Search

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 3 to 5.2 W 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. [ABSTRACT FROM AUTHOR]

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 4.5 W at 920 nm for an InGaAs/GaAs quantum well VECSEL. With a frequency doubling LiB3O5 crystal inside the cavity, 1.9 W continuous-wave 460 nm blue output was demonstrated. Power conversion efficiencies (=output power/pump input power) of 22.5% and 9.5% are realized for λ∼920 nm and λ∼460 nm, respectively. [ABSTRACT FROM AUTHOR]

It is known that due to the formation of in-plane local energy barrier, V-defects can screen the carriers which non-radiatively recombine in threading dislocations (TDs) and hence, enhance the internal quantum efficiency in GaN based light-emitting diodes. By a theoretical modeling capable of describing the inhomogeneous carrier distribution near the V-defect in GaN based quantum wells, we show that the efficient suppression of non-radiative (NR) recombination via TD requires the local energy barrier height of V-defect larger than ∼80 meV. The NR process in TD combined with V-defect influences the quantum efficiency mainly in the low injection current density regime suitably described by the linear dependence of carrier density. We provide a simple phenomenological expression for the NR recombination rate based on the model result. [ABSTRACT FROM AUTHOR]

We report the characteristics of forward tunneling current in InGaN/GaN multiple quantum well light-emitting diodes (LEDs) grown on Si (111) substrate. Temperature-variable current-voltage (I-V) measurement from 80 K to 400 K reveals that forward current regimes can be distinguished by corresponding slopes in semi-logarithmic plot, which are associated with different forward conduction mechanisms of InGaN LED. Temperature-insensitive tunneling behavior appears to be dominant at low current injection regime for InGaN LEDs on Si. Conductive atomic force microscopy analysis indicates that V-pits associated with threading dislocations could be main leakage path of forward tunneling current of InGaN LED on Si. [ABSTRACT FROM AUTHOR]

The effect of surface treatment on leakage current is investigated for two structures of the electropumped GaAs/AlGaAs laser microcavities, one with mesa and the other with hyperboloid-drum structures. Using surface sheet resistivity as a figure-of-merit parameter, the results of different surface treatment methods are compared. The best result is obtained when the sample has been polished in a H[SUB2]SO[SUB4]:H[SUB2]O[SUB2]:H[SUB2]O = 1:8:1000 solution for 5 s, and treated subsequently in a 6% excess sulfur-containing (NH[SUB4])[SUB2]S[SUBx] (solution at 60 °C for 8 mins. The treatment in (NH[SUB4])[SUB2]S[SUBx] solution increases the surface sheet resistivity by a factor of ∼ 14. The cross-sectional shape of the cavity and the vertical profile of distributed Bragg reflector mirrors have little correlation with the leakage current. [ABSTRACT FROM AUTHOR]