We have investigated the aging processes in InGaN laser diodes fabricated by metal organic vapor phase epitaxy on low-dislocation-density, high-pressure-grown bulk gallium nitride crystals. The measured threshold current turned out to be a square root function of aging time, indicating the importance of diffusion for device degradation. The differential efficiency, in contrast, was roughly constant during these experiments. From these two observations we can conclude that the main reason for degradation is the diffusion-enhanced increase of nonradiative recombination within the active layer of the laser diode. Additionally, microscopic studies of the degraded structures did not reveal any new dislocations within the active area of the aged diodes, thus identifying point defects as a source of nonradiative processes.

In this paper we present an extensive theoretical and numerical analysis of monolithic high-index contrast grating, facilitating simple manufacture of compact mirrors for very broad spectrum of vertical-cavity surface-emitting lasers (VCSELs) emitting from ultraviolet to mid-infrared. We provide the theoretical background explaining the phenomenon of high reflectance in monolithic subwavelength gratings. In addition, by using a three-dimensional, fully vectorial optical model, verified by comparison with the experiment, we investigate the optimal parameters of high-index contrast grating enabling more than 99.99% reflectance in the diversity of photonic materials and in the broad range of wavelengths.

In this work, we study the thermal degradation of In-rich In x Ga1–x N quantum wells (QWs) and propose explanation of its origin based on the diffusion of metal vacancies. The structural transformation of the In x Ga1–x N QWs is initiated by the formation of small initial voids created due to agglomeration of metal vacancies diffusing from the layers beneath the QW. The presence of voids in the QW relaxes the mismatch stress in the vicinity of the void and drives In atoms to diffuse to the relaxed void surroundings. The void walls enriched in In atoms are prone for thermal decomposition, what leads to a subsequent disintegration of the surrounding lattice. The phases observed in the degraded areas of QWs contain voids partly filled with crystalline In and amorphous material, surrounded by the rim of high In-content In x Ga1–x N or pure InN; the remaining QW between the voids contains residual amount of In. In the case of the In x Ga1–x N QWs deposited on the GaN layer doped to n-type or on unintentionally doped GaN, we observe a preferential degradation of the first grown QW, while doping of the underlying GaN layer with Mg prevents the degradation of the closest In x Ga1–x N QW. The reduction in the metal vacancy concentration in the In x Ga1–x N QWs and their surroundings is crucial for making them more resistant to thermal degradation.

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By using an atypically wide quantum well (95Å) in the active layer of InGaN violet light emitting laser diode, we managed to fabricate a device characterized by very high thermal stability of the threshold current. The characteristic T0 temperature was measured to be 302K, which is the highest reported value up to date. After thermal cycling of the device, T0 drops down to the lower value of 220K. The very high value of T0 in our devices is accompanied by anomalous temperature behavior of the device slope efficiency. The slope efficiency improves with increasing temperature, reaches a maximum and then gradually decreases. This behavior we interpret as the competition between a regular increase of the thermal carrier escape and an improvement of carrier capture efficiency with an opposite temperature dependence. The latter mechanism we tentatively attribute to the temperature quenching of the ballistic transport related carrier leakage from the active region of the laser diode.