Yeong-Dae Lim

Si-Compatible Cleaning Process for Graphene Using Low-Density Inductively Coupled Plasma

We report a novel cleaning technique for few-layer graphene (FLG) by using inductively coupled plasma (ICP) of Ar with an extremely low plasma density of 3.5 × 10(8) cm(-3). It is known that conventional capacitively coupled plasma (CCP) treatments destroy the planar symmetry of FLG, giving rise to the generation of defects. However, ICP treatment with extremely low plasma density is able to remove polymer resist residues from FLG within 3 min at a room temperature of 300 K while retaining the carbon sp(2)-bonding of FLG. It is found that the carrier mobility and charge neutrality point of FLG are restored to their pristine defect-free state after the ICP treatment. Considering the application of graphene to silicon-based electronic devices, such a cleaning method can replace thermal vacuum annealing, electrical current annealing, and wet-chemical treatment due to its advantages of being a low-temperature, large-area, high-throughput, and Si-compatible process.

Enhancement of light absorption using high-k dielectric in localized surface plasmon resonance for silicon-based thin film solar cells

The application of high-dielectric-constant (k) materials, e.g., Si3N4, ZrO2, and HfO2, to localized surface plasmon resonance (LSPR) excited by a Au nanoparticle structure has been investigated and simulated for the enhancement of light absorption in Si-based thin film solar cells by using Mie theory and three-dimensional finite-difference time-domain computational simulations. As compared to a conventional SiO2 dielectric spacing layer, the high-k dielectrics have significant advantages, such as (i) a polarizability over two times higher, (ii) an extinction cross-section 4.1 times larger, (iii) a 5.6% higher transmission coefficient, (iv) a maximal 39.9% and average 25.0% increase in the transmission of the electromagnetic field, (v) an absorption of the transmitted electromagnetic field that is a maximum of 2.8 times and an average of 1.4 times greater, and (vi) increased absorption efficiency and extended cover range. Experimental results show that the average absorptance in the visible spectrum using...

SELF-ASSEMBLY OF Si NANOSTRUCTURES IN SF6/O2 PLASMA

Self-assembled Si nanostructure arrays were formed in an inductively coupled plasma (ICP) reactor using SF6/O2 plasma at noncryogenic temperature. It was possible to form nanopillar arrays of a mean diameter of ~100 nm and a mean height up to 4.77 μm over areas >100 cm2. The self-assembly of the nanostructures was studied as a function of time, bias RF-power, and O2/SF6 ratio. It was found that the nanostructure arrays could be formed only when O2/SF6 was in the range of 0.8 to 2.5. Two types of the self-assembled nanostructure arrays were formed at the different bias RF-power ranges: one was nanohole arrays and the other was nanopillar arrays. The hole-type nanostructure was formed when the bias power was low at ~10 W, while the pillar-type nanostructure was formed when the bias power increased to 30 W. It was also found that, the height of the nanostructure arrays increased with the onset of an etching time of 40 s, but it decreased after excessively long etching time as the nanostructure arrays could no longer sustain themselves. The correlation between the formation of nanostructures and plasma properties was investigated using OES, XPS, AFM, and SEM analyses. According to the analyses, sidewall passivation layers which were formed by the reaction of Si with F and O radicals generated from the SF6/O2 plasma were responsible for giving rise to various nanostructure arrays.

High efficiency radial-junction Si nanohole solar cells formed by self-assembling high aspect ratio plasma etching

A drastic improvement in conversion efficiency was achieved from Si solar cells with radial-junction nanohole structure of a high aspect ratio of ∼10 which is fabricated by self-assembling plasma etching. A conversion efficiency of 27.8 % was predicted based on an optimization of various structural parameters by numerical simulations, and a design principle for realizing high efficiency Si nanohole surface texture for photovoltaic devices was demonstrated.