We develop a reciprocal-space model that describes the (hkl) dependence of the broadened Bragg peakwidths produced by x-ray diffraction from a dislocated epilayer. We compare the model to experiments and find that it accurately describes the peakwidths of 16 different Bragg reflections in the [010] zone of both GaN and AlN heterolayers. Using lattice-distortion parameters determined by fitting the model to selected reflections, we estimate threading-dislocation densities for seven different GaN and AlGaN samples and find improved agreement with transmission electron microscopy measurements.

In-situ stress monitoring has been employed during metalorganic chemical vapor deposition of AIGaN/GaN distributed Bragg reflectors (DBRs). It was found that the insertion of multiple AIN interlayers is effective in converting the tensile growth stress typically observed in this system into compression, thus alleviating the problem of crack generation. Crack-free growth of a 60-pair Alo.z5G~.75N/GaN quarter-wavelength DBR was obtained over the entire two-inch wafer; an accompanying reflectivity of at least 9970 was observed near the peak wavelength around 380 nm.-Email address: jhml@sandia.gov I

Using in situ wafer-curvature measurements of thin-film stress, we determine the critical thickness for strain relaxation in AlxGa1−xN∕GaN heterostructures with 0.14⩽x⩽1. The surface morphology of selected films is examined by atomic force microscopy. Comparison of these measurements with critical-thickness models for brittle fracture and dislocation glide suggests that the onset of strain relaxation occurs by surface fracture for all compositions. Misfit-dislocations follow initial fracture, with slip-system selection occurring under the influence of composition-dependent changes in surface morphology.

We demonstrate that the insertion of low-temperature (LT) AIGaN interlayers is effective in reducing mismatch-induced tensile stress and suppressing the formation of cracks during growth of AIGaN dkectly upon GaN epilayers., Stress evolution and relaxation is monitored using an in-situ optical stress sensor.

We have designed and implemented a vertical cavity violet light emitting diode which features an optical resonator composed of an in situ grown GaN/AlGaN DBR and a high reflectivity dielectric mirror. The active InGaN MQW medium is grown directly atop the AlGaN DBR and the structure includes an intracavity lateral current spreading layer based on a p++/n++ InGaN/GaN tunnel junction. Electroluminescence shows directional emission, with modal linewidths as narrow as 0.6 nm.