Chu-Feng Chen

Experimental and Theoretical Demonstration on the Transport Properties of Fused Ring Host Materials for Organic Light-Emitting Diodes

The charge transport properties of three tertiary-butyl (t-Bu) substituted anthracene derivatives (ADN), critical blue host materials for organic light-emitting diodes (OLEDs), have been investigated experimentally and computationally. From time-of-flight (TOF) measurements, all ADN compounds exhibit ambipolar characters. The hole and electron mobilities are in the range (1–5)×10-7 cm2 V-1 s-1 under an external applied field of about 1 MV cm-1. Un-substituted ADN has the highest carrier mobilities while heavily t-Bu substituted ADN has the least. The electron and hole conducting properties of are consistent with ab initio calculation, which indicates that the frontier orbitals are localized mainly on the anthracene moiety. t-Bu substitutions in ADN increase the hopping path lengths among the molecules and hence reduce the electron and hole mobilities. The results demonstrate that t-Bu substitution is an effective means of engineering the conductivity of organic charge transporter for OLED applications.

Influence of Surface State on Biochemical Sensing Using SiGe Nanowire

Nanowires are extensively used to fabricate highly sensitive electrical sensors for detection of biological and chemical species. The hole mobility can be promoted by the increasing Ge fraction in SiGe, achieved by the oxidation-induced Ge condensation. However, oxidation increases the number of surface states, which brings the nonnegligible contribution in mobility degradation. In this work, 3-aminopropyltrimethoxysilane (APTMS) was used as a biochemical reagent to modify the surface of SiGe nanowires, then bonding to bio-linker, bis (3-sulfo-N-hydroxysuccinimide ester) sodium salt (BS3). Various methods have been proposed for increasing sensitivity of boron-doped SiGe nanowires, such as capping layer, surface treatment, and annealing temperature.

Sensitivity enhancement in SGOI nanowire biosensor fabricated by top surface passivation

Increasing the fraction of Ge in SiGe-on-Insulator (SGOI) using Ge condensation by oxidation significantly increases hole mobility. This effect can be exploited to improve the sensitivity of SGOI nanowire. However, our previous studies found that the sensitivity of an SGOI nanowire is degraded as the Ge fraction increases over 20%, because of the surface state of SiGe is unstable when the Ge fraction is high. In this work, a top surface passtivation SiO2 layer was deposited on an Si0.8Ge0.2 nanowire and successfully improve its sensitivity around 1.3 times that of the nanowire sample without top a passivation layer.

Effects of low-temperature Si buffer thickness and SiGe oxidation on sensitivity of Si1-xGex nanowire

Si1−xGex nanowire biosensors are attractive for their high sensitivity due to the large surface-to-volume ratio, high carrier mobility, and silicon compatibility. In this work, we study the effect of the thickness of the low-temperature Si (LT-Si) buffer layer on an insulator on the sensitivity of oxidized Si1−xGex nanowire samples with different Ge contents by increasing the Si buffer thickness from 20 to 60 nm. 3-Aminopropyltrimethoxysilane (APTMS) was used as a biochemical reagent. It was demonstrated that, with the proper Ge content and LT-Si buffer thickness, the sensitivity of the Si1−xGex nanowire is high and it can be further improved by Si1−xGex oxidation. This can be attributed to the reduction of the diameter to the nanometer order, which gives rise to an increased surface-to-volume ratio and further enhances the sensitivity of the biosensor.

Self-Passivation by Fluorine Plasma Treatment and Low-Temperature Annealing in SiGe Nanowires for Biochemical Sensors

Nanowires are widely used as highly sensitive sensors for electrical detection of biological and chemical species. Modifying the band structure of strained-Si metal-oxide-semiconductor field-effect transistors by applying the in-plane tensile strain reportedly improves electron and hole mobility. The oxidation-induced Ge condensation increases the Ge fraction in a SiGe-on-insulator (SGOI) and substantially increases hole mobility. However, oxidation increases the number of surface states, resulting in hole mobility degradation. In this work, 3-aminopropyltrimethoxysilane (APTMS) was used as a biochemical reagent. The hydroxyl molecule on the oxide surface was replaced by the methoxy groups of the APTMS molecule. We proposed a surface plasma treatment to improve the electrical properties of SiGe nanowires. Fluorine plasma treatment can result in enhanced rates of thermal oxidation and speed up the formation of a self-passivation oxide layer. Like a capping oxide layer, the self-passivation oxide layer reduces the rate of follow-up oxidation. Preoxidation treatment also improved the sensitivity of SiGe nanowires because the Si-F binding was held at a more stable interface state compared to bare nanowire on the SiGe surface. Additionally, the sensitivity can be further improved by either the N2 plasma posttreatment or the low-temperature postannealing due to the suppression of outdiffusion of Ge and F atoms from the SiGe nanowire surface.

Effects of sensitivity enhancement by oxide passivation layer on SGOI nanowire fabrication

Increasing the fraction of Ge in SiGe-on-Insulator (SGOI) using Ge condensation by oxidation significantly increases hole mobility. This effect can be exploited to improve the sensitivity of SGOI nanowire. However, our previous studies found that the sensitivity of an SGOI nanowire is degraded as the Ge fraction increases over 20%, because of the surface state of SiGe is unstable when the Ge fraction is high. In this work, a top surface passtivation SiO2 layer was deposited on an Si0.8Ge0.2 nanowire and successfully improve its sensitivity around 2.5 times that of the nanowire sample without top a passivation layer.

Oxidation and structure scheme studies for sensitivity improvement of Si 1−x Ge x nanowire biosensor

Because of the large surface-to-volume ratio of nano-structure, the silicon nanowires (SiNWs) provide a high sensitivity for highly sensitive detection of biological and chemical species. Moreover, the SiGe-on-Insulator (SGOI) by Ge-condensation process can enhance the mobility of hole carrier and then improve the nanowiress conductance. In this study, we discuss SiGe nanowire structural effect by changing Si/SiGe stacked ratio and oxidation effect in different annealing ambient. The optimized Si/SiGe stacked structure with suitable oxidation process has more twice enhancement of sensitivity compared to conventional SiNWs biosensor.