Search

We have demonstrated a high-power 980-nm vertical-cavity surface-emitting laser diode (VCSEL) array with ion-implanted current apertures. The device was characterized on an exclusively developed water-cooled heat sink for the VCSEL array. A peak output power of over 200 W has been achieved under quasi-continuous-wave operation at a cooling water temperature of 10 °C. The VCSEL array consists of 635 emitters, which were defined by proton implantation and arranged in a closest packed arrangement with 175- \(\mu \) m-spacing in \(5~{\rm mm} \times 5\) mm square. The results provide a chance to the next step for a higher-power VCSEL array.

We report on the long-term reliable continuous wave (CW) operation of high-power and high-efficiency 915-nm broad-area laser diodes (BA-LDs). An output power of over 20 W and a maximum power-conversion efficiency of over 65% have been marked at a heat-sink temperature of 20 °C. Stable operations of over 5000 h have also been achieved for the 915-nm and 976-nm BA-LDs with CW output powers of 20 W, respectively. The window structure with a bandgap difference of 100 meV provides the reliable operation at the high-output power range.

We report on laser lift-off (LLO) of AlN/sapphire for UV light-emitting diodes (LEDs). Underfill between chip and submount is a key factor for the successful LLO of AlN/sapphire. We fabricated thin-film-flip-chip UV LEDs with a peak wavelength of 343 nm using the LLO. Moreover surface texturing was carried out on the exfoliated AlN surface. The light output power from the UV LED after the LLO and the surface texture at exfoliated surface is 1.7 times higher than that before the LLO at 20 mA (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The crystalline quality of GaN and Al0.08Ga0.92N epitaxial layers on (100) β-Ga2O3 substrates was significantly improved by the facet-controlled growth method. The facets were controlled by changing the nitrogen ambient thermal annealing temperature. We demonstrated the high-crystalline-quality GaN and Al0.08Ga0.92N on β-Ga2O3 substrates, which were comparable to GaN and AlGaN on sapphire substrates using low-temperature buffer layers. This method is useful for the fabrication of vertical-type ultraviolet (UV) light-emitting diodes (LEDs) on β-Ga2O3 substrates. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We evaluated AlGaN-based 355 nm UV laser diodes prepared under two different Mg activation conditions. The annealing processes for Mg activation in p-layers were carried out under N2 or O2 ambient to investigate the effect of the ambient gas on the laser characteristics. The threshold current densities and operating voltages of the UV laser diodes were improved by annealing under O2 compared with those under N2. We then estimated the injection efficiencies of the laser diode structures by considering the internal quantum efficiencies of optical excitation and electrical excitation. The internal quantum efficiency of the electrically excited spontaneous emission from the laser structure annealed under O2 reached 50% at a carrier density of 7.0×1018 cm-3, while the structure annealed under N2 required a 1.8-fold higher carrier density of 1.2×1019 cm-3 to reach the same internal quantum efficiency. In addition, the internal quantum efficiency estimated from optical excitation reached 50% even at a carrier density of 3.0×1018 cm-3. This implies that the injection efficiencies in the UV laser diode structures annealed under N2 and O2 were 25% and 45%, respectively. Mg activation by O2 annealing is effective for increasing the injection efficiency. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

For large-area ion-implanted vertical-cavity surface-emitting lasers (VCSELs), side emission from the edges of a chip disturbs the laser emission of a VCSEL mode, and suppression of it is fundamental. In this paper, we present results of a numerical investigation of the side emission from large-area VCSELs. We have modeled a VCSEL structure by an infinitely broad layer structure with mirror loss at the edge surfaces. Estimated threshold gains indicate that laser emission occurs either in a VCSEL mode or in an edge-emitting Fabry-Perot (EEFP) mode. Calculated emitter length dependence of the threshold gain of these modes shows good agreement with experimental results, and the side emission is verified to be the laser emission of the EEFP mode. We have also discussed the way to suppress the side emission and confirmed that our recent achievement of over 200 W quasi-continuous-wave output from an ion-implanted VCSEL array is due to antireflection coatings of the edges and introduction of optical losses in ex-emitter regions.

We investigated indium–tin oxide (ITO)/Al reflective electrodes for improving the light extraction efficiency of UV light-emitting diodes (LEDs). The ITO layer showed high transparency in the UV region upon optimization of the thickness and annealing temperature. As a result, the ITO/Al electrode exhibited both high reflectivity in the UV region and good contact characteristics simultaneously. Using this electrode, we succeeded in improving the light output power of a 350 nm UV-A LED.