| Abstract Scope |
Performance of devices grown on partially strain-relaxed InGaN layers is reported. The (In)(Al)GaN material system is highly attractive for many devices, including light emitters from the UV to the visible regions, photovoltaics, power electronics, and thermoelectrics. In particular, In<sub>x</sub>Ga<sub>1-x</sub>N layers with x > 0.2 are necessary for emitters and absorbers in the longer-wavelength visible region, while Al<sub>y</sub>Ga<sub>1-y</sub>N layers with y > 0.4 are desired for deep ultraviolet (UV) emitters. However, strain in such layers can lead to significant defect generation, as well as high piezoelectric fields, which can be detrimental to device performance. Partial strain relaxation via misfit dislocation (MD) formation was recently reported for the first time in semipolar InGaN and AlGaN films, on both (11-22) and (20-21) orientations[1,2], where the basal c-plane acts as the primary slip system. Given the high lattice mismatch of the (Al,In)GaN material system, the availability of a slip system for dislocation glide has significant consequences for semipolar III-nitride devices. However, thus far the critical thickness for relaxation of In<sub>x</sub>Ga<sub>1-x</sub>N layers has not been investigated in the literature beyond x ~ 0.05. In this report, strain relaxed In<sub>x</sub>Ga<sub>1-x</sub>N layers with 0.05 < x < 0.25 have been grown on (11-22) bulk GaN substrates by MOCVD, and characterized by x-ray diffraction, atomic force microscopy, cathodoluminescence, and transmission electron microscopy. We report here for the first time on devices grown on strain-relaxed layers. Long-wavelength light emitting diode (LED) structures were grown on top of partially relaxed InGaN layers, resulting in reduced strain in the active region, which shows promising performance. |