Design and characterization of Ge/SeO2 heterojunctions as tunneling thin film transistors

Herein stacked layers of germanium and selenium oxide are employed to fabricate heterojunction devices that can perform as a multifunctional thin film transistors (TFT). The stacked layers of Ge and SeO2 are coated onto ultrasonically cleaned glass and Ag thin film substrates using thermal deposition technique under a vacuum pressure of 1.5 mbar. The stacked layers are structurally, morphologically, optically and electrically characterized. It is observed that while amorphous germanium films exhibit two energy band gaps of values of 3.56 and 0.78 eV, amorphous SeO2 show one band gap of 3.70 eV. The conduction and valence band offsets at the Ge/SeO2 interfaces are 2.24 eV and 0.68 eV, respectively. Optically, the coating of SeO2 onto Ge films enhanced the light absorbability of SeO2 by ~ 50 times (at 2.38 eV) and ~17 times (at 1.71 eV) in the visible and infrared ranges of light, respectively. Formation of Ge/SeO2 is associated with a redshift and blue shift in the values of the energy band gaps of SeO2 and Ge, respectively. In addition, the current-voltage characteristic curve analyses have shown that Ag/Ge/SeO2/Ag TFTs is of tunneling type showing an estimated peak to valley current ratios of 2.0. The TFT displayed additional functionalities presented by PMOS characteristics, microwave resonators, negative capacitance sources and multiband band stop filters. The features of the devices nominate them for use in microwave technology as band stop filters of notch frequencies of 1.10 and 1.53 GHz.