Local strain and potential distribution induced by single dislocations in GaN

Abstract

The presence of a threading edge dislocation terminated at the surface of GaN bulk substrates causes a dipole-like strain state ranging over a several micrometer square area. The local strain state is derived from microphotoluminescence mappings of the near-band-edge spectrum and is quantitatively reproduced by a three-dimensional elastic deformation model approach. These results are compared with the local electrical potential distortion due to the core charge and attracted defects as analyzed by scanning surface-potential microscopy. In contrast to the local strain, the potential profile does not show a dipole-like behavior and decreases laterally faster.

Exciton dynamics at a single dislocation in GaN probed by picosecond time-resolved cathodoluminescence

“…This dipole-like energy shift clearly indicates the presence of an edge or mixed type of dislocation, which induces local strain fields. 18,19 In Fig. 2(d), a continuum elastic model reproduces the dipole-like energy shift with the $1.3 meV difference and $400 nm separation between the two poles, which are consistent with the experimental results.…”

Strain of single edge dislocations in bulk GaN

“…The main direction (maximum to minimum) of the strain dipole is perpendicular to the Burgers vector, i.e. in the 1100 〈 〉 directions [3]. To demonstrate that the measured discrete orientations of the strain dipoles (see Fig.…”

“…(peak-to-peak). This value can be explained quantitatively by taking into account the spatial resolution of our confocal microscope and relaxation at the GaN surface [3]. In regions where the strain fields of several TD overlap, the strain may cancel out or add up.…”

“…These (compared to heteroepitaxial GaN) relatively few TDs are nevertheless still a source of residual strain variations. We were able to measure the strain associated with a single dislocation [3]. For an edge type dislocation the strain variation shows a dipole shaped spatial pattern: the single inserted half lattice-plane of an edge dislocation causes compressive strain on one side and tensile strain on the opposite side of the dislocation line [4].…”

“…nm) intensity and energy shift of the donor bound exciton line (D 0 X), respectively, measured in a micro photoluminescence setup (measurement details are described in Ref. [3]). The D 0 X line is very narrow at low temperatures and the energy difference to the valence band edge is in first approximation constant, so that its position is a good marker for the variation in the band gap energy caused by strain variations.…”