J. I. Dijkhuis

Ultrafast screening and carrier dynamics in ZnO: Theory and experiment

At carrier densities above the Mott density, Coulomb screening destroys the exciton resonance. This, together with band-gap renormalization and band filling, severely affects the optical spectra. We have experimentally studied these effects by ultrafast pump-probe reflectivity measurements on a ZnO single crystal at various wavelengths around the exciton resonance and in a broad carrier-density range. Theoretically, we determined the Mott density in ZnO to be

Subpicosecond shifting of the photonic band gap in a three-dimensional photonic crystal

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Coherent vibrations of submicron spherical gold shells in a photonic crystal

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Random telegraph signals and 1/f noise in a silicon quantum dot

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SINGLE ELECTRON TUNNELING AND SUPPRESSION OF SHORT-CHANNEL EFFECTS IN SUBMICRON SILICON TRANSISTORS

at 300 K. Taking a field-theoretical approach, we derived and solved the Bethe-Salpeter ladder equation and we computed the density-dependent reflectivity and absorption spectra. A carrier dynamics model has been developed, containing three-photon absorption, carrier cooling, and carrier trapping near the surface. The agreement between the theoretical reflectivity based on our model and the experimental data is excellent.

Ultrafast all-optical shutter based on two-photon absorption

We demonstrate spectral shifting of the photonic band gap in a three-dimensional photonic crystal within a time of less than 350fs. Single 120fs high-power optical pulses are capable to induce the transition from the semiconductor to the metallic phase of VO2 in the pores of our artificial silica opal. The phase transition produces a substantial decrease of the real part of the effective refractive index of the photonic crystal and shifts the spectral position of the photonic band gap.

Optical generation and detection of shock waves in sapphire at room temperature

Coherent acoustic radial oscillations of thin spherical gold shells of submicron diameter excited by an ultrashort optical pulse are observed in the form of pronounced modulations of the transient reflectivity on a subnanosecond time scale. Strong acousto-optical coupling in a photonic crystal enhances the modulation of the transient reflectivity by up to 4%. The frequency of these oscillations is demonstrated to be in good agreement with the Lamb theory of free gold shells.

Saturation effects in femtosecond laser ablation of silicon-on-insulator

We investigated random telegraph signals and 1/f noise in a submicron metal–oxide–semiconductor field-effect transistor at low temperatures in the Coulomb-blockade regime. The rich noise characteristics were studied as a function of gate voltage, drain current, and temperature, both in and beyond the Ohmic regime. The results can be understood within a simple model assuming a uniform potential fluctuation of constant magnitude at the location of the dot. Clear signatures of electron heating are found from the noise at higher currents.

Localization of the Si–H stretch vibration in amorphous silicon

We report measurements on submicron metal–oxide–semiconductor field effect transistors equipped with a gate on three sides of the channel. At room temperature, a strong suppression of short-channel effects has been achieved for the narrowest channels. At liquid helium temperatures, the same devices exhibit clear conductance oscillations in the subthreshold regime, indicating that a quantum dot has formed in the disordered channel.

Low-frequency noise in quantum point contacts

An ultrafast all-optical shutter is presented, based on a simple two-color, two-photon absorption technique. For time-resolved luminescence measurements, this shutter is an interesting alternative to the optical Kerr gate. The rejection efficiency is 99%; the switching-off and switching-on speeds are limited by the pulse length only; the rejection time is determined by the crystal slab thickness; and the bandwidth spans the entire visible spectrum. We show that our shutter can also be used for accurate measurement of group velocity inside a transparent material.