High-performance UV-B detectors based on Mn_xZn_1-xS thin films modified by bandgap engineering

The high-speed performance ultraviolet (UV) detectors were successfully fabricated based on the ternary Mn_xZn_1-xS (0.2 ≤ x ≤ 0.4) thin films deposited by a simple spray pyrolysis method. The optoelectrical properties of the samples were modified by introducing the Mn impurities at high content to enhance the performance of UV detectors. Microstructural characteristics confirmed the well-incorporation of Mn²⁺ ions into the ZnS lattice having nanocrystalline nature with homogeneous surface and strong adherence to the substrates. The optical measurements revealed that at the higher Mn²⁺ concentration, the optical transmittance increased over 95 % in the visible to near-infrared regions. Compared to the pure ZnS, the values of bandgap energy were found to blue-shift about 0.14 eV due to both quantum confinement and Burstein-Moss theories. Meanwhile, the Urbach energy decreased dramatically, leading to a considerable reduction of the electron-phonon interaction. The photoluminescence (PL) spectra revealed that the PL emission intensity was enhanced by introducing excess charge carriers through increasing the Mn²⁺ concentration, which can improve the generation of electron-hole pairs in the alloys. The photoresponse characterization featured a tremendous photosensing and photoswitching for the fabricated UV detectors, in which an excellent UV-B responsivity and high visible rejection were observed for the devices. For the UV detector based on the Mn_0.4Zn_0.6S thin film, the current gain greatly improved over 4.5 times compared to the pure ZnS one. Likewise, the photoresponse speed of the samples was found to enhance over 5 times, considerably.