Jung-Sung Kim

Formation and electrical properties of Ni1−xFex nanocrystals embedded in a polyimide layers for applications as nonvolatile flash memories

Self-assembled Ni1−xFex nanoparticles embedded in a polyimide (PI) matrix were formed by curing Ni1−xFex thin films with PI precursor layers. Transmission electron microscopy images and selected area electron-diffraction patterns showed that Ni1−xFex nanocrystals were created inside the PI layer. Capacitance-voltage measurements on Al/PI/nanocrystalline Ni1−xFex∕PI∕n-Si structures at 300K showed a metal-insulator-semiconductor behavior with a large flatband voltage shift due to the quantum confinement effect of the Ni1−xFex nanocrystals in spite of the possible existence of a thick tunnel PI layer, and conductance-voltage measurements showed a broad conductance peak around the flatband voltage. The present results suggest that self-assembled Ni1−xFex nanocrystals embedded in a PI layer hold promise for potential applications in nonvolatile flash memories with floating gates consisting of Ni1−xFex nanocrystals embedded in a PI layer.

Three-dimensional electronic properties of multiple vertically stacked InAs∕GaAs self-assembled quantum dots

The microstructural properties and the shape of an InAs∕GaAs array grown by molecular beam epitaxy were studied using transmission electron microscopy (TEM) measurements, and the interband transitions were investigated by using temperature-dependent photoluminescence (PL) measurements. The shape of the InAs quantum dots (QDs) on the basis of the cross-sectional bright-field TEM image was modeled to be a convex-plane lens. The electronic subband energies and the wave functions were numerically calculated by using a three-dimensional finite-difference method, taking into account strain effects. The excitonic peaks corresponding to interband transitions from the ground electronic subband to the ground heavy-hole band (E1-HH1) in the multiple-stacked QDs, as determined from the PL spectra, were in reasonable agreement with the (E1-HH1) interband transition energies obtained from the results of the numerical calculations.

Efficient formation of surface relief grating on azopolymer films by gold nanoparticles

This paper reports a method for the efficient formation of surface relief grating (SRG) on azopolymer films in which gold nanoparticles are dispersed. The height and shape of the SRG, which were formed by a two-beam interference technique, were found to be dependent on the content of gold nanoparticles. The optimum concentration of gold nanoparticles for the efficient formation of SRG was confirmed by atomic force microscopy (AFM), and the height of SRG at the content of 0.06 wt % was about 2.2 times higher than that of pure azopolymer film without gold nanoparticles. This is due to the field enhancement effect derived from the localized plasmon excitations of gold nanoparticles dispersed in the azopolymer film.

Effects of two-dimensional electron gas on the optical properties of InAs/GaAs quantum dots in modulation-doped heterostructures

The Shubnikov–de Haas data showed that the carrier density of two-dimensional electron gas (2DEG) in the GaAs active region containing InAs quantum dot (QD) arrays embedded between modulation-doped Al0.25Ga0.75As/GaAs heterostructures increased with increasing doping concentration in the modulation layer. The transmission electron microscopy images showed that the sizes of the self-assembled InAs vertically stacked QD arrays inserted in the GaAs did not change significantly with increasing carrier density of the 2DEG. The photoluminescence (PL) spectra showed that the peaks corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole subband of the InAs QDs shifted to the higher energy side with increasing density of the 2DEG and that the full width at half maximum of the PL spectrum increased slightly with increasing density of the 2DEG.

Surface relief grating formation on an azo-polymer

Two types of photo-induced gratings, birefringence and surface relief gratings, were formed on an azo polymer film when two orthogonal circularly polarized writing beams irradiated the film. All the diffracted beams from the gratings were measured during irradiation and the surface relief height inscribed on the film was measured by using atomic force microscope (AFM) after the irradiation. The transmitted beam intensities were calculated using a Jones matrix for two gratings. The phase differences for the two gratings were separately determined by fitting the experimental results to the theory. Next, the changes of the phase differences of two gratings were measured in-situ using an exact equations. The results from this method agreed with previous one. The phase difference between two gratings was measured. The phase difference between two gratings converged on about 45 degrees in our case. Diffraction efficiency measurement and analysis revealed that the two gratings were independent of each other and that the mechanisms for the two gratings were different.