In this work we present the optical micro-analysis of violet light emitting laser structures grown on bulk GaN substrates. These lasers, because of high structural quality and low defect concentration have a great potential as a high power sources of violet and UV light. It is however, an open question whether the reduced density of dislocation influences homogeneity of InGaN quantum wells and what degradation mechanisms are important for aging processes in these devices.
We carried out our investigation using new and degraded (subdue to aging precedure) laser diodes grown by MOVPE method on high-pressure synthesized bulk GaN crystals. We compare the results with these obtained by MBE on identical substrates. The active region of our lasers consists on an InGaN/InGaN multiple quantum well (MQW) emitting blue light around 405nm, placed between GaN or InGaN guiding layers and GaN/AlGaN superlattices as n- and p-cladding. Laser stripes are 600µm long of width between 5µm and 20µm. The microscopic properties of these completely processed laser structures and MQW are analysed by spectrally resolved cathodoluminescence microscopy (CL). The individual layer sequence of the laser was revealed by cross-sectional CL, showing, e.g., the luminescence of the cladding layers, the MQW, and the p-GaN. The lateral homogeneity of the whole laser was measured by highly spatially resolved plan-view CL imaging. We studied structures containing InGaN quantum wells of various widths (from 3 up to 17 nm). We demonstrate an outstanding homogeneity of the light emission from the above mentioned structures which may imply the reduced In composition fluctuations in the high crystalline structures. Finally, we will also comment on the determination of post-aging defects present in our laser structures.

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