SiCILIA-Silicon Carbide Detectors for Intense Luminosity Investigations and Applications.

Silicon carbide (SiC) is a compound semiconductor, which is considered as a possible alternative to silicon for particles and photons detection. Its characteristics make it very promising for the next generation of nuclear and particle physics experiments at high beam luminosity. Silicon Carbide detectors for Intense Luminosity Investigations and Applications (SiCILIA) is a project starting as a collaboration between the Italian National Institute of Nuclear Physics (INFN) and IMM-CNR, aiming at the realization of innovative detection systems based on SiC. In this paper, we discuss the main features of silicon carbide as a material and its potential application in the field of particles and photons detectors, the project structure and the strategies used for the prototype realization, and the first results concerning prototype production and their performance.

Impact of Nitrogen on the Selective Closure of Stacking Faults in 3C-SiC.

Despite the promising properties, the problem of cubic silicon carbide (3C-SiC) heteroepitaxy on silicon has not yet been resolved and its use in microelectronics is limited by the presence of extensive defects. In this paper, we used microphotoluminescence (µ-PL), molten KOH etching, and high-resolution scanning transmission electron microscopy (HRSTEM) to investigate the effect of nitrogen doping on the distribution of stacking faults (SFs) and assess how increasing dosages of nitrogen during chemical vapor deposition (CVD) growth inhibits the development of SFs. An innovative angle-resolved SEM observation approach of molten KOH-etched samples resulted in detailed statistics on the density of the different types of defects as a function of the growth thickness of 3C-SiC free-standing samples with varied levels of nitrogen doping. Moreover, we proceeded to shed light on defects revealed by a diamond-shaped pit. In the past, they were conventionally associated with dislocations (Ds) due to what happens in 4H-SiC, where the formation of pits is always linked with the presence of Ds. In this work, the supposed Ds were observed at high magnification (by HRSTEM), demonstrating that principally they are partial dislocations (PDs) that delimit an SF, whose development and propagation are suppressed by the presence of nitrogen. These results were compared with VESTA simulations, which allowed to simulate the 3C-SiC lattice to design two 3C-lattice domains delimited by different types of SFs. In addition, through previous experimental evidence, a preferential impact of nitrogen on the closure of 6H-like SFs was observed as compared to 4H-like SFs.

Opioids in advanced cancer: use, storage and disposal in the home.

OBJECTIVES: To determine the patterns of storing, using and disposing of opioids among patients with advanced cancer followed at home. METHODS: Patients who were prescribed opioids were selected. Prescribed opioids and their doses used for background pain and breakthrough pain were collected, as well as CAGE (cut down, annoyed, guilty and eye opener) for alcohol and drugs, smoking and history of illicit substance use. Questions regarding the opioid use, storage and disposal were posed. RESULTS: 100 patients were surveyed. Fifty-one patients had unused opioids at home, 25 patients did not throw away the drugs, 40 patients saved opioids for future use and 35 patients were unaware of proper opioid disposal methods. A total of 28 patients reported unsafe use by sharing or losing their opioids; 12 patients were unaware that their opioid could be fatal when taken by others. Most patients acknowledged that pain medications could be dangerous when taken by others. Patients with a partner and who were married were more likely to keep their opioids locked (p=0.028 and p=0.025, respectively). CONCLUSION: A large number of patients with advanced cancer followed at home do not store, use and dispose of opioids safely. Patient education programmes should be incorporated to decrease the availability of opioids at home for abuse, diversion, and accidental poisoning.

Effect of Nitrogen and Aluminum Doping on 3C-SiC Heteroepitaxial Layers Grown on 4° Off-Axis Si (100).

This work provides a comprehensive investigation of nitrogen and aluminum doping and its consequences for the physical properties of 3C-SiC. Free-standing 3C-SiC heteroepitaxial layers, intentionally doped with nitrogen or aluminum, were grown on Si (100) substrate with different 4° off-axis in a horizontal hot-wall chemical vapor deposition (CVD) reactor. The Si substrate was melted inside the CVD chamber, followed by the growth process. Micro-Raman, photoluminescence (PL) and stacking fault evaluation through molten KOH etching were performed on different doped samples. Then, the role of the doping and of the cut angle on the quality, density and length distribution of the stacking faults was studied, in order to estimate the influence of N and Al incorporation on the morphological and optical properties of the material. In particular, for both types of doping, it was observed that as the dopant concentration increased, the average length of the stacking faults (SFs) increased and their density decreased.

New Approaches and Understandings in the Growth of Cubic Silicon Carbide.

In this review paper, several new approaches about the 3C-SiC growth are been presented. In fact, despite the long research activity on 3C-SiC, no devices with good electrical characteristics have been obtained due to the high defect density and high level of stress. To overcome these problems, two different approaches have been used in the last years. From one side, several compliance substrates have been used to try to reduce both the defects and stress, while from another side, the first bulk growth has been performed to try to improve the quality of this material with respect to the heteroepitaxial one. From all these studies, a new understanding of the material defects has been obtained, as well as regarding all the interactions between defects and several growth parameters. This new knowledge will be the basis to solve the main issue of the 3C-SiC growth and reach the goal to obtain a material with low defects and low stress that would allow for realizing devices with extremely interesting characteristics.

Characterization of 4H- and 6H-Like Stacking Faults in Cross Section of 3C-SiC Epitaxial Layer by Room-Temperature µ-Photoluminescence and µ-Raman Analysis.

We report a comprehensive investigation on stacking faults (SFs) in the 3C-SiC cross-section epilayer. 3C-SiC growth was performed in a horizontal hot-wall chemical vapour deposition (CVD) reactor. After the growth (85 microns thick), the silicon substrate was completely melted inside the CVD chamber, obtaining free-standing 4 inch wafers. A structural characterization and distribution of SFs was performed by µ-Raman spectroscopy and room-temperature µ-photoluminescence. Two kinds of SFs, 4H-like and 6H-like, were identified near the removed silicon interface. Each kind of SFs shows a characteristic photoluminescence emission of the 4H-SiC and 6H-SiC located at 393 and 425 nm, respectively. 4H-like and 6H-like SFs show different distribution along film thickness. The reported results were discussed in relation with the experimental data and theoretical models present in the literature.

Growth of Large-Area, Stress-Free, and Bulk-Like 3C-SiC (100) Using 3C-SiC-on-Si in Vapor Phase Growth.

We report on the reproducible growth of two inch 3C-SiC crystals using the transfer of chemical vapor deposition (CVD)-grown (100) oriented epitaxial layers. Additional experiments, in which the diameter of the free-standing layers is increased, are presented, indicating the upscale potential of this process. The nucleation and growth of cubic silicon carbide is supported by XRD and Raman measurements. The rocking curve data yield a full-width-at-half-maximum (FWHM) between 138 to 140 arc sec for such grown material. Analysis of the inbuilt stress of the bulk-like material shows no indications of any residual stress.

Limitations during Vapor Phase Growth of Bulk (100) 3C-SiC Using 3C-SiC-on-SiC Seeding Stacks.

The growth of 3C-SiC shows technological challenges, such as high supersaturation, a silicon-rich gas phase and a high vertical temperature gradient. We have developed a transfer method creating high-quality 3C-SiC-on-SiC (100) seeding stacks, suitable for use in sublimation "sandwich" epitaxy (SE). This work presents simulation data on the change of supersaturation and the temperature gradient between source and seed for the bulk growth. A series of growth runs on increased source to seed distances was characterized by XRD and Raman spectroscopy. Results show a decrease in quality in terms of single-crystallinity with a decrease in supersaturation. Morphology analysis of as-grown material indicates an increasing protrusion dimension with increasing thickness. This effect limits the achievable maximal thickness. Additional polytype inclusions were observed, which began to occur with low supersaturation (S ≤ 0.06) and prolonged growth (increase of carbon gas-species).

Temperature Investigation on 3C-SiC Homo-Epitaxy on Four-Inch Wafers.

In this work, results related to the temperature influence on the homo-epitaxial growth process of 3C-SiC is presented. The seed for the epitaxial layer was obtained by an innovative technique based on silicon melting: after the first step of the hetero-epitaxial growth process of 3C-SiC on a Si substrate, Si melts, and the remaining freestanding SiC layer was used as a seed layer for the homo-epitaxial growth. Different morphological analyses indicate that the growth temperature and the growth rate play a fundamental role in the stacking faults density. In details, X-ray diffraction and micro-Raman analysis show the strict relationship between growth temperature, crystal quality, and doping incorporation in the homo-epitaxial chemical vapor deposition CVD growth process of a 3C-SiC wafer. Furthermore, photoluminescence spectra show a considerable reduction of point defects during homo-epitaxy at high temperatures.

Growth and Coalescence of 3C-SiC on Si(111) Micro-Pillars by a Phase-Field Approach.

3C-SiC is a promising material for low-voltage power electronic devices but its growth is still challenging. Heteroepitaxy of 3C-SiC on Si micrometer-sized pillars is regarded as a viable method to achieve high crystalline quality, minimizing the effects of lattice and thermal expansion mismatch. Three-dimensional micro-crystals with sharply-faceted profiles are obtained, eventually touching with each other to form a continuous layer, suspended on the underlying pillars. By comparing experimental data and simulation results obtained by a phase-field growth model, here we demonstrate that the evolution of the crystal morphology occurs in a kinetic regime, dominated by the different incorporation times on the crystal facets. These microscopic parameters, effective to characterize the out-of-equilibrium growth process, are estimated by a best-fitting procedure, matching simulation profiles to the experimental one at different deposition stages. Then, simulations are exploited to inspect the role of a different pillar geometry and template effects are recognized. Finally, coalescence of closely spaced crystals ordered into an hexagonal array is investigated. Two possible alignments of the pattern are compared and the most convenient arrangement is evaluated.