Abstruct-The conduction mechanism and the origins of the leakage current in undoped channel polycrystalline silicon thin-film transistors fabricated under a variety of processing conditions were investigated. Leakage currents below 1 nA at drain-source voltages of 40 V were achieved in both n-type and p-type devices. The effective channel electron and hole mobilities were 75 and 42 cm2/Vs, respectively. Measured stage delay times for CMOS ring oscillators as a function of supply voltage agreed well with theoretical calculations. The effective carrier mobility was shown to have a minimum at a gate voltage corresponding to the point at which all traps are filled. Both dark and photo-induced leakage currents were determined to be controlled by generation from the grain boundary traps. The voltage drop across individual gates in multi-gated structures was investigated as a function of gate voltage. The use of multiple gates at high drain-source potentials was found to decrease both dark and photo-induced leakage currents.

To investigate the effect of growth area on interface dislocation density in strained-layer epitaxy, we have fabricated 2-.um-high mesas of varying lateral dimensions and geometry in (001) GaAs substrates with dislocation densities of 1.5 X 10\ 10 4 , and 10 2 cm--2 • 3500-, 7000-, and 8250-A-thick In o (J5 Gao 95 As layers, corresponding to 5, to, and 11 times the experimental critical layer thickness as measured for large-area samples, were then deposited by molecularbeam epitaxy. For the 3500-A layers, the linear interface dislocation density, defined as the inverse of the average dislocation spacing, was reduced from greater than 5000 to less than 800 em -I for mesas as large as 100 pm. A pronounced difference in the linear interface dislocation densities along the two interface (110) directions indicates that a dislocations nucleate about twice as much as /3 dislocations. For samples grown on the highest dislocation density substrates, the linear interface-dislocation density was found to vary linearly with mesa width and to extrapolate to a zero linear interface-dislocation density for a mesa width of zero. This behavior excludes dislocation multiplication or the nucleation of surface half"loops as operative nucleation sources for misfit dislocations in these layers. Only nucleation sources that scale with area (termed fixed sources) are active. In specimens with lower substrate dislocation densities, the density of interface dislocations still varies linearly with mesa size, but the slope becomes independent of substrate dislocation density, indicating that surface inhomogeneities now act as the dominant source for misfit dislocations. Thus, in 3500-A-thick overlayers, substrate dislocations and substrate inhomogeneities are the active fixed nucleation sources. Since only fixed nucleation sources are active, a single strained layer wiH dramatically reduce the threading dislocation density in the epilayer. For the 7ooo-A layers, we observe a superlinear increase in linear interface-dislocation density with mesa size for mesas greater than 200,um, indicating that dislocation mUltiplication occurs in large mesas. For mesas less than 200 pm in width, linear interface-dislocation density decreases linearly with mesa size, but extrapolates to a nonzero linear interface-dislocation density for a mesa size of zero. This nonzero extrapolation suggests an additional active source which generates a dislocation density that cannot be decreased to zero by decreasing the mesa size. Cathodoluminescence eeL) images using radiative recombination indicate that the additional source is nucleation from the mesa edges. Despite a doubling in epilayer thickness from 3500 to 7000 A, the linear interface-dislocation density for mesas 100 [tm in width is stm very low, approximately 1500 cm --l. The 8250"A layers possess interface-dislocation densities too high to be accurately determined with CL. However, increases in CL intensity as mesa width is reduced indicate that the interface-dislocation density is decreasing and that growth...

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Crystallinity and texturing of RF sputtered c-axis aligned crystal InGaZnO 4 (CAAC IGZO) thin films were quantified using X-ray diffraction techniques. Above 190 C, nanocrystalline films with an X-ray peak at 2h ¼ 30 (009 planes) developed with increasing c-axis normal texturing up to 310 C. Under optimal conditions (310 C, 10% O 2 ), films exhibited a c-axis texture full-width half-maximum of 20 . Cross-sectional high-resolution transmission electron microscopy confirmed these results, showing alignment variation of 69 over a 15 Â 15 nm field of view and indicating formation of much larger aligned domains than previously reported. At higher deposition temperatures, c-axis alignment was gradually lost as polycrystalline films developed. V C 2014 AIP Publishing LLC. [http://dx.

X 10-3) epilayers on GaAs was studied with scanning cathodoluminescence (CL), transmission electron microscopy (TEM), high-voltage electron microscopy, and scanning electron microscopy. CL shows that nonradiative recombination lines exist in the GaAs buffer layer as far as 4000 A from the interface. The density of these defects is independent of substrate dislocation density. Plan-view TEM analysis indicates that the majority of these dislocations in the buffer layer are sessile edge half-loops. Cross-sectional TEM shows that loops also extend into the InGaAs epilayer, but the majority ofthe loops are located on the buffer layer (substrate) side of the interface, A mode! is proposed to explain sessile edge dislocation formation in the buffer layer. A comparison of CL and high-voltage electron microscopy images from the same interface area reveals that the dark nonradiative recombination lines seen in scanning luminescence images in this high misfit system do not correspond to the normal, isolated misfit dislocation. The nonradiative recombination line spacing is 3 p.m, whereas the interface dislocation spacing is 400-1000 A. It is shown that the nonradiative recombination lines observed in CL of the interface correspond to specific groups of dislocations with different TEM contrast behavior. The dark nonradiative recombination lines also correlate with asymmetric surface ridges, suggesting that they introduce preferred nucleation sites, and that these effects are different for the two (110) directions.

The successful preparation of novel thin nanocomposite films containing continuous periodic arrays of self‐assembled silver nanocrystals in a polystyrene (PS) matrix is reported in this communication. The Figure shows a photo of a thin nanocomposite Ag–PS film supported by a wire loop. The simple and rapid synthetic procedure described here should be applicable to a variety of metal or semiconductor–polymer nanocomposite systems.

Structural and optical properties of strainrelaxed InAsP/InP heterostructures grown by metalorganic vapor phase epitaxy on InP(001) using tertiarybutylarsine We have investigated the strain relaxation of intentionally lattice mismatched (Ϯ0.5%͒ GaInP layers grown on GaAs substrates by organometallic vapor phase epitaxy. Double axis x-ray diffraction was used to measure the relaxation in these epitaxial layers in perpendicular ͗110͘ directions as a function of thickness. For samples in tension, the difference in relaxation between ͓110͔ and ͓110͔ increases from 10% to 48% as the layer thickness increases from 7 to 28 times the critical thickness, h c . For samples in compression this difference is 28% at 24h c while no relaxation is measured for a sample at 6h c . These results indicate that strain relaxes anisotropically and that the anisotropy is more pronounced for samples in tension than in compression. Furthermore, the major relaxation axis was found to be ͓110͔ regardless of the sign of the strain. Reciprocal space maps, generated using triple axis x-ray diffraction, showed that the amount of microtilt of the epitaxial layers was also anisotropic. This anisotropy and the direction of the maximum dislocation density which was measured by cathodoluminescence and transmission electron microscopy, changed from ͓110͔ in tension to ͓110͔ in compression. The fact that the major relaxation axis remained stationary while the high misfit dislocation density direction rotated indicates that a substantial number of dislocations with Burgers vectors of the ''wrong sense'' for strain relief are formed in compressed epilayers. A model in which ␣ type dislocations are more mobile than the ␤ type misfit dislocations regardless of the sign of the strain is consistent with all of the experimental observations.

Rectangular Schottky diodes were fabricated on In0.06Ga0.94As grown by organometallic vapor phase epitaxy on GaAs substrates patterned with mesas. The density of α and β misfit dislocations at the strained-layer interface changed with the size of the rectangular mesas. Since all mesas (four sizes and two orientations) are processed simultaneously, all other defect concentrations are expected to remain constant in each diode. Scanning cathodoluminescence showed that the misfit dislocation density varied linearly with rectangle size. Deep-level transient spectroscopy showed that an n-type majority-carrier trap is present at 0.58 eV below the conduction band with a concentration that increases with increasing α-type misfit dislocation density. The β misfit dislocation density had no influence the deep level spectra, indicating that this trap is related to the cores of only α-type misfit dislocations. The capture rate trend corroborates the view that the trap is associated with the dislocation cores and not with isolated defects. Calculations indicate that the trap concentration is comparable to the concentration expected if all of the dislocation core atoms are electrically active.