Jia-Min Shieh

Near-infrared femtosecond laser-induced crystallization of amorphous silicon

Amorphous silicon (a-Si) was crystallized by femtosecond laser annealing (FLA) using a near-infrared (λ≈800nm) ultrafast Ti:sapphire laser system. The intense ultrashort laser pulses lead to efficient nonlinear photoenergy absorption and the generation of very dense photoexcited plasma in irradiated materials, enabling nonlinear melting on transparent silicon materials. We studied the structural characteristics of recrystallized films and found that FLA assisted by spatial scanning of laser strip spot constitutes superlateral epitaxy that can crystallize a-Si films with largest grains of ∼800nm, requiring laser fluence as low as ∼45mJ∕cm2, and low laser shots. Moreover, the optimal annealing conditions are observed with a significant laser-fluence window (∼30%).

Enhanced photoresponse of a metal-oxide-semiconductor photodetector with silicon nanocrystals embedded in the oxide layer

The authors report a two-terminal metal-oxide-semiconductor photodetector for which light is absorbed in a capping layer of silicon nanocrystals embedded in a mesoporous silica matrix on p-type silicon substrates. Operated at reverse bias, enhanced photoresponse from 300to700nm was observed. The highest optoelectronic conversion efficiency is as high as 200%. The enhancements were explained by a transistorlike mechanism, in which the inversion layer acts as the emitter and trapped positive charges in the mesoporous dielectric layer assist carrier injection from the inversion layer to the contact, such that the primary photocurrent could be amplified.

The Effect of Plating Current Densities on Self-Annealing Behaviors of Electroplated Copper Films

In this study, the effect of plating current densities on self-annealing behaviors of electroplated Cu films was found to be relevant to the polarization resistance of electroplating systems. Porous films with defects occurred at low plating current density or at low polarization resistance. In contrast, dense films with small grains occurred at higher plating current density or at higher polarization resistance. However, when more current was further supplied, Cu aggregation occurred and deposited films became spongy or dendritic. We suggest that both the defects within porous films and the underlying energy of fine-grained deposits accelerated self-annealing. These two characteristics competed with each other to determine the resistivity drop by self-annealing. On the other hand, the (111) texture evolutions of deposited Cu films with an increase of plating current densities were consistent with the evolutions of resistivity and surface morphology.

Low-temperature growth of ZnO nanorods in anodic aluminum oxide on Si substrate by atomic layer deposition

Low-temperature growth of self-organized ZnO nanorods on Si substrate is achieved using anodic aluminum oxide and atomic layer deposition at 250°C without catalyst or seed layer. Photoluminescence spectrum indicates that the ZnO nanorod arrays exhibit a blue∕green luminescence at 480nm. In addition, the nanorod arrays demonstrate excellent field-emission properties with a turn-on electric field of 6.5Vμm−1 and a threshold electric field of 9.8Vμm−1, which are attributed to the perfectly perpendicular alignment of ZnO nanorods to the Si substrate.

Roll-to-roll fabrication of large scale and regular arrays of three-dimensional nanospikes for high efficiency and flexible photovoltaics

Three-dimensional (3-D) nanostructures have demonstrated enticing potency to boost performance of photovoltaic devices primarily owning to the improved photon capturing capability. Nevertheless, cost-effective and scalable fabrication of regular 3-D nanostructures with decent robustness and flexibility still remains as a challenging task. Meanwhile, establishing rational design guidelines for 3-D nanostructured solar cells with the balanced electrical and optical performance are of paramount importance and in urgent need. Herein, regular arrays of 3-D nanospikes (NSPs) were fabricated on flexible aluminum foil with a roll-to-roll compatible process. The NSPs have precisely controlled geometry and periodicity which allow systematic investigation on geometry dependent optical and electrical performance of the devices with experiments and modeling. Intriguingly, it has been discovered that the efficiency of an amorphous-Si (a-Si) photovoltaic device fabricated on NSPs can be improved by 43%, as compared to its planar counterpart, in an optimal case. Furthermore, large scale flexible NSP solar cell devices have been fabricated and demonstrated. These results not only have shed light on the design rules of high performance nanostructured solar cells, but also demonstrated a highly practical process to fabricate efficient solar panels with 3-D nanostructures, thus may have immediate impact on thin film photovoltaic industry.

Frequency-Dependent Complex Conductivities and Dielectric Responses of Indium Tin Oxide Thin Films From the Visible to the Far-Infrared

Transparent and conducting indium tin oxide (ITO) thin films form an integral part for various optoelectronic devices. In this paper, we report the frequency-dependent complex conductivities and dielectric responses of several sputtered ITO thin films with thicknesses in the range of 189-962 nm by using terahertz time domain spectroscopy (THz-TDS), optical reflectance spectroscopy, and electrical measurements. The plasma frequencies are verified to be from 1590 to 1930 rad·THz, while the scattering times are in the range 6-7 fs based on the Drude free-electron model. The mobilities of the above ITO thin films are calculated to be 32.7-34.2 cm2 V-1 s-1, whereas the carrier concentrations lie in the range 2.79-4.10× 1020 cm-3. The electrical properties derived from the THz-TDS technique agree well with those determined by Hall measurement. Parameters for the complex dielectric function suitable for ITO in the range 0.2-2 and 4-450 THz are also determined.

Investigations of effects of bias polarization and chemical parameters on morphology and filling capability of 130 nm damascene electroplated copper

Through elucidating the effects of current density, cupric ion concentration, bath temperature, and air agitation on plating uniformity and filling capability of copper electroplating, the deposition of copper in an acid copper electrolyte will be illustrated to scale down to the sub-0.13 μm features with uniform plating, which is required by chemical mechanical polishing in current damascene techniques. In order to achieve the defect-free filling in sub-0.13 μm vias and trenches, the electrolyte must be composed of proper amounts of cupric ions, sulfuric acid, chloride ions, wetting agent, and filling promoter. The supplied current controlled at a lower current density, agitation acceded to the electroplating process were found as further keys. In the electrolyte, the filling promoter was consisted essentially of thiazole derivatives with benzyl groups and amino-group (−NH2) offering sufficient inhibition on copper depositing and selective inhibition gradient. Moreover, a lower resistivity film and highe...

Characterization of additive systems for damascene Cu electroplating by the superfilling profile monitor

Gap-filling dynamics of several different species of additives for copper electrodeposition was investigated by monitoring the cross section of a partially filled copper profile on the scanning electron microscopy photo. The filling ration Δy/Δx between “bottom-up” with “sidewall shift” was found to be proportional to the filling power of additives. The adsorption-diffusion model combined with cathode polarization and cyclic voltammetric stripping measurements was employed to explain the attribution of additives in superfilling phenomena. The superfilling dynamics was achieved under behavior of additives providing selective inhibition gradient within the damascene feature. By means of those analyses, we have optimized the appropriate amount of additives and achieved the superfilling performance for 0.15 μm vias with aspect ratio 6 by an acid-copper electrolyte with polyethylene glycol, C1−, and 2-mercaptopyridine (2-MP). Due to the additive of 2-MP, chelate formed which enhanced adsorption ability on Cu0 ...

Fast Programming Metal-Gate Si Quantum Dot Nonvolatile Memory Using Green Nanosecond Laser Spike Annealing

The ultrafast metal-gate silicon quantum-dot (Si-QD) nonvolatile memory (NVM) with program/erase speed of 1 μs under low operating voltages of ± 7 V is achieved by thin tunneling oxide, in situ Si-QD-embedded dielectrics, and metal gate. Selective source/drain activation by green nanosecond laser spike annealing, due to metal-gate as light-blocking layer, responds to low thermal damage on gate structures and, therefore, suppresses re-crystallization/deformation/diffusion of embedded Si-QDs. Accordingly, it greatly sustains efficient charge trapping/de-trapping in numerous deep charge-trapping sites in discrete Si-QDs. Such a gate nanostructure also ensures excellent endurance and retention in the microsecond-operation Si-QD NVM.

Near-infrared silicon quantum dots metal-oxide-semiconductor field-effect transistor photodetector

A fully silicon-based metal-oxide-semiconductor field-effect transistor is demonstrated for the detection of near-infrared light. Si nanocrystals (nc-Si) are synthesized in the nanopore channels of mesoporous silica (MS) inserted between two oxide layers to form a complete gate structure of polycrystalline Si/SiO2/nc-Si-in-MS/SiO2 with a polycrystalline Si electrode. Illuminating the gate with near-infrared light, a photoresponsivity as high as 2.8 A/W at 1.55 μm can be achieved. The improved photoresponsivity is attributed to from optical transitions via interface states and a current amplification mechanism of the device.