Hong Jun Bark

Rapid-thermal-annealing effect on lateral charge loss in metal–oxide–semiconductor capacitors with Ge nanocrystals

The rapid-thermal-annealing effect on lateral charge loss in metal–oxide–semiconductor capacitors with Ge nanocrystals is investigated by means of capacitance-voltage (C–V) and capacitance decay measurements. The C–V curves show the hysteresis indicating the charge storage effect in Ge nanocrystals. The hysteresis width shows strong annealing temperature dependence and shows the maximum at 700 °C meaning the maximum nanocrystal density. Capacitance decay experiment at flat-band voltage shows that the decay is dominated by two decay mechanisms. The initial fast discharge is more significant for samples annealed at lower temperatures. The cross-sectional transmission electron microscopic observations show the quasi-continuous Ge layer with Ge nanocrystals and Ge-rich amorphous regions for samples annealed at lower temperatures. Therefore, the fast discharging is attributed to lateral charge loss of insufficiently localized nanocrystals. On the other hand, the slow discharge is attributed to tunneling out of...

Ultralarge capacitance-voltage hysteresis and charge retention characteristics in metal oxide semiconductor structure containing nanocrystals deposited by ion-beam-assisted electron beam deposition

Amorphous silicon films are deposited by ion-beam-assisted electron beam deposition and subsequently oxidized by a rapid thermal oxidation process. The oxidized film contains a large density of nanocrystals specifically localized at a certain depth from the Si/SiOx interface, whereas no evidence of nanocrystals is found for oxidized films deposited without ion beam assistance. Such a marked contrast resulted from the enhancement of nucleation rate by ion beam irradiation. The metal-oxide-semiconductor structure utilizing the film shows an ultralarge capacitance–voltage hysteresis whose width is over 20 V. In addition capacitance–time measurement shows a characteristic capacitance transient indicating nondispersive carrier relaxation. The retention time shows a dependence on applied bias and the maximum time of ∼70 s is obtained near midgap voltage. The retention time dependence on applied bias and large capacitance–voltage hysteresis are attributed to direct tunneling of trapped charges in the deep traps ...

Charge retention characteristics in a metal–insulator–semiconductor capacitor containing Ge nanocrystals

We investigate the charge retention characteristics in a metal–insulator–semiconductor capacitor containing Ge nanocrystals (~3 nm in diameter) using capacitance–voltage measurements with various gate bias sweep rates. The metal–insulator–semiconductor capacitor is fabricated by pulsed laser deposition and rapid thermal oxidation. The capacitance–voltage curve shows the strong hysteresis indicating charging/discharging of carriers during the gate bias sweeping. The stored charge densities, evaluated from the flat band voltage shifts, show the non-dispersive carrier relaxation, which is a characteristic property for nanocrystals arranged in a layer. In addition, we observe an interesting capacitance ledge during forward bias sweeping. From the trap distribution determination by the Terman method, the capacitance ledge is due to an energetically localized trap at 0.33 eV + Ev. The energetic position of the trap is in agreement with the ground-state hole energy level in the Ge nanocrystals. This suggests the possibility that the trap level is related to the fact that the stored charges initially tunnel out at the ground-state hole energy level.

Formation of luminescent Si nanocrystals by high-temperature rapid thermal chemical vapor deposition

We observe a completely different growth regime of silicon-rich oxide (SRO) layers by rapid thermal chemical vapor deposition for the formation of luminescent nanocrystals. The growth regime is characterized by low [N2O]/[SiH4] ratios ( 700 °C). High-resolution cross-sectional transmission electron microscopy (XTEM) shows the bimodal distribution of large polycrystals and nanocrystals after post-deposition annealing. The luminescence is attributed to the nanocrystals. Fourier transform infrared spectroscopy in conjunction with XTEM and energy-dispersive x-ray studies show the phase separation and bonding reconfiguration in as-deposited SRO layers. The effectively increased oxygen content in the oxide matrix by phase separation and bonding reconfiguration reduces the diffusion coefficient of Si in the matrix, resulting in the formation of nanocrystals during post-deposition annealing.

Charge retention effect in metal–oxide–semiconductor structure containing Si nanocrystals prepared by ion-beam-assisted electron beam deposition

An amorphous Si layer prepared by ion-beam-assisted electron beam deposition (IBAED) method is oxidized by a rapid thermal oxidation technique. We observe a nanocrystal band located at about 4 nm from the Si/SiOx interface by cross-sectional transmission electron microscope observation. The metal–oxide–semiconductor (MOS) structure employing the oxide layer with the nanocrystal band exhibits a large capacitance–voltage hysteresis indicative of trapping of electrons/holes. In contrast, a relatively small capacitance–voltage hysteresis is found for the MOS diode prepared by conventional electron beam deposition (EBD) without ion-beam assistance. Such a marked difference shows that the ion-beam irradiation plays an important role in the formation of nuclei, which would grow to nanocrystals during subsequent rapid thermal oxidation process. Interestingly, the MOS prepared by IBAED shows a characteristic capacitance transient behavior, indicative of non-dispersive carrier relaxation. In addition, the charge retention times shows a bias dependence and a maximum of 72 s near the mid-gap voltage. Such a bias-dependent retention time is interpreted in terms of the tunneling of trapped charges in nanocrystals through empty interface states.

Area-selective formation of Si nanocrystals by assisted ion-beam irradiation during dual-ion-beam deposition

We investigate the effect of Ar-ion-beam irradiation during the deposition of SiOx films by dual-ion-beam deposition system. Ion-beam irradiation effectively increases the oxygen content, x, in SiOx films indicative of the preferential sputtering of Si phase as compared to SiO2 phase in SiOx films. We observe the intense photoluminescence from nonirradiated sample after postdeposition annealing at 1100°C indicating the formation of Si nanocrystals as shown by a cross-sectional transmission electron microscope. However, the increased oxygen content in ion-beam-irradiated sample results in small optical volume of small Si nanocrystals not sufficient for yielding appreciable photoluminescence intensity after postdeposition annealing. The property is utilized for achieving the area-selective formation of Si nanocrytals by inserting a shadow mask in assist ion beam during deposition.