Henry H. Radamson

Graphene synthesis, characterization and its applications in nanophotonics, nanoelectronics, and nanosensing

AbstractIn the last decade, as semiconductor industry was approaching the end of the exponential Moore’s roadmap for device downscaling, the necessity of finding new candidate materials has forced many research groups to explore many different types of non-conventional materials. Among them, graphene, CNTs and organic conductors are the most successful alternatives. Finding a material with metallic properties combined with field effect characteristics on nanoscale level has been always a dream to continue the ever-shrinking road of the nanoelectronics. Due to its fantastic features such as high mobility, optical transparency, room temperature quantum Hall effect, mechanical stiffness, etc. the atomically thin carbon layer, graphene, has attracted the industry’s attention not only in the micro-, nano-, and opto-electronics but also in biotechnology. This paper reviews the basics and previous works on graphene technology and its developments. Compatibility of this material with Si processing technology is its crucial characteristic for mass production. This study also reviews the physical and electrical properties of graphene as a building block for other carbon allotropes. Different growth methods and a wide range of graphene’s applications will be discussed and compared. A brief comparison on the performance result of different types of devices has also been presented. Until now, the main focus of research has been on the background physics and its application in electronic devices. But, according to the recent works on its applications in photonics and optoelectronics, where it benefits from the combination of its unique optical and electronic properties, even without a bandgap, this material enables ultrawide-band tunability. Here in this article we review different applications and graphene’s advantages and drawbacks will be mentioned to conclude at the end.

Increased nucleation temperature of NiSi2 in the reaction of Ni thin films with Si1−xGex

The formation of a ternary solid solution NiSi1−xGex, instead of a mixture of NiSi and NiGe, is found during solid-state interactions between Ni and various Si1−xGex films ranging from pure Si to pure Ge. The lattice parameters of the solid solution of orthorhombic structure increase linearly with Ge content (x) as: a=5.24+0.19x A, b=3.25+0.16x A, and c=5.68+0.15x A. The specific resistivity increases from 17 μΩ cm for NiSi to 21 μΩ cm for NiSi0.71Ge0.29 and NiSi0.42Ge0.58. Although the Ge content rapidly drops from 30–60 to about 10 at. % in the solid solutions formed above 600 °C, the crystallographic structure remains unchanged and no NiSi2 [or Ni(Si,Ge)2] is found in the Si1−xGex samples even after annealing at 850 °C. Without Ge, the NiSi completely disappears at 750 °C. These results indicate a strong effect of the entropy of mixing in NiSi–NiGe on the nucleation of NiSi2.

Loading effect in SiGe layers grown by dichlorosilane- and silane-based epitaxy

The evolution of the loading effect in Si1-xGex layers (0 less than or equal tox less than or equal to 20%) versus growth parameters has been investigated for selective and nonselective growth usin ...

Morphological instability of NiSi1-uGeu on single-crystal and polycrystalline Si1-xGex

The morphological stability of NiSi1−uGeu ternary alloy films formed by reacting Ni with single-crystal (sc) and polycrystalline (poly) Si1−xGeu is studied (u can be different from x). The agglomeration of NiSi1−uGeu films on Si0.7Ge0.3 occurs at 550°C after rapid thermal processing for 30 s, independently of the crystallinity of the Si1−xGeu. This behavior distinctly different from NiSi: NiSi films on poly-Si display a poorer morphological stability and degrade at lower temperatures than NiSi on sc-Si. On strained Si1−xGex, the presence of Ge simultaneously gives rise to two effects of different origin: mechanical and thermodynamic. The main driving forces behind the agglomeration of NiSi1−uGeu on sc-Si1−xGex are found to be the stored strain energy in the Si1−xGex and the larger (absolute) free energy of formation of NiSi compared to NiGe. The latter constitutes the principal driving force behind the agglomeration of NiSi1−uGeu on poly-Si1−xGex and is not affected by the degree of crystallinity of Si1−x...

Improvement of infrared detection using Ge quantum dots multilayer structure

Monocrystalline SiGe/Si multiquantum dot and well structures have been manufactured/compared as thermistor materials for infrared detection. The performance of the devices (both the thermal and electrical) has been very sensitive to the quality of the epitaxial layers which is evaluated by the interfacial roughness and strain amount. This study demonstrates that the devices containing quantum dots have higher thermal coefficient resistance 3.4%/K with a noise constant (K1/f) value of 2×10−9.

Carbon-doped single-crystalline SiGe/Si thermistor with high temperature coefficient of resistance and low noise level

SiGe (C)/Si(C) multiquantum wells have been studied as a thermistor material for future bolometers. A thermistor material for uncooled Si-based thermal detectors with thermal coefficient of resista ...

Phosphorus and boron diffusion in silicon under equilibrium conditions

The intrinsic diffusion of phosphorus and boron in high-purity epitaxial silicon films has been studied. Phosphorus diffusion in a wide temperature range (810 to 1100 °C) revealed diffusion coefficients with an Arrhenius behavior exhibiting an activation energy of 2.74±0.07 eV and a pre-exponential factor of (8±5)×10−4 cm2/s. In the temperature range of 810 to 1050 °C, boron was found to diffuse with an activation energy of 3.12±0.04 eV and a pre-exponential factor of 0.06±0.02 cm2/s. These results differ from those of many previous studies, but this deviation may to a large extent be attributed to slow transients before equilibrium concentrations of point defects are established at temperatures below ∼1000 °C. Despite a similar diffusion mechanism mediated by Si self-interstitials, P exhibits a lower activation energy than B because of stronger bonding to the Si self-interstitial.

Optimization of SiGe selective epitaxy for source/drain engineering in 22 nm node complementary metal-oxide semiconductor (CMOS)

SiGe has been widely used for source/drain (S/D) engineering in pMOSFETs to enhance channel mobility. In this study, selective Si1−xGex growth (0.25 ≤ x ≤ 0.35) with boron concentration of 1–3 × 1020 cm−3 in the process for 22 nm node complementary metal-oxide semiconductor (CMOS) has been investigated and optimized. The growth parameters were carefully tuned to achieve deposition of high quality and highly strained material. The thermal budget was decreased to 800 °C to suppress dopant diffusion, to minimize Si loss in S/D recesses, and to preserve the S/D recess shape. Two layers of Si1−xGex were deposited: a bottom layer with high Ge content (x = 0.35) which filled the recess and a cap layer with low Ge content (x = 0.25) which was elevated in the S/D regions. The elevated SiGe cap layer was intended to be consumed during the Ni-silicidation process in order to avoid strain reduction in the channel region arising from strain relaxation in SiGe S/D. In this study, a kinetic gas model was also applied to...

Application of high-resolution x-ray diffraction for detecting defects in SiGe(C) materials

The application of high-resolution x-ray diffraction for detecting and distinguishing defects in SiGe(C) layers is presented. A depth profile of the defects in SiGe/Si multilayers has been performed by using high-resolution reciprocal lattice mapping at different asymmetric reflections. Transmission electron microscopy was also applied in order to observe defects in the layers and these results were linked with the x-ray analysis. The substitutional C or B concentration in SiGe was measured by the shift of layer peak compared to the intrinsic layers. The thermal stability of the SiGe layers was investigated in order to rank the epitaxial quality of the SiGe below the detection limit of x-ray technique. It has also been demonstrated that x-ray analysis can be used for in-line process monitoring of layers grown in small device openings on patterned substrates. These types of analysis have also been used routinely for the evaluation of processed samples.

Electron mobility enhancement in Si using doubly δ‐doped layers

Large enhancements in the electron mobility are reported for structures containing a pair of closely spaced Sb δ‐doped layers in Si. The room‐temperature mobility is enhanced by a factor of 2 compared to corresponding uniformly doped layers of singly δ‐doped structures. Even higher mobilities were obtained by using a Schottky gate on top and applying a voltage to adjust the potential well. With an effective gate voltage of ∼−0.3 V the mobility was 1200 cm2 V−1 s−1 at room temperature, which is an enhancement by a factor of 10 relative to the layer with equivalent bulk doping concentration. The high mobility is attributed to wave functions with nodes at the δ‐doped layers.