PL Mechanism Research Articles

Investigations of 1.55-μm GaInNAs/GaAs heterostructures by optical spectroscopy

Dilute nitride semiconductors are a topic of major current research interest owing to the novel physics induced by the incorporation of N in small percentages of composition. Related research has been further motivated by the favourable characteristics for device applications of the resultant materials, particularly represented by GaInNAs quaternary compounds as active materials in the 1.3–1.6 μm wavelength range. Whilst 1.3-μm GaInNAs/GaAs materials and devices are now reaching a level of maturity, the extension of these structures to around 1.55 μm is still in its infancy. The authors report optical studies of 1.55-μm GaInNAs/GaAs heterostructures of varying characteristics, all grown by molecular beam epitaxy. As the addition of N complicates the local structure and optical properties in this material system, the PL mechanisms are clarified by detailed PL excitation (PLE) spectra. Whereas all the measured samples exhibit strong PL at room temperature, the electronic structure is quite different between samples grown under different conditions. Some demonstrate clearly standard 2-D quantum well (QW) electronic states and some demonstrate evidence of phase-separated quantum-dot-like (QD) structures.

The fabrication and optical properties of highly crystalline ultra-long Cu-doped ZnOnanowires

We demonstrate the bulk synthesis of single crystalline Cu-doped ZnO nanowires using(CuI+ZnI2) powdersat 600 °C. These mass nanowires are characterized through x-ray diffraction, scanning electronmicroscopy, energy dispersive x-ray spectroscopy, transmission electron microscopy(TEM), selected area electron diffraction, and high-resolution TEM; they haveuniform diameters of about 65 nm and are several tens of microns in length. Thegrowth of ZnCuO nanowires is suggested for self-catalyzed vapour–liquid–solid. Inparticular, the PL spectra of these nanowires show emission peaks that strongly shiftto long wavelength with increasing Cu, and the doping quantity is found to beresponsible for the different characteristics; the PL mechanism is explained in detail.

Si Wire Light Emission Changes During Si/SiOx Interface Formation

ABSTRACTPhotoluminescence (PL), PL excitation, Raman scattering, IR absorption spectra as well as PSi surface morphology, have been studied as a function of Si/SiOx interface formation during PSi ageing in ambient air with the aim to reveal a PL mechanism. It is shown that fresh- prepared PSi layers created at low values of the anodization current Ia is characterized by “red” emission band centered at 1.72 eV, while the samples prepared at higher values of Ia have “orange” PL band centered at 2.00 eV. During oxidation in ambient air two processes take place at the PSi ageing: the oxidation of small size Si nano-crystallites up to their disappearing and the change of silicon oxide composition at the Si/SiOx crystallite surface. These processes initiate changes in PL and PL excitation spectra. The peak position of “red” PL band shifts to the high-energy up to 1.80-1.85 eV while the “orange” band does not change essentially.

Ge Nanocrystal Formed Directly by High-Dose-Ion-Implantation and the Related UV-VIS Photoluminescence

ABSTRACTThe investigation of nanocrystalline Ge (nc-Ge) directly prepared with high dose Ge ion implantation of 1×1016, 1×1017, 5×1017and 1×1018cm-2respectively without subsequent annealing is presented in this paper. The specimens were measured by means of GIXRD, LRS and PL. The results show the nc-Ge, which possesses strong compressive stress, can be fabricated when the implanting dose of Ge ions is over the threshold dose∼1×1017cm-2. The content and size of nc-Ge will enlarge with increasing dose. The nc-Ge formation mechanism may be the Ge atoms in the amorphous Ge (a-Ge) clusters, which are formed through the aggregation of implanted Ge ions, obtain energy from the instant local annealing zone induced by the incident Ge ion and reconstruct to nc-Ge existing in a-Ge clusters. The PL results indicate the strong PL peaks centered at about 295, 400 and 570 nm can be observed in implanted samples. The intensity of these PL peaks increases with increasing dose. The related PL mechanism in Ge-ion-implanted SiO2film has also been discussed.

Photoluminescence effect of Ru dye on alumina membranes with ordered pore arrays

We have investigated the quenching luminescence and the luminescence mechanisms of self-assembled Ru(II)L2X2 (Ru(II)(4,4’-dicarboxyl-2,2’-bipyridyl)2(SCN)2) dye in porous anodic alumina. Porous anodic alumina can emit visible light due to numerous oxygen vacancies formed during anodic oxidation. Energy transfer from the porous anodic alumina to the dye molecules causes the quenching and red shift of the PL peak, which gives a fundamental understanding of the PL mechanism in porous anodic alumina.

A study on photoluminescence from Si-rich silicon oxide films and Ge-containing silicon oxide films

Si-rich silicon oxide films and Ge-containing silicon oxide films were deposited using the RF magnetron sputtering technique with a Si–SiO 2 and a Ge–SiO 2 composite target, respectively. The percentage area ratio of Si to SiO 2 was 30%, and that of Ge to SiO 2 was 10%. These films were annealed in a N 2 ambient at 300°C, 600°C, 900°C, 1000°C or 1100°C for 30 min. All the PL spectra from the two types of films annealed at various temperatures have similar shapes with peak positions around 580nm (~2.1 eV). Annealing at 900°C or 1100°C, crystalline nanometer silicon particles (NSPs) in the Si-rich silicon oxide films and annealing at 900°C crystalline nanometer Ge particles (NGPs) in Ge-containing silicon oxide films can be observed using a high-resolution transmission electron microscope (HRTEM). The PL peak positions for Si-rich silicon oxide films do not show any correlation with the sizes of crystalline NSPs, and PL intensity does not show any correlation with the density of crystalline NSPs. The PL peak positions of both types of films do not show any shift when measurement temperature increases from 10 to 300 K. The PL mechanisms for the Si-rich silicon oxide films and Ge-containing silicon oxide films have been discussed.

PL due to Discrete Gap Levels in Some Chalcogenide Glasses- A Configurational Coordinate Diagram Illustration

ABSTRACTPhotoluminescence (PL) studies were carried out on a-Se and a few Ge20Se80−xBix and Ge20Se70−xBixTe10 bulk glassy semiconductors at 4.2 K with Ar+ laser as excitation source. While a-Se and samples with lesser at% of Bi show fine structured PL with a large Stokes shift, samples with higher at% of Bi did not show any detectable PL. The investigations show at least three radiative recombination transitions. Features extracted by deconvoluting the experimental spectra show that the discrete gap levels associated with the inherent coordination defects are involved in the PL transitions. Absence of PL in samples with higher Bi at% are explained on the basis of nonradiative transition mechanisms. Overall PL mechanism involving gap levels in chalcogenide glasses is illustrated with the help of a configurational coordinate diagram.

Observation of Band Gap Energy Fluctuation of Microcrystalline InGaN:Zn

ABSTRACTThis paper describes a comparison of the optical properties of InGaN:Zn with that of GaN:Zn and InGaN by measuring photoluminescence excitation (PLE) spectra at 77 K. It is well known that MOCVD grown InGaN films tend to have a fluctuation in In concentration which results in a fluctuation of the band gap energy. The PL mechanism in InGaN films has been assigned to the annihilation of an exciton at the potential minima caused by the fluctuated band gap potential. We grew InGaN(:Zn) and GaN:Zn microcrystals emitting intense blue luminescence by a reaction of GaN and In2S3 with NH3 in the range of 850 to 900 °C. The samples grown at various temperatures show two PLE peaks: one weak peak is located around 3.47 eV, which we attribute to the band gap energy, and the other peak around 3.15 eV, which we attributed to the In localized state level. We had proposed an atomic structure of the localized state based on an isoelectronic trap theory. However, it is necessary to estimate the order of potential fluctuation of the grown InGaN microcrystal is small in order to assure the isoelectronic trap theory. PLE spectra of InGaN:Zn were measured and compared with that of GaN:Zn to estimate the degree of energy gap fluctuation. As the shape of a PLE peak of InGaN:Zn at around 3.47 eV was comparable to that of GaN:Zn, we concluded that the isoelectronic trap model holds for the grown InGaN microcrystals.

Gas-source molecular beam epitaxial growth of SiGe alloy-based `naked' quantum wells

We report the molecular beam epitaxialgrowth and photoluminescence of Si 1− x Ge x /Si alloy-based `naked' quantum wells (QWs). The PL stability and anomalous spectral modulation characteristic of naked QWs are discussed in the context of surface morphological change. Experimental findings as well as theoretical calculations suggest that the in-plane exciton localization rather than perpendicular confinement due to the surface barrier dominates the PL mechanism of naked QWs.

Porous silicon photoluminescence: type II-like recombination mechanism

The Letter proposes a model to explain the PL mechanism in porous silicon. It was inspired by type II semiconductor interface PL behaviour. In this model, the PS radiative recombinations involve energy levels in the silicon oxide layer. This model takes into account quantum confinement and the energy threshold above which PS PL is observed.