States In Energy Band Gap Research Articles

Effect of Silicon Doping on the Electrical Performance of Amorphous SiInZnO Thin-film Transistors

The change of the electrical properties of amorphous SiInZnO thin-film transistors (SIZO TFTs) depending on Si concentration have been investigated. As the Si content increased from 1 to 3 wt%, the electrical properties are systematically degraded, such as field-effect mobility from 19.86 to 11.16 cm2 V−1 s−1. This change in properties has been found to deteriorate the SIZO network when Si content is highly added. In order to analyze the change of the electrical properties of SIZO depending on Si concentration, low frequency noise method and X-ray photoelectron spectroscopy analysis are adopted to investigate trap states in energy bandgap and oxygen vacancies of SIZO system. As a result, it was found that doping with a large amount of Si destabilizes the SIZO network, resulting in degrading electrical properties.

Ultrasensitive yttrium modified tin oxide thin film based sub-ppb level NO2 detector

Considering the adverse effect of rising air pollution on environment and human health, highly selective and trace level sensors are needed. Herein, yttrium (Y) incorporated tin oxide (SnO2) thin film gas sensors have been developed for sub-ppb level detection of NO2 at room-temperature. The undoped and Y-doped (1, 3 and 5 wt%) thin films have been prepared via electron beam deposition technique. The XPS studies confirmed the substitution of Sn with Y in SnO2 lattice. The morphological and structural characterizations reveal smooth and crystalline thin films, while Raman and PL spectroscopic studies confirm the presence and growth of oxygen vacancies (OVs), specifically in-plane OVs, in doped samples. Moreover, narrowing of electron absorption spectra in doped samples implied the formation of mid-gap states in energy bandgap of SnO2 leading to enhanced electron transfer. The 3 wt% Y-doped SnO2 sensor exhibited excellent sensing response with high selectivity towards NO2 in 15–240 ppb range. The sensors also showed high stability and repeatability along with humidity insensitivity. Notably, the sensor was observed to be highly sensitive to 0.6 ppb NO2 exhibiting a 26 % response along with response/recovery time of 4/2 min. The improved sensing characteristics have been ascribed to reduced crystallite size, elevated in-plane OVs, enhanced charge transfer and increased specific surface area due to Y integration.

Investigation on energy bandgap states of amorphous SiZnSnO thin films

The variation in energy bandgaps of amorphous oxide semiconducting SiZnSnO (a-SZTO) has been investigated by controlling the oxygen partial pressure (Op). The systematic change in Op during deposition has been used to control the electrical characteristics and energy bandgap of a-SZTO. As Op increased, the electrical properties degraded, while the energy bandgap increased systematically. This is mainly due to the change in the oxygen vacancy inside the a-SZTO thin film by controlling Op. Changes in oxygen vacancies have been observed by using X-ray photoelectron spectroscopy (XPS) and investigated by analyzing the variation in density of states (DOS) inside the energy bandgaps. In addition, energy bandgap parameters, such as valence band level, Fermi level, and energy bandgap, were extracted by using ultraviolet photoelectron spectroscopy, Kelvin probe force microscopy, and high-resolution electron energy loss spectroscopy. As a result, it was confirmed that the difference between the conduction band minimum and the Fermi level in the energy bandgap increased systematically as Op increases. This shows good agreement with the measured results of XPS and DOS analyses.