Among the limitations known from semiconductor lasers, catastrophic optical damage (COD) is perhaps the most spectacular power‐limiting mechanism. Here, absorption and temperature build up in a positive feedback loop that eventually leads to material destruction. Thus, this is truly an ultimate mechanism, and its continued suppression is a manifestation of progress in device design and manufacturing. After an overview of the current state of knowledge, new investigations of COD using artificially micrometer‐sized starting points created within the active zone in the cavity of 450 nm GaN semiconductor lasers are reported on. Defect growth mechanisms and characteristics are studied during 800 ns current pulses. The defect growth follows the highest light intensity. Secondary defect patterns are studied: complete destruction of the active zone and generation of a point defect cloud at least ≈10 μm into the remaining surrounding material. Extremely large angles (>90°) of damage growth are traced back to the material properties and the aging scenario. The results are compared with former experiments with GaAs‐based lasers.

We present an analysis of optical and thermal properties of GaN-based blue-emitting high-power diode laser arrays (bars). Parameters such as emission power and temperature are monitored for each single emitter of arrays consisting of 23 emitters. The obtained data are compared with modeling of the electro-optic properties. In contrast to the well-known infrared bars, the thermal properties in the blue-emitting bars control the individual emitter properties to a very high degree and lead to considerable variations in emitter power, in extreme cases up to 50%. Such extreme cases occur, for example, when emitters fail and thus act as a heat source for their surroundings. Nevertheless these bars reach record output powers and are on the way to becoming major sources of photonic power in the blue spectral range.

Yellow emissions at 580 nm from the operation of 450 nm emitting (In,Ga,Al)N diode lasers are investigated. Spatial and spectral behaviors were analyzed and modeled. Consistent results were obtained and the emission was identified coming from the active region of the laser. This emission has the potential to be useful for analytical purposes, e.g. for the determination of refractive indices or the visualization of non-equilibrium carrier profiles along devices. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Except for their primary emission, diode lasers frequently show emissions at lower photon energies. We present a study in which we record and analyze emission images of (In,Ga,Al) N-based 450 nm emitting diode lasers. Imaging is realized in the spectral ranges of two broad secondary emission bands, which are peaking in the yellow region at 580 nm (VIS) and in the infrared at 875 nm (IR). Both bands have their principal origin in the active region of the device. The VIS emission spectrum looks like the well-known yellow GaN-emission, but comes exclusively from the active region. It is very likely an electroluminescence that involves trapping of non-equilibrium carriers into defects located in the active region, followed by radiative recombination under emission of VIS photons. The IR emission involves also emission from the active region, but significant contributions are also observed in the substrate. The latter contribution could be generated by absorption of spontaneous primary emissions there. Moreover, we modelled emission images by raytracing. This allows the determination of absorption coefficients and refractive indexes of the active region, the unpumped epitaxial layer, and the substrate. The VIS signal from the active region proved to be proportional to the non-equilibrium carrier concentration. This makes it potentially interesting for analytical purposes, e.g., the imaging of carrier concentration profiles.

The catastrophic optical damage (COD) of 450-nm emitting InGaN/GaN diode lasers is investigated with special attention to the kinetics of the process. For this purpose, the COD is triggered artificially by applying individual current pulses. This makes it possible to achieve a sub-µs time resolution for processes monitored by cameras. COD appears as a "hot" process that involves decomposition of quantum well and waveguide materials. We observe the ejection of hot material from the front facets of the laser. This can be seen in two different wavelength ranges, visible/near infrared and mid infrared. The main contributions identified are both thermal radiation and 450-nm laser light scattered by the emitted material. Defect growth during COD is energized by the optical mode. Therefore, the defect pattern resembles its shape. Ultimately, the loss of material leads to the formation of an empty channel along the laser axis. COD in GaAs and GaN-based devices follows similar general scenarios. After ignition of the process, the defect propagation during the process is fed by laser energy. We observe defect propagation velocities of up to ~30 m/s for GaAs-based devices and 110 m/s for GaN-based devices. The damage patterns of GaN and GaAs-based devices are completely different. For GaN-based devices, the front facets show holes. Behind them in the interior, we find an empty channel at the position of the optical mode surrounded by intact material. In contrast, earlier studies on GaAs-based devices that were degraded under almost identical conditions resulted in molten, phase separated and both recrystallized and amorphous materials with well-defined melting fronts.

Gallium-nitride-based diode lasers were intentionally damaged using single sub-μs current pulses. This approach provoked catastrophic optical damage, a known sudden degradation mechanism, which becomes evident as surface modification at the aperture, where the 450-nm laser emission leaves the waveguide of the device. Subsequently, we analyzed the related damage pattern inside the device. Knowledge about the operating conditions, degradation time, and energy introduced into the defect allows estimates of the temperature during the process (∼ 1000°C) and defect propagation velocity (110 μm/μs). Further analysis of this data allows for conclusions regarding the mechanisms that govern defect creation at the surface and defect propagation inside the device. Moreover, we compared these findings with earlier results obtained from gallium-arsenide-based devices and find similarities in the overall scenario, while the defect initialization and defect pattern are strikingly different.

Damage patterns caused by Catastrophic Optical Damage (COD) are analyzed in GaN-based high-power diode lasers. We find the process to result in material loss including the formation of an empty channel. This is consistent with the observation of ejections of hot material out of the front facet of the device during COD. In the immediate vicinity of the empty channel, the laser structure seems to be absolutely undisturbed. These results are compared with earlier results from comparable experiments obtained with GaAs-based devices. While the COD process in both material systems follows similar scenarios and root causes, the damage pattern differs substantially. The completely empty channel at the position of the optical mode is in striking contrast to the results of earlier studies in GaAs-based devices, degraded under almost identical conditions. There molten, phase segregated, and both recrystallized and amorphous materials with well-pronounced melting fronts are observed. In the GaN-based devices we observe average defect front propagation velocities along the laser axis of 110 m/s. This is faster by a factor of 4–5 than what has been observed in GaAs-based devices under comparable experimental conditions.

Shortwave infrared emission from 450 nm InGaN diode lasers is analyzed, and its physical origin is located by SWIR imaging of operating devices. Emission spectra taken in the 900-1700 nm range reveal three main contributions located at 900-1130 nm, 1130-1350 nm, and beyond 1350 nm. In concert with photoluminescence measurements at the substrate, these emission bands are identified as, first, genuine deep-level electroluminescence from the active region and deep-level defect-related emission from the substrate that is pumped by spontaneous 450 nm primary emission, second, pure deep-level defect emission, and third, Planck’s black-body radiation from the entire heated device and an additional deep-level defect contribution.