Here, we report the cw laser operation of electrically pumped GaN-based vertical cavity surface emitting laser (VCSEL). The GaN-based VCSEL has a ten-pair $\mathrm{In}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ multiple quantum well active layer embedded in a GaN hybrid microcavity of $5\lambda$ optical thickness with two high reflectivity mirrors provided by an epitaxially grown $\mathrm{Al}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ distributed Bragg reflector (DBR) and a ${\mathrm{Ta}}_2{\mathrm{O}}_5∕\mathrm{Si}{\mathrm{O}}_2$ dielectric DBR. cw laser action was achieved at a threshold injection current of $1.4\mathrm{mA}$ at $77\mathrm{K}$ . The laser emitted a blue wavelength at $462\mathrm{nm}$ with a narrow linewidth of about $0.15\mathrm{nm}$ . The laser beam has a divergence angle of about 11.7° with a polarization ratio of 80%. A very strong spontaneous coupling efficiency of $7.5\times {10}^{-2}$ was measured.

GaN-based light-emitting diodes (LEDs) with emitting wavelength of 450 nm were grown on patterned sapphire substrates (PSSs) fabricated by chemical wet etching. The crystallography-etched facet was {1-102} R-plane with a 57deg against {0001} C-axis and had superior capability for enhancing light extraction efficiency. The light output power of the PSS LED was 1.15 times higher than that of the conventional LED at an injection current of 20 mA. The output power and external quantum efficiency were estimated to be 9 mW and 16.4%, respectively. The improvement was attributed not only to geometrical shapes of {1-102} crystallography-etched facets that efficiently scatter the guided light to find escape cones, but also to dislocation density reduction by adopting the PSS growth scheme

A graded-composition electron blocking layer (GEBL) with aluminum composition increasing along the [0001] direction was designed for c-plane InGaN/GaN light-emitting diodes (LEDs) by employing the band-engineering. The simulation results demonstrated that such GEBL can effectively enhance the capability of hole transportation across the EBL as well as the electron confinement. Consequently, the LED with GEBL grown by metal-organic chemical vapor deposition exhibited lower forward voltage and series resistance and much higher output power at high current density as compared to conventional LED. Meanwhile, the efficiency droop was reduced from 34% in conventional LED to only 4% from the maximum value at low injection current to $200\text{A}/{\text{cm}}^2$ .

We investigated the electroluminescence and relatively external quantum efficiency (EQE) of m-plane InGaN/GaN light emitting diodes (LEDs) emitting at 480 nm to elucidate the droop behaviors in nitride-based LEDs. With increasing the injection current density to $100\text{A}/{\text{cm}}^2$ , the m-plane LEDs exhibit only 13% efficiency droop, whereas conventional c-plane LEDs suffer from efficiency droop at very low injection current density and the EQE of c-plane LEDs decrease to as little as 50% of its maximum value. Our simulation models show that in m-plane LEDs the absence of polarization fields manifest not only the hole distribution more uniform among the wells but also the reduction in electron overflow out of electron blocking layer. These results suggest that the nonuniform distribution of holes and electron leakage current due to strong polarization fields are responsible for the relatively significant efficiency droop of conventional c-plane LEDs.

We report on the room temperature polariton lasing and photon lasing in a ZnO-based hybrid microcavity under optical pumping. A series of experimental studies of the polariton lasing (exciton-photon detunings of δ = −119meV) in the strong-coupling regime are discussed and compared to a photon lasing (δ = −45meV) in the weak-coupling regime obtained in the same structure. The measured threshold power density (31.8kW/cm²) of polariton lasing is one order of magnitude lower than that of the photon lasing (318.2kW/cm²). In addition, the comparison between polariton lasing and photon lasing is done in terms of the linewidth broadening, blue-shift of the emission peak, and polarization.