Improvements of the internal quantum efficiency by reduction threading dislocation density and light extraction using UV transparent p-type cladding contact layers, reflecting ohmic contact, chip encapsulation with optimized shape refractive index allowed us to obtain external 10.4% at 20 mA CW current output power up 9.3 mW 278 nm for AlGaN-based deep-ultraviolet light-emitting diodes grown on sapphire substrates.

Femtosecond laser pulses generate in Sb coherent ${E}_{g}$ phonons at $\ensuremath{\approx}3.4\mathrm{THz}$, addition to oscillations of ${A}_{1g}$ symmetry accounted for by the phenomenological displacive-excitation model. Experiments agree with theoretical calculations showing that driving force absorbing materials like is determined Raman processes, as transparent media. The formalism provides a unifying approach describing light-induced motion atoms both impulsive and displacive character.

In this letter, the achievement of over 60 mW output power from pseudomorphic ultraviolet light-emitting diodes in continuous wave operation is reported. Die thinning and encapsulation improved photon extraction efficiency to 15%. Improved thermal management a high characteristic temperature resulted low rolloff up 300 mA injection current with an 67 mW, external quantum (EQE) 4.9%, wall plug (WPE) 2.5% for single-chip device emitting at 271 nm operation.

We present the analysis of external quantum efficiency in AlGaN deep ultraviolet (DUV) light-emitting diodes (LEDs) on sapphire substrates and discuss factors affecting output power DUV LEDs. Performance LED is related to optimization device structure design improvements epitaxial material quality.

Femtosecond laser pulses and coherent two-phonon Raman scattering were used to excite KTaO3 into a squeezed state, nearly periodic in time, which the variance of atomic displacements dips below standard quantum limit for half cycle. This nonclassical state involves continuum transverse acoustic modes that leads oscillations refractive index associated with frequency van Hove singularity phonon density states.

Optically pumped ultraviolet lasers were fabricated on low-defect-density bulk (0001) AlN substrates. AlxGa1-xN/AlyGa1-yN heterostructures grown by metal–organic vapor phase epitaxy near atmospheric pressure. Time-resolved photoluminescence studies of the multiple quantum well emission show long decay times 900 ps at room temperature and confirm high structural quality epitaxial layers. Laser resonators with a length about 1 mm formed cleaving crystal to obtain m-plane mirror facets. Lasing...

AlGaN samples grown by plasma-assisted molecular-beam epitaxy on sapphire (0001) substrates, with 20%–50% Al content and without the use of indium, show intense room-temperature photoluminescence that is significantly redshifted, 200–400meV, from band edge. This emission characterized a long lifetime (∼375ps) comparable to seen in low defect density (∼108cm−2) GaN. Room-temperature monochromatic cathodoluminescence images at redshifted peak reveal spatially nonuniform similar observed...

Lifetime measurements on single-chip, packaged 285 nm light-emitting diodes (LEDs) performed under constant current injection at 20 and 75 mA, were compared to the performance of unbiased LEDs baked equivalent operating junction temperatures. The thermally stressed devices showed a lesser degradation than those electrically stressed, indicating that elevated temperature alone does not cause degradation. Despite decay less half initial power injection, time-resolved photoluminescence active...

Abstract Sub‐300 nm optically pumped ultraviolet lasers were realized on low‐defect‐density (0001) AlN substrates fabricated from single crystalline boules. The Al x Ga 1– N/Al y N hetero‐structures grown by metal‐organic vapor phase epitaxy near atmospheric pressure. high structural quality of the pseudomorphically deposited films was confirmed X‐ray reciprocal space mappings and time‐resolved photoluminescence (PL) studies multiple quantum well emission. initial PL‐decay times for a sample...

We demonstrate that high‐Al content ( x > 0.6) Al Ga 1− N films grown in the III‐rich regime by plasma‐assisted molecular beam epitaxy at elevated growth temperatures, ≥900 °C, possess strong, red shifted room temperature (RT) photoluminescence (PL) correlated with presence of lateral nanoscale periodic oscillations composition. As increased from 800 to 900 additional peaks PL spectrum appear ≈275–280 nm and ≈250–255 nm, strongly fundamental absorption edge ≈240 nm. This is characterized...

Abstract Single quantum wells of low InN concentration InGaN grown on high quality nonpolar and semipolar substrates cut from bulk GaN boules are studied by time‐resolved photoluminescence techniques. Data is presented for different well widths at varying pump fluence sample temperature to study nonlinear non‐radiative recombination, radiative lifetimes, carrier localization or separation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pump-probe measurements of coherent-phonon-induced changes refractive index in LaAl${\mathrm{O}}_{3}$ are dominated by normally weak boundary effects. Atomic displacements the range 50--500 $\ensuremath{\mu}\AA{}$ were generated and probed femtosecond laser pulses through impulsive Raman scattering. The absence a bulk contribution is ascribed to phase mismatch due domain disorder. Selection rules consistent with model considering reflection transmission at interfaces. Intensities phonon...

Temperature-dependent photoluminescence (PL) lifetimes were measured for a series of ultra-thin c-plane Al0.61Ga0.39N/AlN multiple quantum wells (QWs) on bulk AlN substrates with the well thickness varying from 0.6 to 2 nm. At temperatures below 75 K, estimates internal efficiency indicate that recombination is primarily radiative, lifetime ∼160 ps nm QWs, comparable low temperature PL observed in AlGaN films similar Al content. This short despite presence layer fluctuations and...

We study the phase-dependent structural and electronic properties of bulk LaPO4, using density functional theory (DFT). The applicability conventional semi-local hybrid functionals in predicting monoclinic hexagonal LaPO4 is evaluated by comparing results to available experimental data. was found be more stable than phase ambient conditions with a small energy difference, suggesting possibility transition. Both phases form are diamagnetic indirect gaps. These consistent results. In phase,...

We have simultaneously excited a coherent and squeezed phonon field in SrTiO3 using femtosecond laser pulses stimulated Raman scattering. The frequency of the state (a 1.3 THz) is that A1g-component soft mode responsible for cubic-tetragonal phase transformation at approximately 110 K. involves continuum transverse acoustic phonons dominated by narrow peak density states 6.9 THz.

This article describes defect reduction mechanisms that are active during the growth of GaN by nanoheteroepitaxy on (0001) 6H SiC. Nanoheteroepitaxial (NHE) and planar epitaxial films were grown compared using transmission electron microscopy, photoluminescence, x-ray diffraction, time resolved photoluminescence. It was found in addition to previously reported mechanism results from high compliance nanoscale nuclei, other independent also NHE including: (i) filtering substrate defects, (ii)...

Abstract Temperature dependent time‐resolved photoluminescence is used to study the development of active regions for optoelectronic devices employing AlGaN nanostructures deep‐UV emission. The changing importance dislocation versus point defects and their relationship different forms carrier localization are discussed. results presented suggest that nanostructure emitters require both defect/impurity suppression improved efficiency lower density interface quality. (© 2010 WILEY‐VCH Verlag...

While it is well known that high quality III–nitride material deposited by plasma-assisted molecular beam epitaxy (PA-MBE) only under III-rich conditions, the extent of III-flux required for optimal film growth unclear. In this article, we focus on dependence optical properties III/V flux ratio. Specifically, report photoluminescence (PL) intensity and lifetime photogenerated carriers in homoepitaxially grown GaN films, Ga-rich as a function Ga employed during growth. The samples...

Optical and electronic properties of mid-ultraviolet light emitting diodes with a two-step p-AlGaN region are measured at temperatures from 8 to 300 K. While the electroluminescence intensity increases down temperature lower than that reported in InGaN (LEDs), there is still collapse cryogenic temperatures. Capacitance-voltage measurements across same range reveal an increasing depletion decreasing indicating hole injection significant factor dependent behavior, as well cause collapse.