Monthly Archives: December 2014

Solution Processed F Doped ZnO (ZnO:F) for Thin Film Transistors and Improved Stability Through Co-Doping with Alkali Metals

J. Mater. Chem. C, 2014, Accepted ManuscriptDOI: 10.1039/C4TC02257B, PaperJing-Jing Chang, Zhen-Hua Lin, Ming Lin, Chun-Xiang Zhu, Jie Zhang, Jishan WuThis paper reported solution-processed metal oxide semiconductor thin film transistors (TFTs) which were produced using fluorine (F) doped ZnO-based aqueous solution. It was found that doping F in ZnO film...The content of this RSS Feed (c) The Royal Society of Chemistry

Electronic and optical device applications of hollow cathode plasma assisted atomic layer deposition based GaN thin films

Electronic and optoelectronic devices, namely, thin film transistors (TFTs) and metal–semiconductor–metal (MSM) photodetectors, based on GaN films grown by hollow cathode plasma-assisted atomic layer deposition (PA-ALD) are demonstrated. Resistivity of GaN thin films and metal-GaN contact resistance are investigated as a function of annealing temperature. Effect of the plasma gas and postmetallization annealing on the performances of the TFTs as well as the effect of the annealing on the performance of MSM photodetectors are studied. Dark current to voltage and responsivity behavior of MSM devices are investigated as well. TFTs with the N2/H2 PA-ALD based GaN channels are observed to have improved stability and transfer characteristics with respect to NH3 PA-ALD based transistors. Dark current of the MSM photodetectors is suppressed strongly after high-temperature annealing in N2:H2 ambient.

Remarkable changes in interface O vacancy and metal-oxide bonds in amorphous indium-gallium-zinc-oxide thin-film transistors by long time annealing at 250 °C

We have studied the effect of long time post-fabrication annealing on negative bias illumination stress (NBIS) of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film-transistors. Annealing for 100 h at 250 °C increased the field effect mobility from 14.7 cm2/V s to 17.9 cm2/V s and reduced the NBIS instability remarkably. Using X-ray photoelectron spectroscopy, the oxygen vacancy and OH were found to exist at the interfaces of a-IGZO with top and bottom SiO2. Long time annealing helps to decrease the vacancy concentration and increase the metal-oxygen bonds at the interfaces; this leads to increase in the free carrier concentrations in a-IGZO and field-effect mobility. X-ray reflectivity measurement indicated the increment of a-IGZO film density of 5.63 g cm−3 to 5.83 g cm−3 (3.4% increase) by 100 h annealing at 250 °C. The increase in film density reveals the decrease of O vacancy concentration and reduction of weak metal-oxygen bonds in a-IGZO, which substantially helps to improve the NBIS stability.

Exploring SiSn as a performance enhancing semiconductor: A theoretical and experimental approach

We present a novel semiconducting alloy, silicon-tin (SiSn), as channel material for complementary metal oxide semiconductor (CMOS) circuit applications. The material has been studied theoretically using first principles analysis as well as experimentally by fabricating MOSFETs. Our study suggests that the alloy offers interesting possibilities in the realm of silicon band gap tuning. We have explored diffusion of tin (Sn) into the industry's most widely used substrate, silicon (100), as it is the most cost effective, scalable and CMOS compatible way of obtaining SiSn. Our theoretical model predicts a higher mobility for p-channel SiSn MOSFETs, due to a lower effective mass of the holes, which has been experimentally validated using the fabricated MOSFETs. We report an increase of 13.6% in the average field effect hole mobility for SiSn devices compared to silicon control devices.

Assessing the width of Gaussian density of states in organic semiconductors

Publication date: February 2015 Source:Organic Electronics, Volume 17 Author(s): Francesco Maddalena , Carlo de Falco , Mario Caironi , Dario Natali The Density of States (DOS) is an ingredient of critical importance for the accurate physical understanding of the optoelectronic properties of organic semiconductors. The disordered nature of this class of materials, though, renders the task of determining the DOS far from trivial. Its extraction from experimental measurements is often performed by driving the semiconductor out of thermal equilibrium and therefore requires making assumptions on the charge transport properties of the material under examination. This entanglement of DOS and charge transport models is unfavorable since transport mechanisms in organic semiconductors are themselves still subject of debate. To avoid this, we propose an alternative approach which is based on populating and probing the DOS by means of capacitive coupling in Metal Insulator Semiconductors (MIS) structures while keeping the semiconductor in thermal equilibrium. Assuming a Gaussian shape, we extract the DOS width by numerical fitting of experimental Capacitance–Voltage curves, exploiting the fact that the DOS width affects the spatial distribution of accumulated charge carriers which in turn concurs to define the MIS capacitance. The proposed approach is successfully tested on two benchmark semiconducting polymers, one of n-type and one of p-type and it is validated by verifying the robustness of the extraction procedure with respect to varying the insulator electrical permittivity. Finally, as an example of the usefulness and effectiveness of our approach, we study the static characteristics of thin film transistors based on the aforementioned polymers in the framework of the Extended Gaussian Disorder transport model. Thanks to the extracted DOS widths, the functional dependence of current on the gate voltage is nicely predicted and physical insight on transistor operation is achieved. Graphical abstract

Exploring SiSn as a performance enhancing semiconductor: A theoretical and experimental approach

We present a novel semiconducting alloy, silicon-tin (SiSn), as channel material for complementary metal oxide semiconductor (CMOS) circuit applications. The material has been studied theoretically using first principles analysis as well as experimentally by fabricating MOSFETs. Our study suggests that the alloy offers interesting possibilities in the realm of silicon band gap tuning. We have explored diffusion of tin (Sn) into the industry's most widely used substrate, silicon (100), as it is the most cost effective, scalable and CMOS compatible way of obtaining SiSn. Our theoretical model predicts a higher mobility for p-channel SiSn MOSFETs, due to a lower effective mass of the holes, which has been experimentally validated using the fabricated MOSFETs. We report an increase of 13.6% in the average field effect hole mobility for SiSn devices compared to silicon control devices.

Lowering Contact Resistance by SWCNT-Al Bilayer Electrodes in Solution Processable Metal-Oxide Thin Film Transistor

J. Mater. Chem. C, 2014, Accepted ManuscriptDOI: 10.1039/C4TC02431A, PaperSu Jeong Lee, Tae Il Lee, Jee-Ho Park, Il-Kwon Oh, Hyungjun Kim, Jung Han Kim, Chul-Hong Kim, GeeSung Chae, Hong Koo Baik, Jae-Min MyoungWe introduced a single-wall carbon nanotube (SWCNT)-Al bilayer as electrodes for the high-performance solution processable thin film transistor (TFT). The contact resistance was systematically lowered by inserting an Al layer...The content of this RSS Feed (c) The Royal Society of Chemistry

Optimization of nanocomposite gate insulators for organic thin film transistors

Publication date: February 2015 Source:Organic Electronics, Volume 17 Author(s): Sooman Lim , Keun Hyung Lee , Hyekyoung Kim , Se Hyun Kim Nanocomposite gate insulators consisting of (Ba, Sr)TiO3 (barium strontium titanate; BST) nanoparticles and crosslinked poly(4-vinyl phenol) (PVP) polymers were fabricated. Well-dispersed nanocomposite films were prepared by optimizing the BST nanoparticle size sorting process (ultrasound crushing and centrifuge method). The size-sorted BST nanoparticles (∼30nm in size) were homogeneously mixed in the PVP host polymer in various BST contents, from 0 to 70wt%, to tune the dielectric constant (κ) of the resulting nanocomposite films. The composite films exhibit three-fold increase in the κ value from 3.9 to 11.3. The physical properties including leakage current and surface roughness of the composites were also measured as a function of the BST loading content and particle dispersion. The relationship between these properties and the electrical performance of the corresponding organic thin film transistor were explored. Graphical abstract

Effect of high conductivity amorphous InGaZnO active layer on the field effect mobility improvement of thin film transistors

High mobility thin film transistors (TFTs) with a high conductivity amorphous InGaZnO (a-IGZO) active layer were successfully fabricated. The operation of the high-carrier-IGZO thin film transistor with a Schottky barrier (SB) was proposed and clearly experimentally explained. The switching characteristic of SB-TFT does not rely on the accumulation process but due to the Schottky barrier height control. Leakage current can be reduced by Schottky contact at the source/drain (S/D), while it was as high as the on current so that the switch properties could not achieve in ohmic ones. The a-IGZO SB-TFTs with Ag S/D contact express the high performance with μFE of 20.4 cm2 V−1 s−1, Vth of 5.8 V, and ION/IOFF of 2 × 107 @ VD = 1V. The introduction of operating mechanism for TFTs using high conductivity a-IGZO promises an expansion study for other active layer materials.

Origin of major donor states in In–Ga–Zn oxide

To clarify the origin of the major donor states in indium gallium zinc oxide (IGZO), we report measurement results and an analysis of several physical properties of IGZO thin films. Specifically, the concentration of H atoms and O vacancies (VO), carrier concentration, and conductivity are investigated by hard X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, thermal desorption spectroscopy, and Hall effect measurements. The results of these experiments suggest that the origin of major donor states is H occupancy of VO sites. Furthermore, we use first-principles calculations to investigate the influence of the coexistence of VO and H in crystalline InGaO3(ZnO)m (m = 1). The results indicate that when H is trapped in VO, a stable complex is created that serves as a shallow-level donor.