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A nitridated layer of c-plane sapphire was studied by using synchrotron x-ray reflectivity and diffraction measurements. The nitridation of the sapphire surface produced an epitaxial AlN layer with a low mosaicity (1 arcmin) normal to the surface. The nitridation temperature determined the limiting thickness for the nitridated layer. Excessive nitridation beyond the limiting thickness caused strain relaxation by a reduction of lateral domain size and an increase in lateral mosaicity. Therefore, the nitridated layer with compressive strain may provide better nucleation sites for the subsequent GaN overlayer growth than the strain-relaxed one.

Cubic boron nitride (c‐BN) film was deposited on Si(100) substrate using the chemical vapor deposition process assisted by high density plasma of Helicon wave with Borazine (B3N3H6) precursor. It was found that the bombardment of ions with high flux and energy onto the film was necessarily required for synthesizing a c‐BN film. Increasing a negative rf bias on the substrate increased the formation fraction of c‐BN in the film. A nearly pure c‐BN phase was synthesized at the conditions of plasma density in the reactor and rf substrate bias, above 1011 cm−3 and −350 V, respectively. The phase identification of BN film was carried out by the transmission electron microscopy as well as Fourier transformed infrared spectroscopy. The infrared spectra for c‐BN film synthesized at the rf bias of −350 V appeared at 1093 cm−1 with a strong single peak, which is close to a value for the characteristic vibration mode of bulk c‐BN (1065 cm−1). The c‐BN in the film was also confirmed and found to be a fine poly‐crystal...

We investigate the effect of the properties of an intracavity diamond heat spreader on the lasing performance of vertical-external-cavity surface-emitting lasers. We compared two intracavity diamonds with different average birefringences. When a polarization selective element is inserted into the cavity, the infrared output powers are reduced by 13% and 7%, respectively, for the samples with higher and lower average birefringences. The pump-power limited maximum green output powers were changed from 3to5.2W by rotating the samples with lower average birefringence. In order to explain the variation in green output power, the additional round-trip loss caused by diamond birefringence was analyzed theoretically and experimentally. We found that the loss can be reduced when axes of the birefringence are aligned to the axes of the polarization selective element.

We report on the demonstration of highly efficient blue lasers based on intracavity frequency doubling vertical-external-cavity surface-emitting lasers (VECSELs). By optimizing the number of InGaAs quantum wells and employing Al0.3Ga0.7As carrier blocking layers in resonant periodic gain structures, we observed the pump-power-limited output power of 4.5W at 920nm for an InGaAs∕GaAs quantum well VECSEL. With a frequency doubling LiB3O5 crystal inside the cavity, 1.9W continuous-wave 460nm blue output was demonstrated. Power conversion efficiencies (=output power∕pump input power) of 22.5% and 9.5% are realized for λ∼920nm and λ∼460nm, respectively.

The authors report on the development and demonstration of the high power operation of optically end-pumped vertical external cavity surface emitting laser devices emitting at 532 and 460nm. 2.7W green and 1.4W blue output powers were achieved with a good beam quality by intracavity frequency doubling with second harmonic generation crystal. High efficiency and good beam quality are attributed to the enhanced thermal management by the diamond heat spreader directly bonded to the gain region and effective optical pumping by placing the pump laser diode behind the laser structure.

The authors have optimized a resonant gain structure of a 920nm vertical external cavity surface emitting laser. They found that long saturated carrier lifetime in shallow quantum well (QW) under a high injection level restricted the laser performance. An insertion of nonabsorbing layer in the middle of barrier layers with multi-QWs was very effective to reduce the saturated carrier lifetime and, therefore, to enhance the laser performance. With the optimized gain structure, which had ten periods of triple InGaAs QWs with Al0.3Ga0.7As nonabsorbing layers in the middle of GaAs barriers, they achieved 4.9W output power at 10°C.