Due to the wide spectral absorption and ultrafast electron dynamical response under optical excitation, topological insulator (TI) was proposed to have appealing application in next-generation photonic and optoelectronic devices. Whereas, the bandgap-free speciality of Dirac surface states usually leads to a quick relaxation of photoexcited carriers, making the transient excitons difficult to manipulate in isolated TIs. Growth of TI Bi2Te3/Ge heterostructures can promote the specific lifetime and quantity of long-lived excitons, offering the possibility of designing original near-infrared optoelectronic devices, however, the construction of TI Bi2Te3/Ge heterostructures has yet to be investigated. Herein, the high-quality Bi2Te3/Ge heterojunction with clear interface was prepared by PVD strategy. A significant photoluminescence quenching behaviour was observed by experiments, which was attributed to the spontaneous excitation transfer of electrons at heterointerface via theoretical analysis. Then, a self-powered heterostructure photodetector was fabricated, which demonstrated a maximal detectivity of 1.3×1011 Jones, an optical responsivity of 0.97AW-1, and ultrafast photoresponse speed (12.1 μs) under 1064 nm light illumination. This study offers a fundamental understanding of the spontaneous interfacial exciton transfer of TI-based heterostructures, and the as-fabricated photodetectors with excellent performance provided an important step to meet the increasing demand for novel optoelectronic applications in the future.

To date, the pure-phase SnSe films and nanostructures have been experimentally prepared by means of chemical vapor deposition, mechanical exfoliation, onestep solvothermal method, hot-injection method, and so on. [5][6][7] It was also confirmed that by using of different growth technics or conditions, the SnSe crystals with different phases can be realized. [8][9][10] It turned out that the SnSe crystal with cubic rock-salt structure should belong to the prototypical 3D topological crystalline insulator (TCI) phase. [11][12][13] While, for the SnSe crystal with orthorhombic structure, it was identified as the typical 2D layered semiconductor. Its two adjacent diatomic layers bind together by weak van der Waals interaction, which is similar to other transition-metal-dichalcogenide semiconductors such as MoS 2 and WSe 2 . [14][15][16][17][18] Consequently, benefiting from the existence of Dirac surface state on TCI phase SnSe crystal, it is advantageous to realize the predominated transport of surface carriers with no backscattering and higher mobility. [19][20][21][22] Whereas, for the SnSe crystal with orthorhombic lattice structure, it is favorable for the layer-by-layer growth pattern. This can help to create SnSerelated heterojunctions with sharp interfaces. [23][24][25][26] Significantly, the absence of surface nonsaturated dangling bonds between adjacent two SnSe layers enables to reduce the spontaneous annihilation of photo excitons when used in heterojunction devices. This advantage offers a great opportunity for designing original optoelectronic devices with higher quantum efficiency as well.Note that the layered SnSe film as an absorber layer can achieve a higher optical absorption coefficient of ≈10 5 cm −1 , which is much larger than that of traditional Si or GaAs semiconductors by about two orders of magnitude. [5,[27][28][29][30] Furthermore, the specific band-gap of layered SnSe film was approximately 0.9 eV. This suggests that a thin layer of SnSe film could be sufficient to absorb a wide range of light, and generate a large amount of long-lived photoexcitons. Thus, owing to the excellent characteristics of light absorption and band-gap, the 2D layered SnSe crystalline film has become a suitable semiconductor for photodetection application. Compared to the exotic TCI phase SnSe crystal, the nondissipative surface electron transport with