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.

Time resolved scanning near-field optical microscopy was employed to study spatial and temporal dynamics of III-nitride-system-based blue light emitting laser diodes with a ridge width of 20 μm deposited on high pressure grown bulk GaN substrate. Devices were driven in a pulse regime with a current pulse length of 500 ns. Temperature effects and fluctuation in carrier concentration resulted in a complicated dynamic picture of the photon field evolution. The guided modes did not reach a stable form during a driving pulse. Due to a large antiguiding factor which is characteristic for nitride compounds, filamentation processes were clearly observable leading to the formation of up to four filaments across the ridge, each about 3 μm. Analysis of spatial and temporal evolution of the guided mode revealed strong light leakage into the highly absorptive substrate. Separation between the adjacent cavity modes equals to 0.57 nm which corresponds to the cavity length of 50 μm being very close to the thickness of GaN substrate. Detection of near-field-to-far-field evolution evidenced a considerable beam steering as a result of temperature and carrier induced refractive index changes.

No abstract

We used single crystals of GaN, obtained from high-pressure synthesis, as substrates for Metalorganics Vapor Phase Epitaxy growth of violet and UV laser diodes. The use of high-quality bulk GaN leads to the decrease of the dislocation density to the low level of 105 cm−2, i.e. two orders of magnitude better than typical for the Epitaxial Lateral Overgrowth laser structures fabricated on sapphire. The low density and homogeneous distribution of defects in our structures enables the realization of broad stripe laser diodes. We demonstrate that our laser diodes, having 15 μm wide stripes, are able to emit 1.3-1.9 W per facet (50% reflectivity) in 30 ns long pulses. This result, which is among the best ever reported for nitride lasers, opens the path for the development of a new generation of high power laser diodes.

In this work we present a reliability study of low dislocation density InGaN laser diodes fabricated on high‐pressure grown GaN monocrystaline substrates. The aging process was performed under pulse current conditions. Degradation of these devices manifests primarily in the increase of the threshold current. Interestingly, the differential efficiency of lasers remains stable at all times. The aging time dependence of the increase of the threshold current precisely follows a square root dependence. These observations suggest that the degradation results from the enhancement of the nonradiative recombination within the device active layers and is related to point defect diffusion. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)