We investigated the impact of the passivation layer on the stability of indium-gallium-zinc oxide (IGZO) thin film transistors. While the device without any passivation layer showed a huge threshold voltage (Vth) shift under positive gate voltage stress, the suitably passivated device did not exhibit any Vth shift. The charge trapping model, which has been believed to be a plausible mechanism, cannot by itself explain this behavior. Instead, the Vth instability was attributed to the interaction between the exposed IGZO backsurface and oxygen and/or water in the ambient atmosphere during the gate voltage stress.

The authors report the fabrication of high performance thin film transistors (TFTs) with an amorphous indium gallium zinc oxide (a-IGZO) channel, which was deposited by cosputtering using a dual IGZO and indium zinc oxide (IZO) target. The effect of the indium content on the device performance of the a-IGZO TFTs was investigated. At a relatively low IZO power of 400W, the field-effect mobility (μFE) and subthreshold gate swing (S) of the a-IGZO TFTs were dramatically improved to 19.3cm2∕Vs and 0.35V/decade, respectively, compared to those (11.2cm2∕Vs and 1.11V/decade) for the TFTs with the a-IGZO channel (reference sample) prepared using only the IGZO target. The enhancement in the subthreshold IDS-VGS characteristics at an IZO power of 400W compared to those of the reference sample was attributed to the reduction of the interface trap density rather than the reduction of the bulk defects of the a-IGZO channel.

The effect of the channel deposition pressure on the device performance of amorphous indium-gallium-zinc oxide ͑a-IGZO͒ transistors was investigated in detail. The performance of the fabricated transistors improved monotonously with decreasing chamber pressure: at a pressure of 1 mTorr, the field-effect mobility ͑ FE ͒ and subthreshold gate swing ͑S͒ of the a-IGZO thin-film transistors were dramatically improved to 21.8 cm 2 /Vs and 0.17 V/decade, respectively, compared to those ͑11.4 cm 2 /Vs and 0.87 V/decade͒ of the reference transistors prepared at 5 mTorr. This enhancement in the subthreshold characteristics was attributed to the reduction of the bulk defects of the a-IGZO channel, which might result from the greater densification of the a-IGZO films at the lower deposition pressure.In recent years, amorphous indium gallium zinc oxide ͑a-IGZO͒ has gained much attention as an attractive channel material for transparent thin-film transistors ͑TFTs͒, because it provides high mobility and good transparency, as well as a low-temperature process that allows the fabrication of TFTs and circuits on flexible substrates such as plastic. 1-4 For the mobile application of flexible displays, low power consumption is one of the key issues, 5 owing to the weight and size of the rechargeable lithium-ion battery used as a power source. An effective method of reducing the power consumption is to improve the characteristics of subthreshold gate swing ͑S͒ and, thus, to diminish the driving voltage range. Because the value of S is largely determined by the total trap density of the field-effect transistor with a metal-insulator-semiconductor structure, 6 it is important to understand the relation between the oxide channel deposition and the bulk trap density of the oxide semiconductor. Although the effect of oxygen pressure and radio-frequency ͑rf͒ power on the conductivity of oxide thin films such as ZnO, IZO, and a-IGZO has been investigated in detail, 2,7-9 very little is known about the fundamental relation between their material properties ͑e.g., composition and density͒ and their trap density and/or the subthreshold gate swing of transistors. In our previous article, it was shown that the transport properties such as field-effect mobility can be improved by optimizing the cation composition of the channel layer. 10 Moreover, the value of S was enhanced to 0.36 V/decade by choosing the proper In/Ga ratio, which was attributed to the reduction of the interfacial trap density rather than the bulk trap density. However, it is still not clear how the structural properties such as the surface roughness and the density of the a-IGZO thin film are influenced by the deposition condition and their effect on the electrical properties such as field-effect mobility and gate swing of the transistors.In this article, we report the fabrication of a-IGZO TFTs with an excellent gate swing of 0.17 V/decade, which was achieved by simply reducing the chamber pressure. It was shown that the densification of the a-IGZO semiconductor resulted in ...

The full color 12.1‐inch WXGA active‐matrix organic light emitting diode (AMOLED) display was, for the first time, demonstrated using indium‐gallium‐zinc oxide (IGZO) thin‐film transistors (TFTs) as an active‐matrix back plane. It was found that the fabricated AMOLED display did not suffer from the well‐known pixel non‐uniformity of luminance, even though the simple structure consisting of 2 transistors and 1 capacitor was adopted as a unit pixel circuit, which was attributed to the amorphous nature of IGZO semiconductor. The n‐channel a‐IGZO TFTs exhibited the field‐effect mobility of 8.2 cm2/Vs, threshold voltage of 1.1 V, on/off ratio of > 108, and subthreshold gate swing of 0.58 V/decade. The AMOLED display with a‐IGZO TFT array would be promising for large size applications such as note PC and HDTV because a‐IGZO semiconductor can be deposited on large glass substrate (> Gen. 7) using conventional sputtering system.

Electronic excitations in nominally undoped GaN have been investigated by Raman scattering. Peaks in the range between 18.5 and 30 meV have been assigned to internal shallow donor transitions in cubic and hexagonal GaN, respectively. The photon energy dependence of the scattering efficiencies in the cubic phase is explained by Raman scattering in resonance with the so-called ‘‘yellow’’ luminescence transitions. This interpretation supports models for the notorious yellow luminescence in which shallow donors are involved. These shallow donors most likely do not originate from native point defects.