Maryse Lancin

Dynamical Study of Dislocations and 4H → 3C Transformation Induced by Stress in (11-20) 4H-SiC

4H-SiC samples were bent in compression mode at temperature ranging from 400°C to 700°C. The introduced-defects were identified by Weak Beam (WB) and High Resolution Transmission Electron Microscopy (HRTEM) techniques. They consist of double stacking faults bound by 30° Si(g) partial dislocations whose glide locally transforms the material in its cubic phase. The velocity of partial dislocations was measured after chemical etching of the sample surface. The formation and the expansion of the double stacking faults are discussed.

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 973u2009K. 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.

Investigation of Mechanical Stress-Induced Double Stacking Faults in (11-20) Highly N-Doped 4H-SiC Combining Optical Microscopy, TEM, Contrast Simulation and Dislocation Core Reconstruction

Defects are introduced into (11-20) highly N-doped 4H-SiC by one surface scratch followed by annealing at 550°C or 700°C with or without an additional compressive stress. The defects are planar and always consist of double stacking faults dragged by a pair of partial dislocations. In a pair, the partial dislocations have the same line direction, Burgers vector and core composition. All the identified gliding dislocations have a silicon core. An analysis of their expansion during annealing proves that C(g) partial segments can be created but that C(g) partial dislocations are immobile.

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.

Study of Dislocation Mobility in 4H SiC by X-Ray Transmission Topography, Chemical Etching and Transmission Electron Microscopy

Dislocations are introduced by bending in a cantilever mode and annealing under compression. They consist of faulted half loops as shown by chemical etching. Their asymmetric propagation in the sample is attested both by etching and XRTT. Based on such a feature, a nucleation and glide mechanism is proposed. The dislocation velocity and the stress exponent are measured at 550°C. Introduction Structural defects in SiC are being widely studied because of their influence on electrical properties. As for the dislocation dynamics, some information were obtained from plasticity experiments followed by transmission electron microscopy (TEM) observations [1-8]. Such an approach shows that Shockley partial dislocations with silicon core have a higher mobility than those with a carbon core [3,4] but there is still a contradiction with ab-initio calculation for the 90° partial [9]. Moreover, the velocity was not directly measured for perfect or partial dislocations whatever the core. Thus we are carrying direct measurements by chemical etching and X-Ray Transmission Topography (XRTT), the nature of the dislocation core being determined by TEM. This work deals with the first step of that study which consists in exciting specific gliding systems to introduce dislocations at 550, 700 and 1050°C. Their velocity is measured as a function of stress at 550°C. Characterization of the as-grown material We used 4H-SiC wafers provided by CREE, grown along the [11-20] direction by a modified Lely method. Such an orientation is indeed the most convenient to introduce controlled dislocations. XRTT was performed using a Lang set up equipped with an Ag Kα source. The sample is bind to a X-Ray sensitive film and scanned by the beam for a given diffracting family plane defined by its normal g. To characterize the extended defects, different g were chosen. On XRTT images, the dark contrast is due to the strain induced by the extended defects located in the material. Fig. 1 : As-grown [11-20] 4H-SiC: XRTT images (g = 1-101) showing in a ) screw dislocations (1) basal dislocations (2) a micropipe (3) and in b) sub-grain boundaries ; c) HRTEM image viewed along [11-20]. a) c) b) Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 355-358 doi:10.4028/www.scientific.net/MSF.457-460.355

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 1u2009×u20091016u2009cm−2 and with 5u2009×u20091016 He+ cm−2 at 10u2009keV or 50u2009keV 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.