Nanometer-Thick Metastable Zinc Blende γ-MnTe Single-Crystalline Films for High-Performance Ultraviolet and Broadband Photodetectors

Van der Waals heteroepitaxial (vdWE) has been intensely developed and considered as the most promising heteroepitaxial technique for growth of high-quality nanoscale films, covalent-bonded semiconductor films, and heterostructures to create the next-generation flexible electronic/optoelectronic devices because of its nature of relief of the strict requirement of lattice matching and its elegant exfoliation and transfer to any substrates of interest. However, application of the vdWE route in growing metastable and artificial materials and structures is still absent. In this work, by using the molecular beam epitaxy (MBE), epitaxy of metastable γ-phase nanometer-thick MnTe thin films is achieved on two-dimensional mica substrates through attentive control of its growth kinetics. The good crystallinity of vdWE γ-MnTe thin films is shown by a low half peak width value of about 0.19° for 50 nm-thick epitaxial films. Moreover, a structure with perfect lattice, a wide Egopt of μ3.26 eV with the direct electron transition structure, a broad absorption region from ultraviolet (UV) to near-infrared (NIR), and an ultrahigh absorption coefficient beyond 106 cm-1 in the UV region are found in vdWE nanometer-thick γ-MnTe thin films. The photodetectors with vdWE γ-MnTe/mica systems exhibit a highly sensitive broadband detecting from the UV to the NIR region. The detectors show an outstanding UV response with a high responsivity of 526 A W-1 and specific detectivity of 2.46 × 1012 Jones and show fast photoresponse speeds (τrising = 1.9 ms and τdecay = 1.7 ms) under a 375 nm laser illumination that indicate a great potential in flexible UV and broad spectrum detection of the photodetectors with vdWE nanometer-thick γ-MnTe/mica.