Effects of ZnPc substrates on the electro‑optical properties of MgSe thin films and the applications of Al/ZnPc/MgSe/ (Ag, C, Au) hybrid devices as resonant negative capacitance sources

Abstract

Herein, polycrystalline magnesium selenide (MgSe) thin films are deposited onto glass and monoclinic-structured zinc phthalocyanine (ZnPc) thin film substrates under high vacuum pressure using the thermal evaporation technique. ZnPc substrates improved the crystallinity of the MgSe films and decreased the stacking faults percentages and defect concentration by 31.57 and 52.49%, respectively. MgSe films deposited onto ZnPc substrates exhibited a notable increase of up to 32% in light absorption within the visible spectrum, while maintaining the energy band gap value of MgSe without significant alteration. In addition, as both the substrate and the epilayer exhibited p-type conductivity, an isotype heterojunction device structure is formed at the ZnPc/MgSe interfaces. The valence and conduction band offsets for this interface are 0.81 and 1.16 eV, respectively. On the other hand, re-fabrication of the ZnPc/MgSe heterojunctions onto Al thin film substrates and forming three Ag/MgSe, C/MgSe, and Au/MgSe Schottky channels on the epilayer surface allowed wide control of the negative capacitance effect and the resonance-antiresonance (RA) peaks in the capacitance spectra of the Al/ZnPc/MgSe/(Ag, C, Au) hybrid devices. These two important RA and NC features of the device can also be engineered by altering the DC biasing of the device. Moreover, Lorentz model analyses on the capacitance spectra showed an increased density of oscillators and increased scattering time constant with decreasing built-in potential at the metal/MgSe interfaces. The features of the hybrid devices presented make the device promising for microwave and electro-optical applications.