Indentation of GaN: A Study of the Optical Activity and Strain State of Extended Defects

Abstract

Extended defects such as dislocations were induced by nano‐ and microindentation in GaN layers grown by molecular beam epitaxy on 6H‐SiC. The resulting local variation of the strain and optical properties were investigated by spectrally and spatially resolved cathodoluminescence. The microindentation causes an evolution of dark‐line defects, compressive strain within the region of the defects, and cracking along directions determined by the symmetry of the arrangement of the dark‐line defects. The evolution of extended dark‐line defects is correlated with the dislocation structure, which was analyzed by transmission electron microscopy measurements of the plastically deformed indented regions.

Strain Rate Controlled Nanoindentation Examination and Incipient Plasticity in Bulk GaN Crystal

“…4 indicate basal c-plane slips, which are recognized as the easiest slip system in GaN crystal. [6][7][8][9][10][11][12][13] However, the c-plane basal slip system cannot move at the first moment of plastic deformation for m-axis directed indentation (see Table I). Additionally, if the c-plane slip system is stimulated prior to the other slip systems, the vertical slip lines should be grouped around the highest shear stress line, which is at the center vertical line beneath the indented surface.…”

“…Past studies have investigated the dislocation formation and movement in indented surface dimples on c-plane GaN by using cross-section transmission electron microscopy (TEM). [6][7][8][9][10][11][12] One report has suggested that the basal c-plane in GaN crystal is the main slip system and the pyramidal Splane (10 11) is the secondary one for progressing plasticity accompanied by dislocation multiplication for c-axis directed macroscopic indentation, which exceed 10 mN and 100 nm. 6) Taking into account the Schmid factor (Table I), we notice that the initial plastic deformation cannot be attributed to the c-plane slip system (see also Ref.…”

Mechanical Deformation Behavior of Nonpolar GaN Thick Films by Berkovich Nanoindentation

“…3 c and f, which act as a result of dislocations glide in the {0001} plane. At the slip-plane crossing, these defect-related stresses are expected to increase drastically due to dislocation pile-ups [ 18 ], and consequently, cracks could be preferably nucleated along the direction. It is thus evidenced that slip is the major mode of plastic deformation in nonpolar m -plane GaN.…”

Dislocation luminescence in GaN single crystals under nanoindentation

“…Especially, there has also been a considerable effort to determine the properties of plastic deformation in GaN epilayers and GaN bulk crystals using indentation techniques [ 6 - 14 ]. Local strain fields of the indentation have been studied by a micro-Raman spectroscopy [ 11 , 13 ], and the formation of contact-induced dislocations has been investigated via cathodoluminescence (CL) spectroscopy [ 6 - 9 , 11 ] and transmission electron microscopy (TEM) [ 6 - 8 , 10 , 12 ]. However, most of these earlier studies mainly focused on the microstructure of the indentation-induced dislocations in GaN; the fundamental dislocation luminescence mechanism of GaN is not understood fully.…”