We studied and compared the emission properties of optically excited (Al)GaN structures grown by two different techniques: hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD). We successfully achieved stimulated emission (SE) in an HVPE-grown GaN epilayer and a GaN/AlGaN double heterostructure at 10 K and room temperature. We found that the SE threshold and photoluminescence efficiency of the HVPE-grown samples are similar to those of high-quality MOCVD-grown structures. Photoluminescence measurements from 10 to 300 K show that the HVPE GaN has a high density of non-radiative recombination channels, especially those activated below 100 K. This study represents the first demonstration of SE in HVPE-grown (Al)GaN heterostructures.

Four GaN epilayers were grown on sapphire by hydride vapor phase epitaxy. The lattice and thermal expansion coefficient mismatches between the epilayers and the sapphire produce a strain in the structure. The strain at the surface of the epilayers was estimated using photoluminescence. By analyzing the variation of the surface strain with thickness, the minimum thickness required to obtain low surface strain was estimated to be approximately 45 μm. Furthermore, the strain at the interface of the sapphire and the epilayers was estimated after laser lift-off of GaN epilayers. The analysis showed that a low and almost constant strain at the surface of the interface for the separated samples can be obtained for an epilayer thickness greater than 18 μm.

We present a study of the effect of the strain on the anomalous temperature dependence of the photoluminescence (PL) transition energy of three-nanolayer AlxGa1−xN nanoheterostructur∕GaN (0<x⩽0.29) grown on sapphire substrate by hydride vapor phase epitaxy. We proved that this effect is due to the lattice constant and thermal coefficient mismatches among the various layers, especially between the sapphire and GaN epilayers. We separated the nanoheterostructure from its sapphire substrate using a nonbonding laser lift-off technique which we described in details elsewhere. The separation caused the PL peak positions to shift, which proves that a change in the strain took place after the separation and that the mismatches in the physical parameters between the sapphire and the GaN play an essential role in the anomalous behavior. Furthermore, we observed a much better agreement of the transition energy of the temperature dependent PL with the Varshni equation, after the separation.

We have modified the anomalous peak energy of the temperature dependent photoluminescence (PL) of Al x Ga 1-x N/GaN nanoheterostructures (0

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