Filip Lenrick

High transconductance self-aligned gate-last surface channel In 0.53 Ga 0.47 As MOSFET

In this paper we present a 55 nm gate length In0.53Ga0.47As MOSFET with extrinsic transconductance of 1.9 mS/µm and on-resistance of 199 Ωµm. The self-aligned MOSFET is formed using metalorganic chemical vapor deposition regrowth of highly doped source and drain access regions. The fabricated 140 nm gate length devices shows a low subthreshold swing of 79 mV/decade, which is attributed to the described low temperature gate-last process scheme.

FIB plan and side view cross-sectional TEM sample preparation of nanostructures.

Focused ion beam is a powerful method for cross-sectional transmission electron microscope sample preparation due to being site specific and not limited to certain materials. It has, however, been difficult to apply to many nanostructured materials as they are prone to damage due to extending from the surface. Here we show methods for focused ion beam sample preparation for transmission electron microscopy analysis of such materials, demonstrated on GaAs-GaInP core shell nanowires. We use polymer resin as support and protection and are able to produce cross-sections both perpendicular to and parallel with the substrate surface with minimal damage. Consequently, nanowires grown perpendicular to the substrates could be imaged both in plan and side view, including the nanowire-substrate interface in the latter case. Using the methods presented here we could analyze the faceting and homogeneity of hundreds of adjacent nanowires in a single lamella.

Growth parameter design for homogeneous material composition in ternary GaxIn1-xP nanowires.

Ternary nanowires (NWs) often exhibit varying material composition along the NW growth axis because of different diffusion properties of the precursor molecules. This constitutes a problem for optoelectronic devices for which a homogeneous material composition is most often of importance. Especially, ternary GaInP NWs grown under a constant Ga-In precursor ratio typically show inhomogeneous material composition along the length of the NW due to the complexity of low temperature precursor pyrolysis and relative rates of growth species from gas phase diffusion and surface diffusion that contribute to synthesis of particle-assisted growth. Here, we present the results of a method to overcome this challenge by in situ tuning of the trimethylindium molar fraction during growth of ternary Zn-doped GaInP NWs. The NW material compositions were determined by use of x-ray diffraction, scanning transmission electron microscopy and energy dispersive x-ray spectroscopy and the optical properties by photoluminescence spectroscopy.

Phase Transformation in Radially Merged Wurtzite GaAs Nanowires.

III–V Nanowires (NWs) grown with metal–organic chemical vapor deposition commonly show a polytypic crystal structure, allowing growth of structures not found in the bulk counterpart. In this paper we studied the radial overgrowth of pure wurtzite (WZ) GaAs nanowires and characterized the samples with high resolution X-ray diffraction (XRD) to reveal the crystal structure of the grown material. In particular, we investigated what happens when adjacent WZ NWs radially merge with each other by analyzing the evolution of XRD peaks for different amounts of radial overgrowth and merging. By preparing cross-sectional lamella samples we also analyzed the local crystal structure of partly merged NWs by transmission electron microscopy. Once individual NWs start to merge, the crystal structure of the merged segments is transformed progressively from initial pure WZ to a mixed WZ/ZB structure. The merging process is then modeled using a simple combinatorial approach, which predicts that merging of two or more WZ NWs will result in a mixed crystal structure containing WZ, ZB, and 4H. The existence large and relaxed segments of 4H structure within the merged NWs was confirmed by XRD, allowing us to accurately determine the lattice parameters of GaAs 4H. We compare the measured WZ and 4H unit cells with an ideal tetrahedron and find that both the polytypes are elongated in the c-axis and compressed in the a-axis compared to the geometrically converted cubic ZB unit cell.

High-Frequency Performance of Self-Aligned Gate-Last Surface Channel MOSFET

We have developed a self-aligned L_g = 55 nm In_0.53Ga_0.47As MOSFET incorporating metal-organic chemical vapor deposition regrown n⁺⁺ In_0.53Ga_0.47As source and drain regions, which enables a record low on-resistance of 199 Ωμm. The regrowth process includes an InP support layer, which is later removed selectively to the n⁺⁺ contact layer. This process forms a high-frequency compatible device using a low-complexity fabrication scheme. We report on high-frequency measurements showing f_max of 292 GHz and f_t of 244 GHz. These results are accompanied by modeling of the device, which accounts for the frequency response of gate oxide border traps and impact ionization phenomenon found in narrow band gap FETs. The device also shows a high drive current of 2.0 mA/μm and a high extrinsic transconductance of 1.9 mS/μm. These excellent properties are attributed to the use of a gate-last process, which does not include high temperature or dry-etch processes.

Straight and kinked InAs nanowire growth observed in situ by transmission electron microscopy

AbstractLive observations of growing nanowires using in situ transmission electron microscopy (TEM) is becoming an increasingly important tool for understanding the dynamic processes occurring during nanowire growth. Here we present observations of growing InAs nanowires, which constitute the first reported in situ growth of a In-V compound in a transmission electron microscope. Real time observations of events taking place over longer growth lengths were possible due to the high growth rates of up to 1 nm/s that were achieved. Straight growth (mainly in 〈111〉B directions) was observed at uniform temperature and partial pressure while intentional fluctuations in these conditions caused the nanowires to form kinks and change growth direction. The mechanisms behind the kinking are discussed in detail. In situ observations of nanowire kinking has previously only been reported for nonpolar diamond structure type materials (such as Si), but here we present results for a polar zinc blende structure (InAs). In this study a closed cell with electron and X-ray transparent a-SiN windows was used in a conventional high resolution transmission electron microscope, enabling high resolution imaging and compositional analysis in between the growth periods.

High-Frequency Performance of Self-Aligned Gate-Last Surface Channel In0.53Ga0.47As MOSFET

We have developed a self-aligned L_g = 55 nm In_0.53Ga_0.47As MOSFET incorporating metal-organic chemical vapor deposition regrown n⁺⁺ In_0.53Ga_0.47As source and drain regions, which enables a record low on-resistance of 199 Ωμm. The regrowth process includes an InP support layer, which is later removed selectively to the n⁺⁺ contact layer. This process forms a high-frequency compatible device using a low-complexity fabrication scheme. We report on high-frequency measurements showing f_max of 292 GHz and f_t of 244 GHz. These results are accompanied by modeling of the device, which accounts for the frequency response of gate oxide border traps and impact ionization phenomenon found in narrow band gap FETs. The device also shows a high drive current of 2.0 mA/μm and a high extrinsic transconductance of 1.9 mS/μm. These excellent properties are attributed to the use of a gate-last process, which does not include high temperature or dry-etch processes.

Electron microscopy study of single crystal BaZr0.9Y0.1O3-x films prepared by chemical solution deposition

Single crystal thin films of 10% yttrium doped barium zirconate (BZY10) have been prepared using chemical solution deposition on magnesium oxide substrates and annealed at 800 or 1000 degrees C. A focused ion beam lift out technique was used to prepare thin (< 100 nm) specimens for transmission electron microscopy (TEM) analysis. A variety of TEM based techniques were used for characterization, including high resolution imaging, X-ray energy dispersive spectroscopy and energy filtered TEM. High resolution TEM imaging indicated a high quality single crystal film with an epitaxial cube on cube type interface between BZY10 and MgO. For the sample annealed 1000 degrees C, annular dark field imaging in scanning transmission electron microscopy (STEM) mode showed a layered pattern of lower intensity in the single crystal film. Energy filtered TEM thickness map together with scanning electron microscopy (SEM) indicate the pattern consists of partially repeating voids.

High In-content InGaN nano-pyramids: Tuning crystal homogeneity by optimized nucleation of GaN seeds

Uniform arrays of submicron hexagonal InGaN pyramids with high morphological and material homogeneity, reaching an indium composition of 20%, are presented in this work. The pyramids were grown by selective area metal-organic vapor phase epitaxy and nucleated from small openings in a SiN mask. The growth selectivity was accurately controlled with diffusion lengths of the gallium and indium species, more than 1 μm on the SiN surface. High material homogeneity of the pyramids was achieved by inserting a precisely formed GaN pyramidal seed prior to InGaN growth, leading to the growth of well-shaped InGaN pyramids delimited by six equivalent 10 1 ¯ 1 facets. Further analysis reveals a variation in the indium composition to be mediated by competing InGaN growth on two types of crystal planes, 10 1 ¯ 1 and (0001). Typically, the InGaN growth on 10 1 ¯ 1 planes is much slower than on the (0001) plane. The formation of the (0001) plane and the growth of InGaN on it were found to be dependent on the morphology of the GaN seeds. We propose growth of InGaN pyramids seeded by 10 1 ¯ 1-faceted GaN pyramids as a mean to avoid InGaN material grown on the otherwise formed (0001) plane, leading to a significant reduction of variations in the indium composition in the InGaN pyramids. The InGaN pyramids in this work can be used as a high-quality template for optoelectronic devices having indium-rich active layers, with a potential of reaching green, yellow, and red emissions for LEDs.Uniform arrays of submicron hexagonal InGaN pyramids with high morphological and material homogeneity, reaching an indium composition of 20%, are presented in this work. The pyramids were grown by selective area metal-organic vapor phase epitaxy and nucleated from small openings in a SiN mask. The growth selectivity was accurately controlled with diffusion lengths of the gallium and indium species, more than 1 μm on the SiN surface. High material homogeneity of the pyramids was achieved by inserting a precisely formed GaN pyramidal seed prior to InGaN growth, leading to the growth of well-shaped InGaN pyramids delimited by six equivalent 10 1 ¯ 1 facets. Further analysis reveals a variation in the indium composition to be mediated by competing InGaN growth on two types of crystal planes, 10 1 ¯ 1 and (0001). Typically, the InGaN growth on 10 1 ¯ 1 planes is much slower than on the (0001) plane. The formation of the (0001) plane and the growth of InGaN on it were found to be dependent ...

High-Frequency Performance of Self-Aligned Gate-Last Surface Channel

We have developed a self-aligned L_g = 55 nm In_0.53Ga_0.47As MOSFET incorporating metal-organic chemical vapor deposition regrown n⁺⁺ In_0.53Ga_0.47As source and drain regions, which enables a record low on-resistance of 199 Ωμm. The regrowth process includes an InP support layer, which is later removed selectively to the n⁺⁺ contact layer. This process forms a high-frequency compatible device using a low-complexity fabrication scheme. We report on high-frequency measurements showing f_max of 292 GHz and f_t of 244 GHz. These results are accompanied by modeling of the device, which accounts for the frequency response of gate oxide border traps and impact ionization phenomenon found in narrow band gap FETs. The device also shows a high drive current of 2.0 mA/μm and a high extrinsic transconductance of 1.9 mS/μm. These excellent properties are attributed to the use of a gate-last process, which does not include high temperature or dry-etch processes.