Dei Wei Chou

Pentacene-Based Thin-Film Transistors With a Solution-Process Hafnium Oxide Insulator

Pentacene-based organic thin-film transistors with solution-process hafnium oxide (HfOx) as gate insulating layer have been demonstrated. The solution-process HfOx could not only exhibit a high-permittivity (kappa = 11) dielectric constant but also has good dielectric strength. Moreover, the root-mean-square surface roughness and surface energy (gammas) on the surface of the HfOx layer were 1.304 nm and 34.24 mJ/cm2, respectively. The smooth, as well as hydrophobic, surface of HfOx could facilitate the direct deposition of the pentacene film without an additional polymer treatment layer, leading to a high field-effect mobility of 3.8 cm2/(V middots) .

AlGaN/GaN Metal Oxide Semiconductor Heterostructure Field-Effect Transistor Based on a Liquid Phase Deposited Oxide

AlGaN/GaN metal oxide semiconductor heterostructure field-effect transistors (MOSHFETs) with liquid phase deposited SiO2 as the insulating gate are demonstrated. A very large gate swing voltage is applied. An AlGaN/GaN MOS heterostructure FET with saturation characteristics is observed. For a gate length of 2 µm in a 5 µm channel opening with a gate width of 100 µm, MOSHFET with transconductance and maximum drain current of 78 mS/mm and 720 mA/mm, respectively, is achieved.

Liquid phase deposited SiO2 on GaN

Abstract An efficient and low cost approach to deposit uniform silicon dioxide layers on GaN by liquid phase deposition (LPD) near room temperature are described and discussed. The process is simple. GaN wafers are immersed into a H2SiF6 and H3BO3 solution to form the silicon dioxide layers. The deposition conditions and the properties of the SiO2 films will be characterized.

Effect of crystal orientation and doping on the activation energy for GaAs oxide growth by liquid phase method

We have investigated the oxide growth kinetics of near-room-temperature liquid phase chemical enhanced oxidation on differently oriented and doped GaAs substrates. Oxidation reactions have been studied by analyzing their activation energies and have been found to depend on the bond configuration of crystal planes. Experimental results indicate that the activation energies are independent of the doping of GaAs. The oxidation rates are dopant selective (n−:p+-GaAs∼4:1 at 30u200a°C under illumination) and sensitive to illumination (without:with illumination∼1:25 at 30u200a°C for a n+-doped GaAs). In the oxidation reactions, photogenerated holes are found to play an important role. Finally, we have proposed a mechanism based on the band bending and the carrier transport near the oxide-GaAs interface to interpret the experimental observations.

Surface Oxidation Kinetics of GaAs Oxide Growth by Liquid Phase Chemical-Enhanced Technique

The initial stage of GaAs oxidation by a near-room-temperature liquid phase chemical-enhanced technique has been studied. Based on the experimental results of X-ray photoelectron spectroscopy, a complete model illustrating the chemical composition of the grown oxide film has been established. To clarify the kinetics of oxide growth in a liquid solution in more detail, we have also performed selective oxidation and surface profile measurements. Unusual features of the oxide growth kinetics have been observed by investigating the physical structure of oxide at the edge of mask in the selective oxidation.

Electrical properties of GaAs metal-oxide-semiconductor structures with the oxide layer grown by liquid phase chemical-enhanced method

Abstract The oxide films prepared by liquid phase chemical-enhanced technique were electrically characterized using current–voltage and capacitance–voltage measurements on metal-oxide-semiconductor (MOS) structure. It was found that the leakage current density is roughly (1–2)×10 −6 xa0Axa0cm −2 at the electric filed of 1xa0MVxa0cm −1 . The oxides with denser structures exhibit higher refractive indices, higher reliability and also higher breakdown voltages. The breakdown fields of ∼7xa0MVxa0cm −1 were obtained as refractive index is ∼2.12. In addition, dielectric constant of oxide films is found to increase with increasing thickness and varies within a wide range from 3.2 to 11 under accumulation region. Furthermore, short time ramp-voltage, constant-voltage and constant-current stress are employed to reliability study.

Influence of inserting a thin fullerene layer on pentacene organic thin-film transistor

The performance of organic thin-film transistors (TFTs) with a pentacene/fullerene(C60)/pentacene (PCP) sandwich structure is presented. Using a 3.5u2009nm-thick C60 layer inserted between the pentacene films, the obtained hole mobility is improved by more than six times. By applying atomic force microscopy, x-ray diffraction, Raman spectrum, and transmission line method analysis, one can reasonably infer that the smoother surface of the pentacene film covered with thin C60 layer delays the phase transformation of the upper pentacene film, resulting in stronger intermolecular coupling and the reduction of channel resistance of the PCP TFTs from 3.03 to 1.72 MΩ, and, therefore, improving the device performance.

Study of diffusion barriers for Au metal on liquid phase oxidized GaAs

TiW, TiN, Pd, and Mo as the diffusion barriers (DBs) in Au/DB/GaAs native oxide multilayer structures are investigated. The GaAs native oxides are prepared by liquid phase oxidation, and the results indicate that TiW and Mo films can effectively block Au diffusion at temperatures of up to 550°C for 30min. However, TiN and Pd films can effectively block Au diffusion only at 450°C for 30min. The failure of TiN and Pd appears related to the embedded oxygen in the barrier layers which cause the interdiffusion between Au and the barrier films. In comparison, TiW and Mo show better blocking properties that prevent Au from diffusing into oxide films. They also act as a diffusion barrier even at temperatures above 550°C.