G. Regula

LACBED study of extended defects in 4H-SiC

Large-angle convergent-beam electron diffraction analysis was successfully performed on pairs of partial dislocations so close that their effect on Bragg lines overlap. These pairs, dragging 3C layers, were nucleated by mechanical deformation of 4H-SiC. Splitting of Bragg lines on crossing a dislocation pair can be interpreted as resulting from a single dislocation having a Burgers vector equal to the sum of the two partial dislocation ones. Splitting rules using phase-shifted reflections ( ) are also given depending on the phase shift produced by 3C lamellae. These results give a direction in agreement with weak-beam dark-field studies and suggest that Si core dislocations have highest mobilities for low-temperature (<700○C) plastic deformation.

Stacking faults in intrinsic and N-doped 4H–SiC: true influence of the N-doping on their multiplicity

The stacking fault multiplicity was studied in intrinsic and N-doped (0001) 4H–SiC. The defects, nucleated by a scratch on the sample surface, expanded during annealing at 973 K. The stacking width was determined by high-resolution transmission electron microscopy. In both materials, the double stacking faults (DSF) are the most numerous defects. Multiple faults, rare, consist of two, three or four successive DSFs. Single stacking faults or odd numbers of stacking faults are never observed. Thus, the α-β phase transformation has little influence on the fault creation and even in N-doped 4H–SiC, the quantum well action only helps the expansion of the DSFs, the already most favourable defects.

Effect of Helium implantation on gettering and electrical properties of 4H‐SiC epilayers

This paper tests the gettering ability of sites created by He implantation in 4H‐SiC while heating the sample or not, and their impact on carrier lifetime. The spatial distribution of implantation‐induced defects (cavities, stacking faults and dislocations) is studied by transmission electron microscopy (TEM) and is compared to gold profiles performed by Rutherford Backscattering (RBS) in samples intentionally contaminated with gold. Minority carrier lifetimes are also measured with a specific set‐up based on microwave photoconductivity decay (μ‐PCD). Though gold atoms do not seem to be efficiently trapped by cavities, the presence of dislocations is of major importance to monitor gold diffusion. Indeed, they can double both its level and its diffusion length in the bulk. Gold is assumed to diffuse faster along dislocation cores. Besides, the implantation‐related defects are found to improve the carrier lifetime in the material, but the role of He2+ left in cavities remains to be investigated.This paper tests the gettering ability of sites created by He implantation in 4H‐SiC while heating the sample or not, and their impact on carrier lifetime. The spatial distribution of implantation‐induced defects (cavities, stacking faults and dislocations) is studied by transmission electron microscopy (TEM) and is compared to gold profiles performed by Rutherford Backscattering (RBS) in samples intentionally contaminated with gold. Minority carrier lifetimes are also measured with a specific set‐up based on microwave photoconductivity decay (μ‐PCD). Though gold atoms do not seem to be efficiently trapped by cavities, the presence of dislocations is of major importance to monitor gold diffusion. Indeed, they can double both its level and its diffusion length in the bulk. Gold is assumed to diffuse faster along dislocation cores. Besides, the implantation‐related defects are found to improve the carrier lifetime in the material, but the role of He2+ left in cavities remains to be investigated.

Study by Weak Beam and HRTEM of double stacking faults created by external mechanical stress in 4H-SiC

4H-SiC samples are bent in compression mode at 550°C and 620°C. The introduced-defects are identified by Weak Beam and HRTEM techniques. They consist of double stacking faults bounded by 30° Si(g) partial dislocations whose glide locally transforms the material in its cubic phase. The velocity of partial dislocations is measured after chemical etching of the sample surface. The formation and the expansion of the double stacking faults are discussed.

Roles of local He concentration and Si sample orientation on cavity growth in amorphous silicon

(111)- and (100)-oriented Si samples were implanted with Si+ ions at 1 MeV to a dose of 1 × 1016 cm−2 and with 5 × 1016 He+ cm−2 at 10 keV or 50 keV and eventually annealed in the 800–1000°C temperature range. Sample characterisation was carried out by cross-section transmission electron microscopy, positron annihilation spectroscopy and nuclear reaction analysis. In addition to the formation of He bubbles at the projected range of He, bubbles were observed after solid-phase epitaxial growth (SPEG) of the embedded amorphous Si layer. The He threshold concentration required to obtain thermally stable bubbles in amorphised Si is between one and four orders of magnitude lower than in c-Si. Since bubble formation and growth take place in the a-Si phase, the interaction with SPEG during annealing was studied by considering (100) and (111) Si. Both the SPEG velocity and the resulting defects play a role on bubble spatial distribution and size, resulting in bigger bubbles in (111) Si with respect to (100) Si.

Defect generation and characterization in 4H-SiC

Study of extended defects in 4H-SiC actually receives particular attention since high quality samples are now available while mechanisms of defect nucleation and propagation are still subject of debate. Indeed, several works revealed that Schockley partial dislocations easily propagate in the brittle regime, leading to the extension of simple [1] and multiple stacking faults [2,3] depending on the deformation conditions. Some of them also bring forth the influence of the n doping on the stacking fault multiplicity [4]. In addition, recent experiments suggest that Si(g) core segments are more mobile than C(g) dislocations [1,5] whereas opposite behaviour is expected from atomistic simulations [6]. Intensive works are thus now focused on the determination of the respective influences of doping and mechanical stress on the defect nature in 4HSiC.

Core Composition of Partial Dislocations in N-Doped 4H-SiC Determined by TEM Techniques, Dislocation Core Reconstruction and Image Contrast Analysis

Defects were created in N-doped 4H-SiC by cantilever bending from a scratch on the (1120) surface under compression. They consist of two stacking faults (double stacking faults) expanding from the scratch in [1100] or [1100] directions. The character and core composition of the leading Shockley partial dislocations were determined by coupling WB, LACBED, contrast analysis of (1120) HRTEM images and dislocation core reconstructions. Each double stacking fault is due to the glide of a pair of identical Si-core partial dislocations in two adjacent glide planes in which the Si-C dumbbells exhibit the same orientation. Such a feature as well as the asymmetrical expansion of the defects is related to lack of mobility of C-core partial dislocations in that range of temperatures (550 °C-700 °C).

Links Between Etching Grooves Of Partial Dislocations And Their Characteristics Determined By TEM In 4H SiC

We introduce defects into ) 0 2 11 ( oriented highly N-doped 4H-SiC by surface scratching, bending and annealing in the brittle regime. Emerging defects at the sample surface are revealed by chemical etching of the deformed samples. The etch patterns are constituted of straight bulges exhibiting various topographical features. These etch figures correspond to the emergence of double stacking faults dragged by a pair of partial dislocations. In this paper, we discuss the links between the etch figure characteristics and the defect nature. Results obtained by optical and atomic force microscopy are completed by structural analysis of defects performed by transmission electron microscopy. Mobility of partial dislocations in 4H-SiC is discussed and correlated to their core composition and to the effect of the applied mechanical stress.

Evolution of nucleation sites and bubble precursors in silicon as a function of helium implanted dose

(111) oriented silicon samples were implanted at room temperature with 1.55 MeV 3 He ions in the dose range of 5×10 15 to 5×10 16 /cm 2 . Cross-sectional transmission electron microscopy (XTEM) was used to study the evolution of bubbles and extended defects during subsequent thermal annealing at 800°C and 900°C for 30min. The He desorption from bubbles and bubble precursors was measured by means of nuclear reaction analysis (NRA). TEM observations show that no bubbles were observed in Si implanted at doses lower than 1×10 16 /cm 2 , while a well-defined cavity band was formed after implantation at 5×10 16 /cm 2 and subsequent thermal annealing. At the intermediary dose of 2×10 16 /cm 2 , however, the evolution of bubbles and extended defects is quite different. The bubbles prefer to nucleate in large planar clusters surrounded by a high density of dislocation loops emerging from them. The clusters of bubbles act as the sources of the dislocation loops. NRA measurements indicate that the He desorption behavior is also dose-dependent. The He desorption is achieved much faster in low dose implanted Si. The results are qualitatively discussed.