Band alignment engineering: ultrabroadband photodetection with SnX₂ (X  =  S, Se)/ZnS heterostructures

Ultrabroadband mid-frequency infrared photodetectors have important applications in surveillance, medical diagnosis, bioimaging and navigation aids. Thus, researchers hope to detect mid-infrared radiation with larger wavelength. However, due to the limitation of room temperature, it is difficult for these detectors to detect mid-infrared with 4 µm or larger wavelength. Therefore, at room temperature, how to realize mid-infrared detection in a wide range has become an urgent problem to be solved. In this paper, the band structure of SnX₂ (X  =  S,Se)/ZnS and SnS_2(1−ŋ)Se_2ŋ /ZnS was studied by the density functional theory based first-principles methods. Under the specific stacking procedure, changing the of SnS_2(1−ŋ)Se_2ŋ, the band gap of heterojunctions can be continuously tuned from 0 to 0.97 eV. Amazingly, the band structure maintains the characteristics of a type-II heterojunction. The photodetection in our work is estimated for wavelengths from 1.2 µm to 10 µm, covering a wide wavelength range of mid-infrared. Such a wide range is considerable in current research. The characteristics of type-II band structure and the wide detection range imply that SnX₂ /ZnS has great potential in mid-frequency infrared detection. Our work may provide some breakthroughs for the research of multiband photodetectors at room temperature. (paper)