Many challenges exist in understanding transport properties in metal-oxide thin film transistors (MO-TFTs). Microstructural disorder, dielectric/active layer interface trap states, and grain boundaries contribute to reductions in device properties such as transistor output current, mobility, and sheet carrier concentration. In this work, we use scheduled interruptions during atomic layer deposition combined with a series of thermal anneals to control properties of ZnO/ A l 2 O 3 TFTs, and to experimentally decouple physical effects within the TFT affecting device performance. Using concurrent current–voltage and gated Hall effect measurements, we observe two sets of trends for these devices. In the first, increasing post-temperature anneal is shown to improve the device characteristics by reducing grain boundary effects. In the second, exposure to ambient conditions is shown to increase the number of interface trap states. Comparisons of measured values show that these trap states enhance some properties of the lower temperature annealed series, while degrading these values in the higher temperature annealed series. We show that this is due to devices acting in two separate transport regimes: localized, and non-localized. We investigate the position of the Fermi level, adjusted by gate bias, to these two regimes under each test condition, and suggest a simple model to describe the results.

InGaZnO (IGZO) is an excellent semiconductor material for thin-film transistors (TFTs) used in direct-current and radio-frequency (RF) switching applications, especially since it can be grown at low temperatures on a wide variety of substrates. IGZO thin films with a composition of InGaZnO4 have been deposited and used as channel layers in TFTs for many applications to date; however, IGZO compositions can also be easily changed to vary their properties. These different compositions of IGZO may have different defect properties. In this study, we report the growth of IGZO with composition of In2O3:Ga2O3:5ZnO (In2Ga2Zn5O11) by pulsed laser deposition (PLD) and its electronic defects studied by thermally stimulated current (TSC) spectroscopy. It was found that the as-grown sample has a DC activation energy of 0.62 eV, and four major traps with activation energies between similar to 0.16-0.50 eV and one at similar to 0.90 eV. Electrical properties and the deep traps of PLD-grown IGZO thin film were found to be varied by post-processing conditions such as thermal history and measurement conditions such as the bias and light exposure applied to the samples. The instabilities induced by these conditions can be explained by structural and stoichiometric features-the ZnO4 tetrahedra and GaO6 octahedra in the structure may become distorted, caused by oxidation or reduction, so that the different defect states could be changed and/or lattice energy variations from the distortion can be observed. This work demonstrates that current-based trap emission, such as that associated with TSC, can effectively reveal electronic defects in highly-resistive semiconductor materials, especially those that are not amenable to capacitance-based techniques, such as deep-level transient spectroscopy, and provide an effective manner to study the trap instabilities in IGZO.

Two methods of measuring the electronic transport properties of a material are transistor DC-voltage and the Hall effect. Hall mobility measurements of normally off semiconductors can be done by electrostatic doping to lower resistance in the channel. We show that by measuring both, we can compare any value (raw measured as well as calculated data) directly to any other value along an index of FET gate and drain voltage across the entire safe operating area of the device. Our gated Hall technique intrinsic calculations of Hall mobility, typically possible only for bulk or doped materials, for thin-film transistor materials stack up with thickness scaled to practical values.

InGaZnO (IGZO) is a promising semiconductor material for thin-film transistors (TFTs) used in DC and RF switching applications, especially since it can be grown at low temperatures on a wide variety of substrates. Enhancement-mode TFTs based on IGZO thin films grown by pulsed laser deposition (PLD) have been recently fabricated and these transistors show excellent performance; however, compositional variations and defects can adversely affect film quality, especially in regard to electrical properties. In this study, we use thermally stimulated current (TSC) spectroscopy to characterize the electrical properties and the deep traps in PLD-grown IGZO thin films. It was found that the as-grown sample has a DC activation energy of 0.62 eV, and two major traps with activation energies at similar to 0.16-0.26 eV and at similar to 0.90 eV. However, a strong persistent photocurrent (PPC) sometimes exists in the as-grown sample, so we carry out post-growth annealing in an attempt to mitigate the effect. It was found that annealing in argon increases the conduction, produces more PPC and also makes more traps observable. Annealing in air makes the film more resistive, and removes PPC and all traps but one. This work demonstrates that current-based trap emission, such as that associated with the TSC, can effectively reveal electronic defects in highly-resistive semiconductor materials, especially those are not amenable to capacitance-based techniques, such as deeplevel transient spectroscopy (DLTS).