We present a detailed microphotoluminescence study of the long-range strain fields surrounding threading dislocations as well as their interaction and pattern formation in GaN bulk crystals. The stress patterns are detected by tiny energy shifts of the near-band-edge spectral lines and show a dipolelike stress state around the dislocation core of edge-or mixed-type dislocations, with an angular orientation coinciding with highsymmetry crystal directions. We detect tens of micrometers long linear lineups of edge dislocations with sizable effects on the local strain states and photoluminescence peak positions. With continuum elastic strain simulations, we demonstrate that the observed patterns of threading dislocations are energetically favorable. We calculated a binding energy per threading dislocation length of 50 meV/ m against gliding of an edge dislocation within a lineup of edge dislocations of parallel Burgers vector orientation.

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.

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The current status of InGaN‐MQW‐laser diodes developed at Osram OS is presented. These lasers are grown on n‐conducting SiC, enabling a vertical current path, cleaved facets and excellent heat spreading. The temperature rise during cw operation is measured for different mountings. A p‐side up mounted diode with thermal resistance of 18 K/W showed 143 h of cw lasing at 1 mW optical power (T = 25 °C). DC and pulsed aging shows current as main degradation reason compared to heat for InGaN‐LDs. Photoluminescence spectra of the quantum wells are being compared before and after degradation caused by current.