Search

Tungsten suboxide (WOx) nanorods that are directly grown on electrochemically etched tungsten (W) tips are used as probes of a double-scanning-probe tunneling microscope. A WOx nanorod well acts as a scanning probe in tunneling microscopy and stable atomic-scale imaging is confirmed. For a contact nanoelectrode in measuring electrical properties of nanostructures, the WOx nanorod probe is coated with platinum. A series of resistance measurements of an erbium-disilicide nanowire as a function of interprobe distance down to 72 nm is realized. [ABSTRACT FROM AUTHOR]

We have measured the electric properties of nanosized Schottky contacts formed between ErSi2 nanowires (NWs) and a Si(001) substrate. Current vs voltage (I-V) measurement was performed by touching a scanning tunneling microscope tip to the NWs. The current density (J) through the ErSi2/Si(001) interface increased as the width of the NWs decreased, while no significant changes were observed upon changing the length of the NWs. The ideality factor was estimated by fitting the standard Schottky equation to the obtained J-V curves. Our results suggest that the tunneling component increases as the width of the NWs becomes smaller. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) decay time measurements at 77 and 300 K are reported from 6.1 nm GaAs single quantum well heterostructures (SQWH’s) confined by GaAs/AlAs short-period superlattices (SPS’s) or ternary AlGaAs alloys with similar Al content, prepared by molecular beam epitaxy. The SQW PL intensity exhibits a single exponential decay with a time constant of 1.6 ns for SQWH’s confined by SPS’s and 0.3 ns for SQWH’s confined by AlGaAs alloys at 77 K. From comparison of the decay rates in both types of the sample, it is found that the radiative recombination efficiency is improved by a factor of about 6 in SPS confined SQWH’s. This higher efficiency is attributed to the improved heterointerfaces in addition to the enhanced radiative recombination rate due to the increased overlap of electron and hole wave functions in the narrow SQW. [ABSTRACT FROM AUTHOR]

Ridge waveguide AlGaAs/GaAs distributed feedback lasers with multiple quantum well structure were fabricated for the first time. The threshold current of 28 mA, which is the lowest ever reported among AlGaAs/GaAs distributed feedback lasers, was obtained at room temperature. Stable single longitudinal and transverse mode oscillation was observed over the wide temperature range. The dynamic linewidth was also measured and it was five to six times smaller than that of a double heterostructure distributed feedback laser. [ABSTRACT FROM AUTHOR]

Effects of substrate preparation conditions, i.e., wet chemical and ultrahigh vacuum cleaning preparations, on GaAs oval defects grown by molecular beam epitaxy (MBE) were investigated. It is found that, with our MBE system, the presence of the smaller (<10 μm) ovally shaped defects without macroscopic core particulates can be ascribed to surface microscopic contaminations. Most of the other remaining larger (>10 μm) oval defects with core particulates observed on 1-μm-thick GaAs MBE layers are attributed to surface macroscopic contaminations. The total density is reduced to 300 cm-2 without significantly modifying the growth cell parameters. [ABSTRACT FROM AUTHOR]

A very stable amorphous SiC/Si (a-SiC/a-Si) heterojunction solar cell has been developed. The cell structure is of multijunction type with blocking barriers for the dopants and metal diffusion. This new tandem cell exhibits excellent stability for both thermal and sunlight conditions. After 2000 h of light exposure, an observable photodegradation is not seen in the cell performance. The improvements are achieved by the low-temperature deposition of first a p a-SiC layer, and by the blocking barriers for dopants and metal diffusion. [ABSTRACT FROM AUTHOR]

Observation of free excitons is reported in room-temperature photoluminescence of nominally undoped GaAs/AlGaAs single quantum wells grown by molecular beam epitaxy. A comparative study with parallel-conduction photocurrent spectroscopy shows that a sharp luminescence peak with a linewidth of 14 meV observed for the 6.1-nm-wide well coincides within 2 meV with the n=1 heavy-hole free-exciton resonance line at excess carrier densities less than 1017 cm-3. Excitonic decay channels dominate the luminescence spectrum even at room temperature as a result of quantum confinement effects, although photogenerated carriers are also provided for photocurrents by exciton dissociations. [ABSTRACT FROM AUTHOR]

By investigating the linear polarization dependence of intrinsic emissions from undoped GaAs/AlAs short-period superlattices at room temperature, it is shown that a dominating peak observed in the normal emission spectra is due to the free-carrier recombination associated with the lowest electron to mixed-hole subbands with an unexpectedly large light-hole character instead of with the lowest electron to pure heavy-hole subbands expected in an ideal superlattice. Origins of the extensive valence-band mixing in the synthesized superlattices are discussed in relation to microscopic fluctuations in the layer thicknesses observed in the transmission electron microscope lattice image. [ABSTRACT FROM AUTHOR]

The trapping efficiency and trapping dynamics of photoexcited carriers in GaAs/AlGaAs single quantum wells with different confinement structures are examined at low temperature by means of picosecond luminescence as well as photoluminescence excitation spectroscopy. The trapping efficiency is 100% only in graded-index separate confinement heterostructures with a linear band-gap profile. The lower trapping efficiency of other confinement structures is due to radiative and nonradiative recombination in the confinement layers. [ABSTRACT FROM AUTHOR]

GaAs/AlGaAs transverse junction stripe lasers with a distributed feedback structure were fabricated. The cw threshold current was 27 mA at 20 °C. The laser operated in a pure single longitudinal mode at the wavelength of 867 nm. [ABSTRACT FROM AUTHOR]