We investigate the mechanism of light extraction enhancement of a GaN-based light-emitting diode (LED) grown on patterned sapphire substrate (PSS), that has ZnO nanorod arrays (NRAs) fabricated on top of the device using the hydrothermal method. We found that the light output power of the LED with ZnO NRAs increases by approximately 30% compared to the conventional LED without damaging the electrical properties of the device. We argue that the gradual decrease of the effective refractive index, which is caused by the fabrication of ZnO NRAs, is the mechanism of the observed improvement. Our argument is confirmed by cross-sectional confocal scanning electroluminescence microscopy (CSEM) and the theoretical simulations, where we observed a distinct increase of the transmission at the interface between LED and air at the operation wavelength of the LED. In addition, the plane-view CSEM results indicate that ZnO NRAs, which were grown on the bare p-type GaN layer as an electrical safety margin area, also contribute to the enhanced light output power of the LED, which indicate further enhancement is manifested even in the optically ineffective sacrificial area.

The authors demonstrate a simple method to achieve local tuning of optical modes in GaAs photonic crystal nanocavities by continuous wave laser-assisted oxidation in air atmosphere. By irradiation with a focused laser beam at power levels of a few tens of milliwatts, photonic crystal nanocavity modes shift to shorter wavelengths by up to 2.5 nm. The mode shifts can be controlled either by varying the laser power or by iterating laser-assisted oxidation steps and are well explained by finite-element-method and finite-difference time-domain simulations. This method provides a simple route to achieve fine spectral tuning of individual nanocavities for photonic devices.

We used low-temperature reactions to synthesize different-sized CdSe quantum dots (QDs) capped with fatty-acid and phosphine ligands. From the correlation of high-resolution transmission electron microscopy and X-ray diffraction (XRD) analyses of the synthesized QDs, we observed size-dependent shape anisotropy. In addition, the recorded XRD patterns revealed mixed crystal facets with zinc blende and wurtzite structures in small-sized QDs. Furthermore, from differential absorption (DA) spectra, we extracted the electronic transition energies for different-sized QDs, which were found to be similar to the calculated values of the quantum size levels associated with band mixing of CdSe QDs with a moderate bandgap. We found that the excitonic absorption peaks are increasingly “hidden” with decreasing QD size because of the crystal structure and crystalline quality. The results show good agreement with the obtained diffraction patterns and the estimation errors obtained from the DA spectra.

We synthesized CsPbBr₃ perovskite nanocrystals (NCs) at different reaction temperatures and tracked their growth kinetics on the basis of their optical properties and estimated size. The energies of the absorption and fluorescence (FL) peaks with increasing reaction temperature for the CsPbBr₃ perovskite NCs were tuned within the regions of 2.429–2.570 eV and 2.391–2.469 eV, respectively, depending on size of the NCs (9.9–12.5 nm). The Stokes shifts of CsPbBr₃ perovskite NCs with increasing NC size decreased from 101 meV to 38 meV. The full-width at half-maximum of the FL peaks for the CdSe NCs decreased from 150 meV to 90 meV because of the improved size uniformity of the CsPbBr₃ perovskite NCs. The energy spacing of CsPbBr₃ perovskite NCs synthesized at various reaction temperatures was calculated from Tauc plots; this information is critical for determining the bandgap energy and enables the size of the CsPbBr₃ perovskite NCs to be estimated using the effective mass approximation.

The influence of the growth conditions of multilayer CdTe/ZnTe quantum dots (QDs) on Si substrate upon their carrier dynamics is studied using intensity integration and broadening photoluminescence. The unusual temperature dependence of the line broadening is explained using a model for interband transitions that involves a lowest discrete electronic state (1S_e) with different discrete hole states (1S_3/2 and 2S_3/2) and a 1P transition. These transitions are expected to play a critical role in both the thermally activated energy and the line broadening of the QDs. We also demonstrate that a thermally activated transition between two different states occurs with band low-temperature quenching, with values separated by 5.8–16 meV. The main nonradiative process is thermal escape assisted by carrier scattering via emission of longitudinal phonons through the hole states at high temperature, with an average energy of 19.3–20.2 meV.

Temperature-dependent photoluminescence measurements showed that the activation energy of CdTe/ZnTe quantum dots (QDs) coupled with a quantum well is much larger than that of the QDs alone, This behavior is attributed to the tunneling of carriers via a thin separation layer from the quantum well to the QDs. The present observations can help improve understanding of the enhancement of the activation energy in coupled CdTe/ZnTe nanostructures.