The study of SiC has been recently developed significantly because the physical and electrical properties of its basic polytypes, making it suitable as promising semiconductor material for electronic devices. Nevertheless, the device performance is often compromised by the grown-in structural defects such as dislocations, micropipes, grain boundaries, misoriented areas, etc. [1]. Moreover, due to the low staking fault energy, it is difficult to obtain single polytype material during bulk crystal growth and, consequently, it is common to find the coalescence of 6H, 4H, 15R and 3C polytypes. These polytypes differ among them for different ordered stacking sequences of SiC bilayers. Different stacking of bilayers can also generate twins but, unfortunately, works that investigate the twins of SiC are quite rare. Although several improvements have been recently obtained on the reduction of the micropipes and of the density of dislocations [2], the presence of several structural defects in the SiC crystals remains a problem that has not yet been solved. In this contribution it has been reports the results a twin micro-lamella of 15R, embedded in a macro-lamella of 15R enclosed in 6H-SiC wafer. The wafer, grown by PVT method, shows a complex syntactic coalescence of polytypes that was previously investigated by means of X-Ray Diffraction Topography, using both White-Beam-Synchrotron-Radiation-Source and MoKα1 conventional source and μ-Raman Spectroscopy. This earlier multi-analytical study permitted to localize and to identify the twin lamella that, subsequently, was prepared for TEM analyses. The electron diffraction patterns (SAPDs) taken exactly above the interface of the micro-lamella show the presence of twinning. In order to determine the twin law, comparisons among SAPDs and simulations of the diffraction pattern introducing all the possible twin operations were carried out. Moreover, taking into account also the XRDT and μ-Raman data previously obtained, it has been found that the twin law consists of π-rotation around [0001] with (0001) as composition plane. Additionally, the analysis of SAPDs permits also to determine that the twin index is 3 and the obliquity is zero. High Resolution (HRTEM) images of the twin boundaries reveal that the interpretation of the contrasts is not trivial because of the presence of numerous adjoining stacking faults parallel to (0001)with interleaving (33) and (22) lamellae. The Fourier Transform calculated across the boundary (33)/(22) does not shows any splitting and thus this sequence introduce no twinning within the 15R but consists of 4H and 6H like sequences. On the contrary, HRTEM images taken across the boundaries can be interpreted with reference to the primitive oblique 2D cell of the 15R polytype as a zig-zag pattern (23) that switches to (32) by a twin coherent interface or, alternatively, as zig-zag pattern (32) which pass to (23) trough an isolated (33) lamella. In other words, the twin interface can be also considered as the interposition of a 6H lamella and thus the origin of the twin lamella is strictly related to the stacking faults. Consequently, it can be concluded that the low energy of stacking faults in 15R SiC [3] favours also the growth of twin lamellae.

Agrosì, G., Capitani, G., Scandale, E., Tempesta, G. (2008). TWIN LAMELLA CHARACTERIZATION OF 15R SiC BY MEANS OF TRANSMISSION ELECTRON MICROSCOPY. Intervento presentato a: 1st SIMP-AIC joint meeting, Sestri Levante (Italy).

TWIN LAMELLA CHARACTERIZATION OF 15R SiC BY MEANS OF TRANSMISSION ELECTRON MICROSCOPY

CAPITANI, GIANCARLO;
2008

Abstract

The study of SiC has been recently developed significantly because the physical and electrical properties of its basic polytypes, making it suitable as promising semiconductor material for electronic devices. Nevertheless, the device performance is often compromised by the grown-in structural defects such as dislocations, micropipes, grain boundaries, misoriented areas, etc. [1]. Moreover, due to the low staking fault energy, it is difficult to obtain single polytype material during bulk crystal growth and, consequently, it is common to find the coalescence of 6H, 4H, 15R and 3C polytypes. These polytypes differ among them for different ordered stacking sequences of SiC bilayers. Different stacking of bilayers can also generate twins but, unfortunately, works that investigate the twins of SiC are quite rare. Although several improvements have been recently obtained on the reduction of the micropipes and of the density of dislocations [2], the presence of several structural defects in the SiC crystals remains a problem that has not yet been solved. In this contribution it has been reports the results a twin micro-lamella of 15R, embedded in a macro-lamella of 15R enclosed in 6H-SiC wafer. The wafer, grown by PVT method, shows a complex syntactic coalescence of polytypes that was previously investigated by means of X-Ray Diffraction Topography, using both White-Beam-Synchrotron-Radiation-Source and MoKα1 conventional source and μ-Raman Spectroscopy. This earlier multi-analytical study permitted to localize and to identify the twin lamella that, subsequently, was prepared for TEM analyses. The electron diffraction patterns (SAPDs) taken exactly above the interface of the micro-lamella show the presence of twinning. In order to determine the twin law, comparisons among SAPDs and simulations of the diffraction pattern introducing all the possible twin operations were carried out. Moreover, taking into account also the XRDT and μ-Raman data previously obtained, it has been found that the twin law consists of π-rotation around [0001] with (0001) as composition plane. Additionally, the analysis of SAPDs permits also to determine that the twin index is 3 and the obliquity is zero. High Resolution (HRTEM) images of the twin boundaries reveal that the interpretation of the contrasts is not trivial because of the presence of numerous adjoining stacking faults parallel to (0001)with interleaving (33) and (22) lamellae. The Fourier Transform calculated across the boundary (33)/(22) does not shows any splitting and thus this sequence introduce no twinning within the 15R but consists of 4H and 6H like sequences. On the contrary, HRTEM images taken across the boundaries can be interpreted with reference to the primitive oblique 2D cell of the 15R polytype as a zig-zag pattern (23) that switches to (32) by a twin coherent interface or, alternatively, as zig-zag pattern (32) which pass to (23) trough an isolated (33) lamella. In other words, the twin interface can be also considered as the interposition of a 6H lamella and thus the origin of the twin lamella is strictly related to the stacking faults. Consequently, it can be concluded that the low energy of stacking faults in 15R SiC [3] favours also the growth of twin lamellae.
abstract + poster
SiC, stacking faults, polytypism, HRTEM
English
1st SIMP-AIC joint meeting
2008
2008
34
193
none
Agrosì, G., Capitani, G., Scandale, E., Tempesta, G. (2008). TWIN LAMELLA CHARACTERIZATION OF 15R SiC BY MEANS OF TRANSMISSION ELECTRON MICROSCOPY. Intervento presentato a: 1st SIMP-AIC joint meeting, Sestri Levante (Italy).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/31416
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