离子注入对ZnTe:O中间带光伏材料的微观结构及光学特性的影响

II-VI和III-V族高失配合金半导体是新型高效中间带太阳电池的优选材料体系,但中间带的形成及其能带调控等关键问题仍未得到有效解决.采用氧离子注入方式,在非平衡条件下对碲化锌(Zn Te)单晶材料实现了等电子掺杂,深入研究了离子注入对Zn Te:O材料的微观结构和光学特性的影响.研究表明:注入合适浓度的氧离子(2.5×1018cm-3)将会形成晶格应变,并诱导1.80 e V(导带下0.45 e V)中间带的产生;而较高浓度(2.5×1020cm-3)的氧离子会导致Zn Te注入层表面非晶化,并增强与锌空位相关的深能级(～1.6 e V)发光.时间分辨光致发光结果显示,离子注入诱导形成的中间带主要是和氧等电子陷阱束缚的局域激子发光有关,载流子衰减寿命较长(129 ps).因此,需要降低晶格紊乱度和合金无序,实现电子局域态向扩展态的转变,从而有效调控中间带能带结构.

Effect of oxygen implantation on microstructural and optical properties of ZnTe:O intermediate-band photovoltaic materials

Group Ⅱ-VI and Ⅲ-V highly mismatched alloys are promising material systems in the application of high efficiency intermediate-band solar cell (IBSC), however, the key issues including band engineering of intermediate band still remain challenging. In this study, ZnTe:O alloys have been produced by isoelectric oxygen implantation into ZnTe single crystal, and the influences of implantation on the microstructural and optical properties of ZnTe:O have been investigated in detail. It is found that a proper dose of oxygen ions can lead to a compressive strain in the lattice and induce the formation of intermediate band located on the energy level of ～ 0.45 eV below the conduction band. While a high dose of oxygen ions causes ZnTe surface layer to become amorphous and enhances the deep level emission around 1.6 eV, which is related to Zn vacancies. Results of resonant Raman and time-resolved photoluminescence spectra indicate that implantation induced intermediate band is related to the localized exciton emission bound to oxygen isoelectric trap, and the associated photo excited carriers have a relatively long decay time. This suggests that the reduction of lattice distortion and alloy disorder may be needed for converting localized states of the intermediate band into extended states, which is crucial to realize high efficiency ZnTe:O based IBSCs.
Keywords： intermediate band ion implantation highly mismatched alloys group Ⅱ-VI semiconductors