Soyoung Kwon

Investigation of electrical properties and stability of Schottky contacts on (NH4)2Sx‐treated n‐ and p‐type In0.5Ga0.5P

A study on the interface properties of Schottky contacts on  (NH4)2Sx‐treated n‐ and p‐type In0.5Ga0.5P is carried out. The effects of sulfur (S) treatment on Schottky barrier height are investigated by employing capacitance‐voltage and current‐voltage (I‐V) measurements. It is also demonstrated that the passivation effects of S treatments on the interface traps can be monitored by deep level transient spectroscopy (DLTS) measurements. It is observed that the S treatment increases the dependence of Schottky barrier height on the metal work function. The interface traps in the Schottky contact formed by the heat treatment are found to give their energy state above midgap. It is found that the S treatment can passivate these interface traps as well as suppress their generation under the heat treatment. For both n‐ and p‐In0.5Ga0.5P, contact‐related majority carrier traps, which are different from the thermally generated interface traps, are observed at the Al‐In0.5Ga0.5P interface and they can be annealed o...

Interface properties of (NH4)2Sx‐treated In0.5Ga0.5P Schottky contacts

The effects of (NH4)2Sx solution treatment on the interface properties of metal‐In0.5Ga0.5P Schottky contacts have been investigated by capacitance‐voltage measurements and deep‐level transient spectroscopy measurements. The (NH4)2Sx‐treated samples show Schottky barrier heights that are more sensitive to the metal work functions. It is also found that (NH4)2Sx treatment of In0.5Ga0.5P can passivate the phosphorus‐vacancy‐related interface deep traps of Schottky contacts as well as suppress the generation of interface deep traps due to heat treatment.

The effect of CO2 in free-radical polymerization of 2,2,2-trifluoroethyl methacrylate

Carbon dioxide is an effective diluent for increasing the free volume of polymer. It has useful advantages with reductions of viscosity, surface tension and with an increase of diffusion into polymer. These properties are available in polymer processing and particle designing. We carried out free-radical polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) with AIBN as the initiator in carbon dioxide. This experiment was performed at fixed temperature (343 K), stirring speed and weight of monomer+initiator. Only weight ratios of carbon dioxide were changed. Molecular weight and Tg showed a minimum at 14.1 MPa and increased in the higher final pressure.

Energy dissipation of nanoconfined hydration layer: Long-range hydration on the hydrophilic solid surface

The hydration water layer (HWL), a ubiquitous form of water on the hydrophilic surfaces, exhibits anomalous characteristics different from bulk water and plays an important role in interfacial interactions. Despite extensive studies on the mechanical properties of HWL, one still lacks holistic understanding of its energy dissipation, which is critical to characterization of viscoelastic materials as well as identification of nanoscale dissipation processes. Here we address energy dissipation of nanoconfined HWL between two atomically flat hydrophilic solid surfaces (area of ~120 nm2) by small amplitude-modulation, noncontact atomic force microscopy. Based on the viscoelastic hydration-force model, the average dissipation energy is ~1 eV at the tapping amplitude (~0.1 nm) of the tip. In particular, we determine the accurate HWL thickness of ~6 layers of water molecules, as similarly observed on biological surfaces. Such a long-range interaction of HWL should be considered in the nanoscale phenomena such as friction, collision and self-assembly.

Characteristics of electron traps in In0.5Ga0.5P generated by recombination enhanced defect reactions

We report the observation of a new type of intrinsic defect in n‐In0.5Ga0.5P which can be generated by recombination enhanced defect reaction (REDR) mechanism. It is observed that the increases of the concentrations of this defect and of another native defect due to REDR have nearly linear time dependence before saturation. This observation and other experimental results suggest that the two observed defects are complex defects. Other electrical properties of these defects such as alloy broadening effect on the thermal ionization energy are also described.

Effect of oxygen on the electrical and optical properties of In0.5Ga0.5P grown by liquid‐phase epitaxy

The effect of oxygen on the electrical and optical properties of In0.5Ga0.5P epitaxial layers grown on (100) GaAs by liquid‐phase epitaxy has been investigated by adding Ga2O3 to the growth melt. As the amount of Ga2O3 increases, the carrier concentration at 300 K decreases from 4×1016 to 4×1015 cm−3 and the Hall mobility at 77 K increases from 2400 to 4000 cm2/V s. The photoluminescence at 17 K shows that the peak intensity of an extrinsic transition in the In0.5Ga0.5P layer is reduced when Ga2O3 is added to the growth melt. These facts indicate that the main effect of Ga2O3 is the reduction of impurity concentration in the growth melt. In the In0.5Ga0.5P layer grown from the Ga2O3‐added growth melt, the same deep trap, with an activation energy of 0.29 eV, as in an undoped layer is observed but the trap density is decreased. This implies that the deep trap is not due to a simple intrinsic defect, but related to an impurity.

Chemical trends of S‐, Se‐, and Te‐related DX centers in InGaP

Deep level properties of S‐, Se‐, and Te‐doped In1−xGaxP layers grown by liquid phase epitaxy are studied by deep level transient spectroscopy and capacitance‐temperature measurements. From the dependence of deep level properties on the impurity species and also from the existence of persistent photoconductivity, these impurity‐related deep levels are attributed to the DX centers. The emission activation energies of these centers are observed to decrease as their atomic number increases.

Quartz tuning fork-based frequency modulation atomic force spectroscopy and microscopy with all digital phase-locked loop

We present a platform for the quartz tuning fork (QTF)-based, frequency modulation atomic force microscopy (FM-AFM) system for quantitative study of the mechanical or topographical properties of nanoscale materials, such as the nano-sized water bridge formed between the quartz tip (~100 nm curvature) and the mica substrate. A thermally stable, all digital phase-locked loop is used to detect the small frequency shift of the QTF signal resulting from the nanomaterial-mediated interactions. The proposed and demonstrated novel FM-AFM technique provides high experimental sensitivity in the measurement of the viscoelastic forces associated with the confined nano-water meniscus, short response time, and insensitivity to amplitude noise, which are essential for precision dynamic force spectroscopy and microscopy.

Time-resolved observation of thermally activated rupture of a capillary-condensed water nanobridge

The capillary-condensed liquid bridge is one of the most ubiquitous forms of liquid in nature and contributes significantly to adhesion and friction of biological molecules as well as microscopic objects. Despite its important role in nanoscience and technology, the rupture process of the bridge is not well understood and needs more experimental works. Here, we report real-time observation of rupture of a capillary-condensed water nanobridge in ambient condition. During slow and stepwise stretch of the nanobridge, we measured the activation time for rupture, or the latency time required for the bridge breakup. By statistical analysis of the time-resolved distribution of activation time, we show that rupture is a thermally activated stochastic process and follows the Poisson statistics. In particular, from the Arrhenius law that the rupture rate satisfies, we estimate the position-dependent activation energies for the capillary-bridge rupture.

Nanopipette combined with quartz tuning fork-atomic force microscope for force spectroscopy/microscopy and liquid delivery-based nanofabrication

This paper introduces a nanopipette combined with a quartz tuning fork-atomic force microscope system (nanopipette/QTF-AFM), and describes experimental and theoretical investigations of the nanoscale materials used. The system offers several advantages over conventional cantilever-based AFM and QTF-AFM systems, including simple control of the quality factor based on the contact position of the QTF, easy variation of the effective tip diameter, electrical detection, on-demand delivery and patterning of various solutions, and in situ surface characterization after patterning. This tool enables nanoscale liquid delivery and nanofabrication processes without damaging the apex of the tip in various environments, and also offers force spectroscopy and microscopy capabilities.