Photoluminescence (PL) properties of InN dots embedded in GaN were investigated. We observed a systematic blueshift in the emission energy as the average dot height was reduced. The widely size-tunable emission energy can be ascribed to the size quantization effect. Temperature-dependent PL measurements show that the emission peak energies of the dots are insensitive to temperature, as compared with that of bulk film, indicating the localization of carriers in the dots. A reduced quenching of the PL from the InN dots was also observed, implying superior emission properties for the embedded InN dot structures.
GaN quantum dots were grown on an Al(0.11)Ga(0.89)N buffer layer by using flow rate modulation epitaxy. The Stranski-Krastanov growth mode was identified by an atomic force microscopy study. The thickness of the wetting layer is about 7.2 monolayers. The temperature dependent photoluminescence studies showed that at low temperature the localization energy, which accounts for de-trapping of excitons, decreases with the reducing dot size. The decrease in emission efficiency at high temperature is attributed to the activation of carriers from the GaN dot to the nitrogen vacancy (V(N)) state of the Al(0.11)Ga(0.89)N barrier layer. The activation energy decreases with reducing dot size.
Several approaches have been employed to grow high-quality ZnSe epilayers on Ge∕Ge0.95Si0.05∕Ge0.9Si0.1∕Si virtual substrates. The ZnSe epilayers were characterized by photoluminescence spectroscopy. Migration enhanced epitaxy and inserting an in situ thermal annealing ZnSe buffer layer effectively reduced the intensity of deep level emissions from the ZnSe epilayer grown on a 6°-tilted Ge∕Ge0.95Si0.05∕Ge0.9Si0.1∕Si virtual substrate. Optimized conditions for growing high-quality ZnSe were used to deposit ZnCdSe∕ZnSe multiple quantum wells on Ge∕Ge0.95Si0.05∕Ge0.9Si0.1∕Si virtual substrates. Photoluminescence spectroscopy revealed quantum-confinement effect in the ZnCdSe multiple quantum wells. The evolution of the exciton emission peak energy and the linewidth as a function of temperature indicate a low density of localized sites in the sample with a well width of 1nm. In the high-temperature regime, the thermal quenching of the excitonic emission intensity from ZnCdSe quantum well structures was governed by the thermal activation of carriers from quantum-well-confined states into barrier states.
The substrate treatment with seeding promoter can promote the two-dimensional material lateral growth in chemical vapor deposition (CVD) process. Herein, graphene quantum dots (GQDs) as a novel seeding promoter were used to obtain uniform large-area MoS 2 monolayer. The obtained monolayer MoS 2 films were confirmed by optical microscope, scanning electron microscope, Raman and photoluminescence spectra. Raman mapping revealed that the MoS 2 monolayer was largely homogeneous.
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