Liuhong Ma

Blue-violet photoluminescence from amorphous Si-in-SiNx thin films with external quantum efficiency in percentages

Bright blue-violet photoluminescence centered at 428nm was obtained in amorphous Si-in-SiNx thin films prepared in a cyclic growth mode on cool substrates by plasma-enhanced chemical vapor deposition, in which the typical size of the silicon particles has been brought down to ∼1.80nm and the number density amounts to 1.07×1013cm2. A maximum external quantum efficiency over 3.0% was measured in the as-deposited samples. Time-resolved photoluminescence spectra revealed decay times within nanosecond even at room temperature, disclosing a fast recombination dynamics in this amorphous system. The excellent efficiency can be attributed to a better passivation of the silicon particles—hence, the conventional rapid thermal annealing has a negligible effect on the photoluminescence intensity—and also to an improved transparency of the film by cyclic growth. The high-efficiency, tunable wavelength and nanosecond decay time at room temperature, achieved via a low-temperature process without invoking any posttreatmen...

Low-temperature electron mobility in heavily n-doped junctionless nanowire transistor

The electron mobility in a heavily n-doped junctionless nanowire transistor is demonstrated by the experimental investigation of the transfer characteristics at low temperatures. It is found that the minimum electron mobility at a critical low temperature results from the interplay of the thermal activation and impurity scattering. The temperature-dependence tendency of the normalized electron mobility by theoretical calculation and experimental extraction reveals that the thermal activation is responsible for the impact of the donor ionization and thermal energy on the electron mobility.

Low temperature growth of amorphous Si nanoparticles in oxide matrix for efficient visible photoluminescence

We report a low temperature procedure for the fabrication of highly luminescent silicon nanoparticles in silicon-rich oxide films. A number density over 1012∕cm2 has been achieved for silicon particles of about 3nm in size by plasma-enhanced chemical vapor deposition at a substrate temperature of 30°C. Such deposits, when post-annealed at 500°C for 2 min, manifested a photoluminescence two orders of magnitude more intense than those samples grown at 250°C. Strong photoluminescence in the whole visible light range has been measured in samples prepared with this low-temperature procedure. The present results indicate the feasibility of fabricating silicon-based light-emitting devices with moderate processing temperatures.

Effect of oxygen inclusion on microstructure and thermal stability of copper nitride thin films

Copper oxynitride thin films with a minor oxygen content were prepared on silicon wafers at 100 °C by reactive magnetron sputtering using a gas mixture of nitrogen and oxygen. Addition of oxygen immediately improves the compactness of the deposits, which otherwise comprise ragged Cu 3 N nanocrystallites. With an oxygen content <10.0 at.%, the deposits reveal some sporadic Cu 2 O nanocrystals under transmission electron microscopy, but their x-ray diffraction (XRD) patterns exhibit reflections only from the Cu 3 N phase. The decomposition temperature, at which the sample after prolonged annealing shows Cu reflections on its XRD pattern, can be raised from 300 °C for stoichiometric Cu3N to 360 °C. The decomposition product after annealing at 450 °C is pure copper having an electrical resistivity of 8.94 × 10 �8 ·m at room temperature, which can be taken as a good conductor and stands in strong contrast with the oxynitride matrix with an electrical resistivity of 6.87 × 10 �2 ·m. These results constitute progress in the search of directly writable copper nitride-based materials.

Temperature dependence of electronic behaviors in n-type multiple-channel junctionless transistors

The electronic behaviors in the n-type multiple-channel junctionless nanowire transistors are investigated in the thermal range from 10 K to 300 K. At low temperatures (T < 100 K), oscillation current spikes are clearly observed below flatband voltage and attributed to resonant tunneling through donor-induced quantum dot array. There is a minimum value at the critical temperature of 15 K for the drain currents and the electron mobility. The electron mobility increases rapidly above 15 K because of the thermal activation of ionized electrons. The temperature-dependent background trapping at the interface of silicon and silicon dioxide is evaluated by an Arrhenius-type off-state current with the activation energy of approximately 49 meV. As temperatures increasing, the negative shift of the threshold voltage with the slope of 4.0 mV K−1 is given predominantly by the thermal activation of traps.

Growth of nearly one nanometer large silicon particles in silicon carbide and their quantum-confined photoluminescence features

Silicon particles approaching the size of 1 nm were grown along with the confining SiC films by employing a low-temperature chemical vapor deposition procedure. The resulting amorphous composite structure enables an experimental study of the quantum confinement effect in extremely narrow potential wells, as exemplified here by photoluminescence measurement. Owing to the enhanced energy fluctuation for such small particles, strong photoluminescence centered at 450–540 nm, and of comparable profiles, was measured in one single sample with an excitation wavelength selectable within 360–420 nm. Moreover, the typical decay time was found to be below 3.0 ns. These properties hold promise for the fabrication of wide-spectrum photoreceptors, ultraviolet-light detectors, and other optoelectronic devices.

Nanoindentation and photoreflectance study on polycrystalline ternary Al–C–N thin films

Berkovich hardness and optical gap were determined by nanoindentation and photoreflectance measurement for ternary Al–C–N thin films of various compositions along with structural characterization. The deposits were fabricated by reactive magnetron sputtering of aluminum target onto Si(100) substrates, with the mixture of argon, nitrogen, and methane as precursor. High-resolution transmission electron microscopy and selected-area electron diffraction revealed a polycrystalline structure with rich defects in the film, and x-ray diffraction displays only one reflection at 2θ≈36° from the basal planes. The hardness is over 26GPa for all the deposits, it measures 53.4GPa in the sample Al47C20N33. The optical gap, defined as the photon energy where (1∕R)(dR∕dE) maximizes, R is the photoreflectance, lies within 5.2to5.6eV. These results indicate the wide-gap nature of aluminum carbonitrides, implying diverse potential applications of their thin films as protective coating of an ultraviolet detector, dielectric b...

Electron transport behaviors through donor-induced quantum dot array in heavily n-doped junctionless nanowire transistors

We investigated single electron tunneling through a phosphorus donor-induced quantum dot array in heavily n-doped junctionless nanowire transistor. Seven subpeaks splitting in current oscillations are clearly observed due to the coupling of quantum dot array under the bias voltage below 1.0 mV at the temperature of 6 K. The conduction system can be well described by a two-band Hubbard model. The activation energy of phosphorus donors is tuned by the gate voltage to be 7.0 meV for the lower Hubbard band and 4.4 meV for the upper Hubbard band due to the localization effects below threshold voltage. The evolution of electron behaviors in the quantum dots is identified by adjusting the gate voltage from quantum-dot regime to one-dimensional regime.

Observation of Degenerate One-Dimensional Subbands in Single n-Channel Junctionless Nanowire Transistors

We experimentally investigate one-dimensional electron transport in single n-channel junctionless nanowire transistor at low temperature. Current step increases with the gate voltage is clearly observed at the temperature of 6 K, attributed to the electron transport through one-dimensional subbands formed in the nanowire. The height of the first and the fourth steps is half of that of the second and the third steps, resulting from the twofold degeneracy of certain subbands.

Electric-field-dependent charge delocalization from dopant atoms in silicon junctionless nanowire transistor*

We study electric-field-dependent charge delocalization from dopant atoms in a silicon junctionless nanowire transistor by low-temperature electron transport measurement. The Arrhenius plot of the temperature-dependent conductance demonstrates the transport behaviors of variable-range hopping (below 30 K) and nearest-neighbor hopping (above 30 K). The activation energy for the charge delocalization gradually decreases due to the confinement potential of the conduction channel decreasing from the threshold voltage to the flatband voltage. With the increase of the source–drain bias, the activation energy increases in a temperature range from 30 K to 100 K at a fixed gate voltage, but decreases above the temperature of 100 K.