1,721,008 research outputs found
Dilute nitride III-V nanowires for high-efficiency intermediate-band photovoltaic cells: Materials requirements, self-assembly methods and properties
No full textThis paper deals with dilute nitride III-V (III-N-V) semiconductor nanowires and their synthesis by bottom-up (so-called self-assembly) methods for application to novel and high efficiency intermediate-band solar cells (IBSCs). Nanowire-IBSCs based on III-N-V compounds promise to overcome many of the limitations encountered so far in quantum-dots or planar-heterostructure IBSCs; indeed, thanks to the combination of IBSC functionality with the unique physical properties associated with nanowires-based devices, photovoltaic cells with unprecedentedly high power conversion efficiency, simpler junction geometry, reduced structural constraints, low materials usage and fabrication costs could be conceived. The fabrication of III-N-V nanowire-IBSCs requires however, careful engineering of the inner nanowire-device structures to comply with both IBSC stringent operational requirements and the peculiar physical properties of III-N-V semiconductor alloys. Herewith, we propose for the first time perspective III-N-V core-multishell nanowire heterostructures as potential candidates to IBSC applications, their fabrication requiring however, precisely controlled self-assembly technologies. The present status of research on the topic is reviewed, focusing in particular on the bottom-up growth of III-N-V nanowires by molecular beam and metalorganic vapor phase epitaxy methods and properties of as-grown nanostructures. Major results achieved in the current literature and open problems are presented and discussed, along with advantages and limitations of employed self-assembly methods for the fabrication of dilute nitride III-V based nanowire-IBSCs
Adsorption and decomposition steps on Cu(111) of liquid aromatic hydrocarbon precursors for low-temperature CVD of graphene: A DFT study
No full textLow-temperature chemical vapor deposition (LT-CVD) of graphene using liquid aromatic hydrocarbons holds technological advantages over conventional growth from methane. However, the nature of decomposition mechanisms of such precursors and their effectiveness in a LT-CVD process is still debated. We investigate by means of density functional theory adsorption energies and decomposition first steps on Cu(111) of single-ring aromatic hydrocarbons, such as benzene and toluene. Our results confirm the stronger stability with respect to methane of aromatic adsorbates, due to exchange of London dispersion forces with Cu surface; however, toluene exhibits improved bindings with respect to benzene. The adsorption energy slightly improves if additional methyl groups are substituted in benzene, as in o-xylene and 1,2,3-trimethylbenzene. Among decomposition reactions, dehydrogenation of the methyl group in toluene is energetically more favored (1.20 eV) than that of methane (1.52 eV) or aromatic C-rings (1.67 eV and 1.72 eV for benzene and toluene), while demethylation of toluene remains negligible due to the prohibitive energy barrier (2.49 eV). Methyl dehydrogenation in toluene leads to the abundant formation of adsorbed benzyl radicals onto Cu in an almost parallel-to-surface configuration, as active species for graphene nucleation. Toluene (and to a lesser extent o-xylene and 1,2,3-trimethylbenzene) should be thus preferred to benzene in LT-CVD of graphene
"Surface structural and morphological characterization of ZnTe epilayers grown on {100} GaAs by MOVPE"
No full textStructural and optical properties of MOVPE-grown ZnMgSe epilayers and ZnSe/ZnMgSE multiple quantum wells
No full textLattice strain and band offset determination in ZnSe/ZnS short -period superlattices grown by MOVPE on (001)GaAs
No full textLattice Strain Relaxation and Compositional Control in As-Rich GaAsP/(100)GaAs Heterostructures Grown by MOVPE
Full text linkThe fabrication of high-efficiency GaAsP-based solar cells on GaAs wafers requires addressing structural issues arising from the materials lattice mismatch. We report on tensile strain relaxation and composition control of MOVPE-grown As-rich GaAs1−xPx/(100)GaAs heterostructures studied by double-crystal X-ray diffraction and field emission scanning electron microscopy. Thin (80–150 nm) GaAs1−xPx epilayers appear partially relaxed (within 1−12% of the initial misfit) through a network of misfit dislocations along the sample (Formula presented.) and (Formula presented.) in plane directions. Values of the residual lattice strain as a function of epilayer thickness were compared with predictions from the equilibrium (Matthews–Blakeslee) and energy balance models. It is shown that the epilayers relax at a slower rate than expected based on the equilibrium model, an effect ascribed to the existence of an energy barrier to the nucleation of new dislocations. The study of GaAs1−xPx composition as a function of the V-group precursors ratio in the vapor during growth allowed for the determination of the As/P anion segregation coefficient. The latter agrees with values reported in the literature for P-rich alloys grown using the same precursor combination. P-incorporation into nearly pseudomorphic heterostructures turns out to be kinetically activated, with an activation energy EA = 1.41 ± 0.04 eV over the entire alloy compositional range
GaAs hetero-epitaxial layers grown by MOVPE on exactly-oriented and off-cut (1 1 1)Si: Lattice tilt, mosaicity and defects content
Full text linkIntegration of III-V devices with Si-photonics and fabrication of monolithic III-V/Si tandem solar cells require the heteroepitaxy of III-V compounds on Si. We report on the lattice tilt, mosaicity and defects content of relaxed GaAs grown by MOVPE on exactly-oriented and 4°-offcut (1 1 1)Si. Thin GaAs single-layers grown at 400 °C and annealed at 700 °C show ∼ 3×10^8 cm−2 density of surface pinholes. Double-layer samples were obtained by GaAs overgrowth at 700 °C. GaAs epilayers are tilted by (0.05–0.14)° with respect to Si. Rotational twins were observed in X-ray diffraction (XRD) pole figures: the most abundant ones originate from 60°-rotation of GaAs around the [1 ̄1 ̄1 ̄] growth direction and are identified as micro-twins along the GaAs/Si hetero-interface. Twins obtained by rotations around the [1 ̄1 ̄1], [11 ̄1 ̄], and [1 ̄11 ̄] directions or by combined rotations around the growth direction and one of the former, were also observed. The GaAs mosaicity and block size were studied through high-resolution XRD intensity mapping: for single-layer samples crystal blocks are ascribed to 3–5 nm thin micro-twins, whose size does not change upon annealing. In double-layer samples thicker (32–35 nm) micro-twins occur. GaAs samples grown on offcut (1 1 1)Si show less rotational twins but a reduced mosaic block size with respect to exactly-oriented Si
Crystalline structure of ZnSSe epilayers grown on (100)GaAs by metaorganic vapour-phase epitaxy
No full textInhomogeneous strain relaxation and detect distribution of ZnTe layers deposited on (110)GaAs by metalorganic vapor phase epitaxy (vol 78, pg 229, 1995)
No full textLOEQInfm lecce,unita gnsm,i-73100 lecce,italy. ecole polytech fed lausanne,inst micro & optoelectr,ch-1015 lausanne,switzerland. cnr,ime,inst mat elettron,i-73100 lecce,italy. univ padua,dipartimento fis g galilei,i-35100 padua,italy. infm padova,unita gnsm,i-35100 padua,italy. Lovergine, N, UNIV LECCE,DIPARTIMENTO SCI MAT,VIA ARNESANO,I-73100 LECCE,ITALY.ISI Document Delivery No.: TN211Cited Reference Count: 1Cited References:LOVERGINE N, 1995, J APPL PHYS, V78, P22
- …
