Broadband SnS/Te photodetector to long-wavelength infrared: breaking the spectrum limit through alloy engineering.

Materials based on group IV chalcogenides, are considered to be one of the most promising materials for high-performance, broadband photodetectors due to their wide bandgap coverage, intriguing chemical bonding and excellent physical properties. However, the reported photodetectors based on SnS are still worked at relatively narrow near-infrared band (as far as 1550 nm) hampered by the nonnegligible bandgap of 1.1-1.5 eV. Here, a novel photodetector based on Te alloyed SnS thin film was demonstrated with an ultra-broadband response up to 10.6 µm. By controlling the Te alloyed concentration in SnS increasing to 37.64%, the bandgap narrows to 0.23 eV, exhibiting a photoresponse potential at long-wavelength infrared excitation. Our results show Te-alloying can remarkably enhance the detection properties of SnS/Te photodetectors. The photoresponsivity and detectivity of 1.59 mA/W and 2.3 × 108 Jones were realized at 10.6 µm at room temperature. Moreover, the nonzero photogain was observed generated by nonlinearly increased photocurrent density, resulting in a superlinear dependency between photoresponsivity and light intensity. Our studies successfully broaden photoresponse spectrum of SnS toward the mid-infrared range for the first time. It also suggests that alloying is an effective technique for tuning the band edges of group IV chalcogenides, contributing deep implications for developing future optoelectronic applications.

Strong, anisotropic, layer-independent second harmonic generation in multilayer SnS film.

Materials based on group IV chalcogenides exhibit extensive technologically important properties. Its unusual chemical bonding and off-centering of in-layer sublattices could cause chemical polarity and weakly broken symmetry, making optical field controlling feasible. Here, we fabricated large-area SnS multilayer films and observed unexpected strong SHG response at 1030 nm. The appreciable SHG intensities were obtained with an independence on layer, which is opposite to the generation principle of overall nonzero dipole moment only in odd-layer material. Taking GaAs for reference, the second-order susceptibility was estimated to be 7.25 pm/V enhanced by mixed-chemical bonding polarity. Further polarization-dependent SHG intensity confirmed the crystalline orientation of SnS films. The results imply surface inversion symmetry broken and nonzero polarization field modified by metavalent bonding should be the origin of SHG responses. Our observations establish multilayer SnS as a promising nonlinear material, and will guide in design of IV chalcogenides with improved optics and photonics properties for the potential applications.