Ken Cadien

Ultra low density of interfacial traps with mixed thermal and plasma enhanced ALD of high-κ gate dielectrics

Anomalous growth per cycle was observed using in situ ellipsometry during the initial cycles of plasma enhanced atomic layer deposition (ALD) of high-κ dielectrics, while thermal atomic layer deposition of these oxides exhibited linear growth per cycle. The anomalous growth per cycle was attributed to oxidation of the substrate by plasma oxygen. Thermally grown films have a lower capacitance density and higher leakage current but lower density of interfacial traps compared to plasma enhanced grown films. For plasma enhanced films, the leakage current is dominated by direct tunnelling while trap assisted tunnelling seems to be dominant in thermally grown films. Initiating the oxide growth with thermal atomic layer deposition and then switching to the plasma enhanced process protects the substrate surface from plasma oxygen and lowers the density of interfacial traps (Dit). Starting with ten cycles of thermal atomic layer deposition of ZrO2 enhances the capacitance density while decreasing the Dit. The lowest value of Dit was obtained with twenty cycles of thermal atomic layer deposition (1.8 × 1010 cm−2 eV−1). The mid-gap Dit reduces systematically with an increasing number of thermal ALD cycles. Furthermore, the frequency dispersion in accumulation is reduced with an increasing number of thermal ALD cycles up to twenty.

A route to low temperature growth of single crystal GaN on sapphire

Gallium nitride (GaN) is considered one of most important semiconductor materials for the 21st century due to its combination of properties (high breakdown field, high electron saturation velocity and mobility, and good thermal conductivity) that make it suitable for high power, high frequency and high temperature applications. In this paper we demonstrate a possible route for the deposition of single crystal GaN on sapphire at 275 °C using plasma enhanced atomic layer deposition. TEM images and electron diffraction show that the first 5 nm of growth is epitaxial then transitions to 3D growth. The films have a preferential (002) growth direction, and a small in-plane and out-of-plane misorientation. The refractive index, extinction coefficient, and optical band gap are on par with those of GaN films grown at higher temperatures. The films are p-type with a carrier concentration of 1.68 × 1018 cm−3 and hole mobility of 110 cm2 V−1 s−1.

Structure–property relationship and interfacial phenomena in GaN grown on C-plane sapphire via plasma-enhanced atomic layer deposition

Gallium nitride films were deposited via plasma-enhanced atomic layer deposition (PEALD) using triethylgallium and forming gas as precursors. An optimized process was developed and the effect of growth temperature on the structure and optical properties of the films investigated. In-depth X-ray diffraction analyses show that there is a critical temperature, below which the films are amorphous. Raising the growth temperature above the critical temperature increases the grain size of the polycrystalline film, while degrading the degree of preferred orientation. Azimuthal XRD scans show clear signs of a crystallographic relationship between the (002) planes of the sapphire substrate and GaN. Growth rate shows a steady rise until a rapid jump at 425 °C occurs. The study of the surface profile by AFM shows that the hillocks on the surface start to grow in diameter as well as height, increasing the total growth front area. This also decreases the surface roughness. XRR studies reveal that mass density reaches its maximum value at 240 °C, and is stable after that. Carrier mobility is increased by two orders of magnitude, when the growth temperature is raised from 150 °C to 425 °C. As expected, a similar but reverse trend was observed for the electrical resistivity. Refractive index follows the trends of mass density and crystal quality with a clear increase at the onset of crystallinity. Overall, the surface profile and the engineering properties improve as growth temperature is increased. At the high end of the growth temperature range, PEALD GaN films grown on (002) sapphire were p-type with a hole mobility of 575 cm2 V−1 s−1.

Electrical Comparison of

A low-temperature atomic layer deposition technique for high-κ dielectric films on GaN templates was investigated for MOS applications. This improved growth method produced capacitance densities and a field effect mobility approaching 375 cm2/Vs for ZrO2 and 250 cm2/Vs for HfO2 films on GaN. Furthermore, the low density of dielectric-semiconductor interface traps confirmed a reliable cohesion between the high-κ and GaN. The improved gate dielectric deposition technique has the capabilities to improve the overall quality of GaN-based MOSFETs.

{\rm HfO}_{2}

Nanocellulose is a sustainable and eco-friendly nanomaterial derived from renewable biomass. In this study, we utilized the structural advantages of two types of nanocellulose and fabricated freestanding carbonized hybrid nanocellulose films as electrode materials for supercapacitors. The long cellulose nanofibrils (CNFs) formed a macroporous framework, and the short cellulose nanocrystals were assembled around the CNF framework and generated micro/mesopores. This two-level hierarchical porous structure was successfully preserved during carbonization because of a thin atomic layer deposited (ALD) Al2O3 conformal coating, which effectively prevented the aggregation of nanocellulose. These carbonized, partially graphitized nanocellulose fibers were interconnected, forming an integrated and highly conductive network with a large specific surface area of 1,244 m2·g–1. The two-level hierarchical porous structure facilitated fast ion transport in the film. When tested as an electrode material with a high mass loading of 4 mg·cm–2 for supercapacitors, the hierarchical porous carbon film derived from hybrid nanocellulose exhibited a specific capacitance of 170 F·g–1 and extraordinary performance at high current densities. Even at a very high current of 50 A·g–1, it retained 65% of its original specific capacitance, which makes it a promising electrode material for high-power applications.

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This paper presents a capacitance model and mobility extraction method through the use of tapered transmission line theory for accumulation-mode MOSCAP test structures. The analytical model accounts for the discrepancies commonly found when measuring the capacitance of nontraditional MOSCAP architectures. Through fabrication of a planar MOSCAP, this model accurately reproduced consistent capacitance density measurements for several device dimensions and high-κ dielectric thicknesses. In this paper, the theoretical basis of the model extracts the effective electron mobility of the accumulation channel in the semiconductor without fabricating a transistor.

{\rm ZrO}_{2}

ZrO2 has been deposited on GaN by Atomic Layer Deposition. Multiple Metal-Oxide-Semiconductor Capacitors with 4.4 nm, 5.4 nm, and 8.5 nm of ZrO2 oxide were fabricated with Cr electrodes. Capacitance measurements produce capacitance densities as high as 3.8 μF/cm2. Current densities of 0.88 A/cm2 at 1 V for the 4.4 nm oxides and hysteresis values of less than 6 mV were observed for the 5.8 nm oxide, indicating an interfacial Dit not greater than 6.4 × 1010 cm2. Temperature dependent current measurements revealed no signature Poole-Frankel component. Comprehensive assessment of these measurements indicates a low defect density oxide formed on GaN with a low number of interface states.

Gate Dielectrics on GaN

There is a great interest in various branches of the advanced materials industry for the development of novel methods (and improvements to existing ones) for the deposition of conformal ultrathin metallic films. In most of these applications, like enhanced solar absorbers and microelectronics, achieving the capacity to deposit a conformal thin film on a three-dimensional structure is an important condition. Plasma-enhanced atomic layer deposition (ALD) is known for its potential for growth of conformal thin films with a precise control over the thickness and its capability for deposition at relatively low temperatures (below 500 °C). This study evaluates the potential of plasma-enhanced ALD for growth of conformal nickel thin films, using bis(ethylcyclopentadienyl)nickel and nitrogen/hydrogen plasma as precursors. A comprehensive analysis of the structure, composition, and physical properties of the films was performed. The results indicate that conformal nickel films with low levels of impurity were successfully deposited on sapphire. The films had a roughness of Ra = 1.5 nm and were seen to be under strain. The deposited nickel had a hexagonal crystal structure, with a random in-plane orientation of the grains, while the grains had their c-axes oriented along the normal to the interface. These results pave the way for conformal low-temperature deposition of high-quality nickel thin films on three-dimensional structures.

Freestanding hierarchical porous carbon film derived from hybrid nanocellulose for high-power supercapacitors

We introduce a new lift-off technique, which, compared to the conventional lift-off process, has both high yield (>;90%) and high reproducibility (>;95%). It has been shown that by etching after pattern transfer and prior to material deposition, the adhesion of the deposited material to the substrate is improved and roughness of feature edges is eliminated. This procedure is tailored to meet fabrication reproducibility criteria for nanoscale as well as microscale features.

Capacitance Modeling and Characterization of Planar MOSCAP Devices for Wideband-Gap Semiconductors With High-

Zinc oxide (ZnO) based materials have attracted much attentions in the past decades for potential utilizations in transparent conducting oxides (TCOs), thin film transistors (TFTs) and light emitting diodes (LEDs) due to its superior properties such as large bandgap (3.37eV), large exciton binding energy (60 meV), high transparency and capability of synthesis under low to intermedium temperature. ZnO thin films are capable to grow on various substrates such as glasses, polymer, and sapphire under low deposition temperature, which makes it attractive in flexible electronics. Schottky contacts for ZnO thin film is an essential study for further applications of this material in photodetector and TFTs. Transparent ZnO based TFTs has become one of the most advance topics for device application currently as one of the most promising technologies leading in the next generation of display. The display market forecast has predicted that transparent display is expected to overtake Flat Panel Display in the next decade1.