Semiconductor Photonics: Nano-Structured Materials and Devices

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Authors: M.J. Chiang, C.W. Wu, H.E. Cheng
Abstract: Copper oxide, a direct band gap semiconductor with band gap about 1.21-1.51 eV, has been regarded as a promising material for photovoltaic. Nanocrystalline copper oxide films have been synthesized on Si by dc sputtering method. The effects of oxygen flow rate and deposition temperature on the microstructure of nanocrystalline copper oxide films were investigated. X-ray diffraction analysis shows that a broaden peak of Cu2O (111) at 36.720 was observed at the deposition condition of DC power 150 W, pressure 2*10-2 Torr, substrate temperature 100 °C, Ar flow rate 15 sccm and O2 flow rate 1sccm. With increasing the oxygen flow rate to 3 and 5 sccm, CuO (-111) could be observed at 36.58o. The increase of oxygen flow rate resulted in the film formation from Cu2O to CuO. SEM pictures show that copper oxide films exhibit nanosize grains. X-ray diffraction patterns of CuO films deposited at 50~200 °C show that only (-111) plane is obtained. The SEM pictures show that the grain size increases with the deposition increases.
Authors: P. Boonpeng, S. Panyakeow, S. Ratanathammaphan
Abstract: InAs quantum dots (QDs) have been grown by solid-source molecular beam epitaxy on different InxGa1-xAs (0 ≤ x ≤ 0.3) to investigate the effect of In-mole-fraction and thickness of InGaAs insertion layer (IL) on the structural and optical properties of the QDs. The density of QDs directly grown on GaAs is 1×1010 cm-2, and increase to 1.4-1.8×1010 cm-2 on InGaAs layers which depend on the In-mole-fraction and thickness of InGaAs layers. The effects of In-mole-fraction and thickness of InGaAs insertion layer on optical properties of the QDs are studied by photoluminescence (PL). The FWHM of PL spectrum corresponds to the size distribution of the QDs.
Authors: H. Choi, H.K. Kim, Y.W. Koo, K.H. Nam, S.M. Koo, W.J. Cho, H.B. Chung
Abstract: Programmable metallization cell (PMC) memory is based on the electrochemical control of nanoscale quantities of metal in thin films of solid electrolyte. We investigate the nature of thin films formed by the photo-dissolution of Ag into Ge-Se-Te glasses for use in programmable metallization cell devices. Glassy alloys of a-Ge25Se75-xTex(x = 0, 25) are prepared by well known melt-quenching technique. Thin films of a-Ge25Se75-xTex(x = 0, 25) glassy alloys are evaporated by vacuum evaporation technique at ~10-6 torr on glass substrate at room temperature. Optical properties in this study concerns photo-diffusion of Ag on Ag-doped Ge-Se-Te electrolytes. With these promising properties, the composition a-Ge25Se75-xTex(x = 0, 25) is recommended as a potential candidate for PMC-RAM.
Authors: Xiao Song Zhang, Xiao Yi Dong, Gui Yun Kai, Dong Qing Dong, Yan Fang Zhang, Zhi Wang
Abstract: ZnS:Er quantum dots were prepared in the aqueous medium from readily available precursors. The construction, morphology and luminescence properties of the ZnS:Er quantum dots were evaluated by XRD,TEM and photoluminescence spectra. Furthermore, the 1590 nm emission of the ZnS:Er quantum dots excited by a 785.0 nm NIR laser were discussed.
Authors: Hannah C. Gardner, Birju Patel, Cristina Bertoni, Diego E. Gallardo, Steve Dunn
Abstract: Nanostructured CdTe is proving a popular material for a variety of modern applications. Here, we report photoluminescent deterioration of CdTe due to Cl2 contamination. Cl2 gas was bubbled through a 2ml suspension of thioglycolic acid capped CdTe nanoparticles whilst photoluminescence was monitored. With the addition of only 0.02ml of Cl2 a loss of luminescence intensity was observed. Addition of 0.4ml of Cl2 resulted in a 70% loss of luminescence intensity, a 21nm shift in wavelength, and a large narrowing of the full-width-at-half-maximum. Cl2 attacks the Cd-S bond in the thiol capping layer of the nanoparticle, disrupting the passivation of the nanocrystal, and allowing the formation of non-radiative trap states. Smaller nanocrystals with a larger surface area to volume ratio are more heavily affected as is shown in the selective reduction of intensity from the smaller particles resulting in a narrower full-width-at-half-maximum and an apparent photoluminescence shift. A decrease in overall intensity is seen due to the lower number of emitting particles.
Authors: M. Singh, J.S. Arora, Kamlendra Awasthi, R. Nathawat, Y.K. Vijay
Abstract: The Zn-Se bilayer structure prepared using thermal evaporation method at pressure 10-5 Torr. These films annealed in the vacuum for two hours on different constant temperatures. The optical band gap was found to be varying with annealing temperature due to removal of defects and increase in grain size. It was also observed by the X-ray diffraction pattern the grain size of the film increase with annealing temperature. The lattice constant of hexagonal structure of these films is found to be a =b=4.42Å and c=5.68Å. The dominant peaks to be at 23.2°,28° and 43.9° having values (100), (002) and (111) respectively. The Rutherford back scattering data of these films confirmed the mixing of elements with time.
Authors: W. Jewasuwan, S. Panyakeow, S. Ratanathammaphan
Abstract: We report on the fabrication of self-assembled InP ring-shape nanostructures on In0.49Ga0.51P by droplet molecular-beam epitaxy. The dependency of InP ring-shape nanostructural properties on substrate temperature and indium deposition rate is investigated by ex situ atomic force microscope (AFM). The nano-craters are formed when indium deposition at 120°C while the ring shape quantum-dot molecules are formed when indium deposition at 150°C or higher. The size, density and pattern of InP ring-shape nanostructures strongly depend on substrate temperature and indium deposition rate during indium deposition.
Authors: A. Verma, P.K. Bhatnagar, P.C. Mathur, S. Nagpal, P.K. Pandey, J. Kumar
Abstract: Quantum Dots (QDs) of CdSxSe1-x embedded in borosilicate glass matrix (BGM) have been grown using colored glass filter (RG695). Double-Step (DS) annealing method was adopted in which nucleation is achieved at a lower temperature (475°C) without any crystallization. To obtain crystallization on these nucleation centers, the annealing temperature is raised to 575°C at which the nucleation rate is negligible. QDs of various average radii and volume fractions are grown by varying the annealing duration from 3 to 11hrs. QDs corresponding to higher annealing duration are found to have low size dispersion (SD) and high volume fraction but weak quantum confinement, while, the QDs corresponding to lower annealing durations have high quantum confinement due to their much lower radii as compare to Bohr exciton radius, their SD is high and volume fraction low. For nonlinear optical applications the SD must be low and volume fraction should be high. Attempt has been made to optimize the two parameters. Further it has been concluded that there is no contribution of the band edge recombination to the PL and the origin of the PL is due to shallow traps existing in the volume of the QDs. Studies of absorption and PL have also been made on the samples aged for 18, 24 and 36 months. It is found that the effect of aging is to increase the absorption coefficient, reduce the shallow trap centers and reduce the SD.
Authors: Rita John
Abstract: The first principle investigations on electronic structure of ABC2 (A = Cd; B = Si, Ge, Sn; C= P, As) pnictides using the Tight Binding Linear Muffin Tin Orbital (TB-LMTO) method within the Atomic Sphere Approximation (ASA) is reported. Variation of Eg with pressure reveals the direct and pseudodirect natures of these compounds. CdSiP2 shows a pseudo direct and CdGeP2, CdSnP2, CdSiAs2, CdGeAs2 and CdSnAs2 show direct band gap natures. Semiconductor to metal transition at high pressures is observed. Metallisation volumes (V/Vo) m and pressures (Pm), bulk modulus (Bo) and its pressure derivative (Bo 1) are reported. Correlation connecting Bo and the unit cell volume (Vo) is established.

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