We reported the analysis and modeling of some conduction mechanisms in ultrathin aluminum oxide (Al2O3) films of 6 nm thickness, which are deposited by atomic layer deposition (ALD). This modeling included current-voltage measurements to metal-insulator-semiconductor (MIS) capacitors with gate electrode areas of 3.6 × 10−5 cm2 and 6.4 × 10−5 cm2 at room temperature. The modeling results showed the presence of ohmic conduction, Poole Frenkel emission, Schottky emission, and trap-assisted tunneling mechanisms through the Al2O3 layer. Based on extracted results, we measured a dielectric conductivity of 5 × 10−15 S/cm at low electric fields, a barrier height at oxide/semiconductor interface of 2 eV, and an energy trap level into bandgap with respect to the conduction band of 3.11 eV. These results could be affected by defect density related to oxygen vacancies, dangling bonds, fixed charges, or interface traps, which generate conduction mechanisms through and over the dielectric energy barrier. In addition, a current density model is developed by considering the sum of dominant conduction mechanisms and results based on the finite element method for electronic devices, achieving a good match with experimental data.
Thin film transistors (TFTs) fabricated on flexible and large area substrates have been studied with great interest due to their future applications. Recent studies have developed new semiconductors such as a-SiGe:H for fabrication of high performance TFTs. These films have important advantages, including deposition at low temperatures and low pressures, and higher carrier mobilities. Due to these advantages, the a-SiGe:H films can be used in the fabrication of TFTs. In this work, we present an analytical drain current model for a-SiGe:H TFTs considering density of states and free charges, which describes the current behavior at sub-and above- threshold region. In addition, 2D numerical simulations of a-SiGe:H TFTs are developed. The results of the analytical drain current model agree well with those of the 2D numerical simulations. For all characteristics of the drain current curves, the average absolute error of the analytical model is close to 5.3%. This analytical drain current model can be useful to estimate the performance of a-SiGe:H TFTs for applications in large area electronics.
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