Nitride Si Research Articles

Enhanced optical Kerr nonlinearity of graphene/Si hybrid waveguide

In this work, we experimentally study the optical Kerr nonlinearities of graphene/Si hybrid waveguides with enhanced self-phase modulation. In the case of CMOS compatible materials for nonlinear optical signal processing, Si and silicon nitride waveguides have been extensively investigated over the past decade. However, Si waveguides exhibit strong two-photon absorption (TPA) at telecommunication wavelengths, which leads to a significant reduction of the nonlinear figure-of-merit (FOM). In contrast, a silicon nitride based material system usually suppresses the TPA but simultaneously leads to the reduction of Kerr nonlinearity by one order of magnitude. Here, we introduce a graphene/Si hybrid waveguide, which maintains the optical properties and CMOS compatibility of Si waveguides, while enhancing the Kerr nonlinearity, by transferring over to the top of the waveguides. The graphene/Si waveguides are measured to have an enhanced nonlinear parameter of 510 W−1 m−1, compared with that of the Si waveguide of 150 W−1 m−1. An enhanced nonlinear FOM of 2.48 ± 0.25 has been achieved, which is four times larger than that of the Si waveguide of 0.6 ± 0.1. This work reveals the potential application of graphene/Si hybrid waveguides with high Kerr nonlinearity and FOM for nonlinear all-optical signal processing.

Ultralow-power chip-based soliton microcombs for photonic integration

The generation of dissipative Kerr solitons in optical microresonators has provided a route to compact frequency combs of high repetition rate, which have already been employed for optical frequency synthesizers, ultrafast ranging, coherent telecommunication and dual-comb spectroscopy. Silicon nitride (Si$_3$N$_4$) microresonators are promising for photonic integrated soliton microcombs. Yet to date, soliton formation in Si$_3$N$_4$ microresonators at electronically detectable repetition rates, typically less than 100 GHz, is hindered by the requirement of external power amplifiers, due to the low quality ($Q$) factors, as well as by thermal effects which necessitate the use of frequency agile lasers to access the soliton state. These requirements complicate future photonic integration, heterogeneous or hybrid, of soliton microcomb devices based on Si$_3$N$_4$ microresonators with other active or passive components. Here, using the photonic Damascene reflow process, we demonstrate ultralow-power single soliton formation in high-Q ($Q_0>15\times10^6$) Si$_3$N$_4$ microresonators with 9.8 mW input power (6.2 mW in the waveguide) for devices of electronically detectable, 99 GHz repetition rate. We show that solitons can be accessed via simple, slow laser piezo tuning, in many resonances in the same sample. These power levels are compatible with current silicon-photonics-based lasers for full photonic integration of soliton microcombs, at repetition rates suitable for applications such as ultrafast ranging and coherent communication. Our results show the technological readiness of Si$_3$N$_4$ optical waveguides for future all-on-chip soliton microcomb devices.

Permanent mitigation of loss in ultrathin silicon-on-insulator high-Q resonators using ultraviolet light

In this paper, we demonstrate strip-loaded guiding optical components realized on a 27 nm ultra-thin SOI platform. The absence of physically etched boundaries within the guiding core suppresses majorly the scattering loss, as shown by us previously for a silicon nitride (Si$_3$N$_4$) platform [Stefan \textit{et. al.}, OL 40, 3316 (2015)]. Unexpectedly, the freshly fabricated Si devices showed large losses of 5 dB/cm, originating from absorption by free carriers, accumulated under the positively charged Si$_3$N$_4$ loading layer. We use 254 nm ultraviolet (UV) light exposures to neutralize progressively and permanently silicon nitride's bulk charge associated with diamagnetic K+defects. This in turn leads to a net decrease of electron concentration in the SOI layer, reducing thus the propagation loss down to 0.9 dB/cm. Detailed MOS-capacitance measurements on test samples were performed to monitor the UV-induced modification of the electronic properties of the system. The evolution of loss mitigation was directly monitored both by Beer-Lambert approach in waveguide transmission experiments, as well as through more accurate cavity linewidth measurements. In the last case, we demonstrate how intrinsic cavity $Q$'s boost from 60,0000 to up to 500,000 after UV treatment. Our results may open routes towards engineering of new functionalities in photonic devices employing UV-modification of space charges and associated local electric fields, unveil the origin of induced optical nonlinearities in Si$_3$N$_4$/Si micro-photonic systems, as well as envisage possible integration of these with ultra-thin SOI electronics.

Silicon nitride as antireflection coating to enhance the conversion efficiency of silicon solar cells

The aim of this work is to investigate the effect of single and double layer antireflection coating (ARC) on the performance of silicon solar cells. In this regard, various previous works on single and double layer ARCs have been consulted. Silicon nitride (Si 3 N 4 ) has been used as ARC material because of its varying refractive index (1.8-3.0). Numerical calculations have been performed to obtain the reflectance for single and double layer Si 3 N 4 using the transfer matrix method. Double layer antireflection coating (DLARC) of Si 3 N 4 is found to have significant advantages over single layer antireflection coating (SLARC). Calculated reflectances have been further used in the PC1D simulator as external reflectance files to study the performance of a silicon solar cell. As a result of the simulation, the reflectance is found to reduce from >30% to <2% with short circuit current of 3.86 mA/cm 2 and conversion efficiency of 20.22% for DLARC. Results obtained for DLARC were further compared with a reference cell (without ARC), a cell with SLARC, and a cell with zero reflectance on the front surface.

266-nm ps Laser Ablation for Copper-Plated p-Type Selective Emitter PERC Silicon Solar Cells

Application of 266-nm picosecond (ps) laser ablation and copper (Cu)-plated metallization to p-type selective emitter (SE) passivated emitter and rear cells (PERC) is reported in this paper. Use of a 266-nm ps laser resulted in similar laser-induced periodic surface structures as observed for 355-nm ps laser ablation of a silicon (Si) nitride antireflection coating (ARC) on random-textured Si solar cell surfaces. In addition, it is shown that 266-nm ps laser ablation results in the formation of amorphous Si with an underlying distorted crystalline Si layer at the laser-ablated surfaces. The successful alignment of laser-ablated openings to the heavily doped SE regions resulted in a comparable cell efficiency of Cu-plated SE PERC cells to screen-printed controls, with a maximum cell efficiency of 20.6% being achieved for the Cu-plated cells. The plated cell performance was limited by the recombination losses, and in particular nonideal recombination caused by the use of a shallow emitter, which had been optimized for screen-printed metallization. Engineering of an SE with a junction depth of 0.52 μ m in the heavily doped regions resulted in a 0.3% absolute increase in pseudo fill factor and demonstrated the importance of displacing the p-n junction from the laser-ablated Si surface. Although 355-nm ps laser ablation has been demonstrated to result in strong busbar adhesion in previous reports of Cu-plated cells, significant variability in the busbar adhesion of the fully plated SE PERC cells resulted by 266-nm ps laser ablation. The predicted increased sensitivity of 266-nm laser ablation to the ARC thickness and the possibility that surface oxides were not uniformly removed across wafers before plating may have affected the uniformity of silicide formation and hence the adhesion of the plated busbars.

Passivation effect of ultra-thin SiNx films formed by catalytic chemical vapor deposition for crystalline silicon surface

We propose a way of replacing silicon dioxide (SiO2) films in tunnel oxide passivated contact (TOPCon) solar cells by ultra-thin Si nitride (SiNx) films. We deposit SiNx films on n-type crystalline Si (c-Si) wafers by catalytic chemical vapor deposition (Cat-CVD), by which we avoid a plasma damage to the surface of c-Si. Thin (<5 nm) SiNx films can be deposited with good controllability by tuning the deposition conditions. To improve the passivation quality of SiNx films, hydrogen treatment was performed onto the SiNx-coated c-Si surfaces. Their effective minority carrier lifetime (τeff) can be improved up to >1 ms by the hydrogen treatment for the samples containing SiNx with a proper refractive indices and >10-nm-thick n-type amorphous Si (n-a-Si). The ultra-thin SiNx films have sufficiently high passivation ability and have the required level for the passivation layers of rear-side contact in the TOPCon-like c-Si solar cells.

Graphene Stress Transducer-Based Thermo-Mechanically Fractured Micro Valve

This paper presents the design, analysis, and testing of a single-shot thermo-mechanically triggered micromachined micro-valve with graphene on a silicon nitride (Si x N y ) membrane. The graphene serves as a 2-D resistive heater for producing thermo-mechanical stress, to fracture the bilayer formed between nitride and the nickel used to make electrodes. It is demonstrated that the ability of graphene to carry much higher current density per unit than metal heaters enables high thermo-mechanical stress to be generated. The valve is demonstrated as an enabling component of polymer substrate-based vaporizable electronics. It is used for sealing rubidium (Rb) in polymer chambers, and then triggering and exposing it to ambient air to produce heat by exothermic oxidation. This heat energy is used to vaporize the polymers. The nominal valve tested in this work is a $750\,\,\mu \text{m}\,\,\times 750\,\,\mu \text{m}$ membrane of Si x N y . An analytical and finite-element model are presented for the valve, which agree with measured membrane peak-to-peak deflection of $4.1~\mu \text{m}$ just before fracturing, and a peak fracture stress of 395 MPa. The pulsed-power for triggering the valve is nominally 142.1 ± 13.5 mW with a trigger time of 15.4 ± 3.9 ms, resulting in a very low input trigger energy of 2.2 mJ. This trigger energy is $100\times $ lower compared with that of previously reported single-use valves in the literature. [2017–0317]

Imaging of immunogold labeling in cells and tissues by helium ion microscopy.

Helium ion microscopy (HIM) scans samples with a fine ion beam exploiting the very short de Broglie wavelength of helium ions. Because the radiation induces only a small sample region to emit secondary electrons (SEs), very high resolution is expected. In order to explore the applications of SE-HIM in biology, COS7 kidney fibroblast cells and C2C12 myoblast cells cultured on a silicon (Si) nitride (SiN)/Si bilayer were dried and directly observed in high vacuum, without coating or staining. High contrast, high depth-of-field images were obtained revealing the nucleus, endoplasmic reticulum, cytoskeleton and putative mitochondria above a bright background from the support. Gold-tagged antibodies were employed to aid organelle identification. Signals from the gold tags were most clearly distinguishable by secondary electron (SE)-HIM when cells were grown on thin SiN film, and the minimum gap measured between gold particles showed the resolution to be 2 nm. Wheat germ agglutinin-gold labeling revealed clusters of gold particles ~50–200 nm in diameter on COS7 cells, which might represent assemblies of glycosylated proteins, suggesting the formation of membrane raft structures that include membrane proteins. SE-HIM also delivered high contrast images of unstained, uncoated, thin sections of Epon-embedded mouse kidney tissues mounted on a SiN/Si bilayer, revealing the details of sub-tissues and cell organelles. A charge-coupled mechanism explaining the observed SE-HIM contrast is proposed. Ionoluminescence-HIM was also performed targeting zinc oxide particles on cells. In conclusion, the high depth-of-field, high-resolution imaging achieved using HIM may have applications in various fields, including soft materials.

Multistage performance deterioration in n-type crystalline silicon photovoltaic modules undergoing potential-induced degradation

This study addresses the behavior of n-type front-emitter (FE) crystalline-silicon (c-Si) photovoltaic (PV) modules in potential-induced degradation (PID) tests with a long duration of up to 20 days. By PID tests where a negative bias of −1000 V was applied at 85 °C to 20 × 20-mm2-sized n-type FE c-Si PV cells in modules, the short-circuit current density (Jsc) and the open-circuit voltage (Voc) started to be decreased within 10 s, and strongly saturates within approximately 120 s, resulting in a reduction in the maximum output power (Pmax) and its saturation. After the saturation, all the parameters were almost unchanged until after 1 h. However, the fill factor (FF) then started to decrease and saturated again. After approximately 48 h, FF further decreased again, accompanied by a reduction in Voc. The first degradation is known to be due to an increase in the surface recombination of minority carriers by the accumulation of additional positive charges in the front Si nitride (SiNx) films. The second and third degradations may be due to significant increases in recombination in the space charge region. The enhancement in recombination in the space charge region may be due to additional defect levels of sodium (Na) introduced into the space charge region in the p–n junction. We also performed recovery tests by applying a positive bias of +1000 V. The module with the first degradation completely recovered its performance losses, and the module with the second degradation was almost completely recovered. On the contrary, the modules with the third degradation could not be recovered. These findings may improve the understanding of the reliability of n-type FE c-Si PV modules in large-scale PV systems.

Structural, chemical and optical properties of cerium dioxide film prepared by atomic layer deposition on TiN and Si substrates

Thin films of cerium dioxide (CeO2) were deposited by atomic layer deposition (ALD) at 250°C on both Si and titanium nitride (TiN) substrates. The ALD growth produces CeO2 films with polycrystalline cubic phase on both substrates. However, the films show a preferential orientation along 〈200〉 crystallographic direction for CeO2/Si or 〈111〉 for CeO2/TiN, as revealed by X-ray diffraction. Additionally, CeO2 films differ in the interface roughness depending on the substrate. Furthermore, the relative concentration of Ce3+ is 22.0% in CeO2/Si and around 18% in CeO2/TiN, as obtained by X-ray photoelectron spectroscopy (XPS). Such values indicate a ~10% off-stoichiometry and are indicative of the presence of oxygen vacancies in the films. Nonetheless, CeO2 bandgap energy and refractive index at 550nm are 3.54±0.63eV and 2.3 for CeO2/Si, and 3.63±0.18eV and 2.4 for CeO2/TiN, respectively. Our results extend the knowledge on the structural and chemical properties of ALD-deposited CeO2 either on Si or TiN substrates, underlying films differences and similarities, thus contributing to boost the use of CeO2 through ALD deposition as foreseen in a wide number of applications.

Thermomechanical Adhesion between Metallic Glass and Die Materials

Thermoplastic forming is a promising method for fabricating metallic glass (MG) products with complex shapes. This method can avoid the difficulties encountered in other manufacturing processes, such as very high cooling rate required by casting and catastrophic cracking in machining. However, during thermoplastic forming the adhesion between dies and MGs restricts the production. It is therefore important to explore the underlying adhesion mechanisms during forming and establish guidelines for selecting proper die materials. In this paper, we comprehensively studied the adhesion between La-based MG and some widely-used die materials (electroless Ni-P, Si, alumina and silicon nitride) in the thermoplastic forming process. It was found that, among these die materials, alumina has the best performance, which is attributed to its strong chemical bonds and low surface energy. The study concludes that the surface energy and the type of chemical bonds can be proper indicators for selecting die materials.

Compositional and Structural Atomistic Study of Amorphous Si–B–N Networks of Interest for High-Performance Coatings

We explore by computational modeling the effects of boron–nitrogen (BN) composition on the thermal and mechanical properties of amorphous silicon–boron–nitride (Si–B–N), a synthetic ceramic material with superior thermal protection, mechanical attributes, and oxidation resistance at high temperatures. Network-derived Si–B–N models optimized with ab initio molecular dynamics serve as input structures for classical molecular dynamics simulations. Atomistic Green–Kubo simulations on relaxed supercells and structural relaxations on strained cells are used to screen the thermal and mechanical properties of a collection of network structures with low enthalpies of formation. We find that when the material is composed of well-mixed parts rather homogeneously spread within the material, the thermal conductivity and elastic constants are isotropic and exhibit a weak dependence on composition and network structure. In contrast, when separation into BN-rich layers occurs, the material exhibits anisotropic behavior, ...

Structural and mechanical evolution of TiAlSiN nanocomposite coating under influence of Si3N4 power

Abstract In this study, we have reported the microstructural and mechanical properties of nanocrystalline Titanium Aluminum Nitride (TiAlN) embedded in amorphous Silicon Nitride (Si 3 N 4 ) nanocomposite films. The films were deposited on Si substrate by using DC\RF reactive magnetron co-sputtering of TiAl and Si 3 N 4 targets by varying power to the Si 3 N 4 target. The films were investigated using grazing incident X-ray diffraction (GIXRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), stylus profiler and nanoindentation. GIXRD shows the formation of crystalline cubic Ti 3 AlN phase in the films. With the increase in Si 3 N 4 power, crystal growth of TiAlN diminishes. FESEM micrographs showed the uniformly distributed, well developed, sharp-edged, irregular shaped grains on the surface of the films. The silicon-rich region was observed at inter-grain boundary region and the micrographs visualize the presence of amorphous Si 3 N 4 on the edge of crystal grains. The amorphous content increases with Si 3 N 4 power. EDS confirms the presence of all elements in the films. The optimum mechanical properties were observed at 70 W Si 3 N 4 target power. Hardness, elastic modulus, elastic recovery and resistance to plastic deformation of film rises from 40 W to 70 W target power and then reduces at 90 W.

Influence of Nitrogen Environment on the Surface of LM25 using GTA

Objective: The main aim of this project is to modify the surface of LM 25 ingot in order to have a refined microstructure, improvement in hardness and in the wear rate of the modified region. Methods: Surface modification of LM 25 is carried out using GTA method. Argon flow was minimised and simultaneously pure nitrogen (99.999%) was introduced into the environment. Microstructural observation was carried out using Zeiss Axiovert 25CA metallurgical microscope and the hardness was measured using Mitutoyo Vicker’s hardness testing machine. Wear test was carried out for the substrate and the modified region using pin-on-disc wear tester. EDAX analysis was carried out to find the presence of intermetalic compounds. Findings: From the microstructure, it was observed that there is grain refinement in the modified region. The hardness for the substrate was found to be 80.6 HV and 764.4 HV for the modified region. The wear rate in the substrate was 49.34x10 -4 mm 3 /m and 7.9x10 -4 mm 3 /m for the modified region. As the hardness increases, wear rate decreases. EDAX report confirms the presence of intermetalic compound in the form of silicon nitride (Si 3 N 4 ). The presence of the silicon nitride is not reported previously using GTA as heat source on surface modified LM25. The increase in the hardness and decrease in the wear rate is attributed to the presence of silicon nitride in the surface. Application/Improvements: Due to the presence of silicon nitride it can be used as an insulator and chemical barrier in electrical circuits etc. It can also have wider automobile and aeronautics applications as its hardness has increased.

Efficiency Improvement by Charged-insulator Layers for IBC-SHJ Cells

A novel approach has been proposed to solve conversion efficiency degradation due to recombination loss at a gap region between p/i- and n/i-aSi:H layers in an interdigitated back contact Si heterojunction (IBC-SHJ) cell architecture. In our approach, a charged-insulator layer is newly introduced to cover the i-aSi:H on the gap region. Our simulation demonstrates that this leads to suppression of the recombination at the gap region, resulting in a significant improvement in the efficiency. Fixed-charge (Qf) with density of around 1012 cm-2 almost fully recovers the efficiency even with a low-quality surface at the gap around with the interfacial defect density of 1012 cm-2eV-1. The decrease in the recombination is owing to the field-effect passivation induced by the Qf. The recovery in the efficiency by Qf still works even though the quantum effects is considered, which causes some modification in the carrier distribution at the hetero-interface. Such charged-insulators are feasible by already existing materials such as Si nitride. In addition, this charged insulator architecture allows easy alignment for the backside structure. Thus, this proposal will be easily adopted for a mass production where the relaxed design rule is mandatory.

Mechanical Resonators for Quantum Optomechanics Experiments at Room Temperature.

All quantum optomechanics experiments to date operate at cryogenic temperatures, imposing severe technical challenges and fundamental constraints. Here, we present a novel design of on-chip mechanical resonators which exhibit fundamental modes with frequencies f and mechanical quality factors Q_{m} sufficient to enter the optomechanical quantum regime at room temperature. We overcome previous limitations by designing ultrathin, high-stress silicon nitride (Si_{3}N_{4}) membranes, with tensile stress in the resonators' clamps close to the ultimate yield strength of the material. By patterning a photonic crystal on the SiN membranes, we observe reflectivities greater than 99%. These on-chip resonators have remarkably low mechanical dissipation, with Q_{m}∼10^{8}, while at the same time exhibiting large reflectivities. This makes them a unique platform for experiments towards the observation of massive quantum behavior at room temperature.

(Invited) High-k Materials and Embedded Nanocrystals for Electronic and Photonic Applications

High-k materials play a major role in semiconductor research and development. Semiconductor industry made a step towards high-k dielectrics like Al2O3, HfO2 and ZrO2 for MIM capacitors in DRAM and rf applications [1], as well as for gate dielectrics for sub 45 nm devices or in high electron mobility transistor in GaN based hetero structures. Implementing high-K materials into the process flow of a GaN based high electron mobility transistor needs to adapt the whole process sequence, like thermal budget of electrode formation etc. [2]. Furthermore, in solar industry the high-k material Al2O3 is discussed to replace SiN passivation layer for the newest PERC concept [3,4]. Beyond the already established applications routes high-k materials show superior properties as matrix material for semiconductor quantum dots – rare earth element alloys to enhance their optical and electrical properties. Embedded group IV nanocrystals like Si and Ge show superior charge storage properties in high-K matrix materials deposited via rf-magnetron sputtering. Ge nanocrystals embedded in an amorphous TaZrOx matrix as blocking oxide implemented in a metal-insulator-semiconductor capacitor show a voltage hysteresis in a capacitance-voltage slope of 5 V and a programming voltage – hysteresis voltage slope of nearly 1 [5]. In case of embedded Au nanoparticles in sol gel deposited Er doped ZrO2 films a temperature stability of the Au nanoparticle related surface plasmon resonance up to 1000°C annealing temperature could be shown [6]. In this contribution we will review our efforts to realize optimized properties of the high-K materials for the needs of the different applications as matrix material for nanocrystalline semiconductors for optical and electrical applications and as passivation layer for Si photovoltaics or nitride electronics. [1] J. Heitmann, A. Avellan, T. Boescke, E. Erben, B. Hintze, S. Jakschik, S. Kudelka, and U. Schroeder, HfAlO and HfSiO Based Dielectrics for Future DRAM Application, ECS. Trans. 2 (2006) 217. [2] Schmid, A.; Schröter, Ch.; Otto, R.; Schuster, M.; Klemm, V.; Rafaja, D.; Heitmann, J., Appl. Phys. Lett. 106, 053509 (2015) [3] Benick et al. Applied Physics Letters 2008; 92; 253504 [4] F. Kersten, A. Schmid, S. Bordihn, J. W. Müller, J. Heitmann, Energy Procedia, 38, p. 843, (2013) [5] D. Lehninger, P. Seidel, M. Geyer, F. Schneider, V. Klemm, D. Rafaja, J. von Borany, J. Heitmann, Appl. Phys. Lett. 106, 023116 (2015) [6] S. Seidel, A. Sabelfeld, R. Strohmeyer, G. Schreiber, V. Klemm, D. Rafaja, Y. Joseph, and J. Heitmann, J. of Appl. Phys., submitted for publication.

Effects of annealing temperatures on the morphological, mechanical, surface chemical bonding, and solar selectivity properties of sputtered TiAlSiN thin films

Quaternary sputtered TiAlSiN coatings were investigated for their high temperature structural stability, surface morphology, mechanical behaviors, surface chemical bonding states, solar absorptance and thermal emittance for possible solar selective surface applications. The TiAlSiN films were synthesized, via unbalanced magnetron sputtered technology, on AISI M2 steel substrate and annealed at 500 °C - 800 °C temperature range. SEM micrographs show nanocomposite-like structure with amorphous grain boundaries. Nanoindentation analyses indicate a decrease of hardness, plastic deformation and constant yield strength for the coatings. XPS analysis show mixed Ti, Al and Si nitride and oxide as main coating components but at 800 °C the top layer of the coatings is clearly composed of only Ti and Al oxides. Synchrotron radiation XRD (SR-XRD) results indicate various Ti, Al and Si nitride and oxide phases, for the above annealing temperature range with a phase change occurring with the Fe component of the substrate. UV–Vis spectroscopy, FTIR spectroscopy studies determined a high solar selectivity, s of 24.6 for the sample annealed at 600 °C. Overall results show good structural and morphological stability of these coatings at temperatures up to 800 °C with a very good solar selectivity for real world applications.

Surface texturing of Si3N4–SiC ceramic tool components by pulsed laser machining

Abstract Traditional abrasive techniques such as grinding and lapping have long been used in the surface conditioning of engineering materials. However, in the processing of hard and brittle materials like silicon nitride (Si 3 N 4 ), machining is often accompanied by numerous shortcomings which either lead to poor surface quality or residual surface damage of the workpiece. In this sense, this work focuses on the application of a pulsed mode, nanosecond Nd:YAG laser system for the surface texturing of Si 3 N 4 –SiC composites in the fabrication of machining tool inserts for various tribological applications. The samples were machined at varied laser energy (0.1–0.6 mJ) and lateral pulse overlap (50–88%) in order to generate a sequence of linear parallel micro-grooves on the sample surfaces. The results showed a logarithmic increase in material removal as pulse energy and lateral overlaps were increased. The material removal threshold was established at 0.1 mJ (0.78 × 10 5 J/m 2 ). Optimum surface texturing was achieved at a combination of 0.3 mJ (2.38 × 10 5 J/m 2 ) and 50%, pulse energy and lateral pulse overlap respectively.

Nitride passivation of the interface between high-k dielectrics and SiGe

In-situ direct ammonia (NH3) plasma nitridation has been used to passivate the Al2O3/SiGe interfaces with Si nitride and oxynitride. X-ray photoelectron spectroscopy of the buried Al2O3/SiGe interface shows that NH3 plasma pre-treatment should be performed at high temperatures (300 °C) to fully prevent Ge nitride and oxynitride formation at the interface and Ge out-diffusion into the oxide. C-V and I-V spectroscopy results show a lower density of interface traps and smaller gate leakage for samples with plasma nitridation at 300 °C.