in p-type ZnGeP₂, which will further convert V_Zn⁻ to doubly ionized zinc vacancies (V_Zn²⁻) and singly ionized phosphorus vacancies (V_P⁺) to V_P⁰). These findings confirmed that the overall optical performance improvement of ZnGeP₂ crystal is attributed to ionization effect related vacancy defect structure transformation rather than atomic displacement effects induced new vacancy defects. This work demonstrates an efficient strategy to modulate the vacancy defect structure and promote future electron beam irradiation research for functional crystals.