Jong Shik Jang

In Situ Determination of the Pore Opening Point during Wet-Chemical Etching of the Barrier Layer of Porous Anodic Aluminum Oxide: Nonuniform Impurity Distribution in Anodic Oxide

Wet-chemical etching of the barrier oxide layer of anodic aluminum oxide (AAO) was systematically investigated by using scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and a newly devised experimental setup that allows accurate in situ determination of the pore opening point during chemical etching of the barrier oxide layer. We found that opening of the barrier oxide layer by wet-chemical etching can be significantly influenced by anodization time (tanodi). According to secondary ion mass spectrometry (SIMS) analysis, porous anodic aluminum oxide (AAO) samples formed by long-term anodization contained a lower level of anionic impurity in the barrier oxide layer compared to the short-term anodized one and consequently exhibited retarded opening of the barrier oxide layer during the wet-chemical etching. The observed compositional dependence on the anodization time (tanodi) in the barrier oxide layer is attributed to the progressive decrease of the electrolyte concentration upon anodization. The etching rate of the outer pore wall at the bottom part is lower than that of the one at the top part due to the lower level of impurity content in that region. This indicates that a concentration gradient of anionic impurity in the outer pore wall oxide may be established along both the vertical and radial directions of cylindrical pores. Apart from the effect of electrolyte concentration on the chemical composition of the barrier oxide layer, significantly decreased current density arising from the lowered concentration of electrolyte during the long-term anodization (~120 h) was found to cause disordering of pores. The results of the present work are expected to provide viable information not only for practical applications of nanoporous AAO in nanotechnology but also for thorough understanding of the self-organized formation of oxide nanopores during anodization.

Active doping of B in silicon nanostructures and development of a Si quantum dot solar cell

Active doping of B was observed in nanometer silicon layers confined in SiO(2) layers by secondary ion mass spectrometry (SIMS) depth profiling analysis and confirmed by Hall effect measurements. The uniformly distributed boron atoms in the B-doped silicon layers of [SiO(2) (8 nm)/B-doped Si(10 nm)](5) films turned out to be segregated into the Si/SiO(2) interfaces and the Si bulk, forming a distinct bimodal distribution by annealing at high temperature. B atoms in the Si layers were found to preferentially substitute inactive three-fold Si atoms in the grain boundaries and then substitute the four-fold Si atoms to achieve electrically active doping. As a result, active doping of B is initiated at high doping concentrations above 1.1 × 10(20) atoms cm( - 3) and high active doping of 3 × 10(20) atoms cm( - 3) could be achieved. The active doping in ultra-thin Si layers was implemented for silicon quantum dots (QDs) to realize a Si QD solar cell. A high energy-conversion efficiency of 13.4% was realized from a p-type Si QD solar cell with B concentration of 4 × 10(20) atoms cm( - 3).

A method to determine the interface position and layer thickness in SIMS depth profiling of multilayer films

The measurement of layer thickness by compositional secondary ion mass spectrometry (SIMS) depth profiling is investigated for Si/Ge multilayer films using an oxygen ion beam. The original SIMS depth profiles were converted into compositional depth profiles by the relative sensitivity factors of Si and Ge derived from a Si52.4Ge47.6 alloy reference film. The locations of the interfaces in the Si/Ge multilayer films could be well determined by 50 at% definition where the relative composition of the constituent layer elements drops or rises to 50 at%. The layer thicknesses of Si and Ge of a test Si/Ge multilayer film were determined by the sputtering rates of Si and Ge determined from a reference Si/Ge multilayer film. Although the difference between the measured and the actual thicknesses is increased as the ion energy is increased, the layer thicknesses determined at low ion energies were very close to the actual values.

Determination of the absolute thickness of ultrathin Al2O3 overlayers on Si (100) substrate.

The thickness of nanometer Al(2)O(3) films was studied by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The thickness was determined from mutual calibration of the XPS and TEM measurements. The thickness offset of Al(2)O(3) films was proved to be close to zero by in situ XPS analysis. The thicknesses of a series of Al(2)O(3)/Si (100) films with different Al(2)O(3) thicknesses could be determined by mutual calibration from the thicknesses measured by TEM and XPS. The electron attenuation length of the Al 2p electron was determined as 2.4334 nm in the Al(2)O(3) matrix.

Accurate determination of the surface normal for the reliable measurement of ultra-thin SiO2 thickness by x-ray photoelectron spectroscopy

Measurement of the thickness of SiO2 films on crystalline Si substrates was the subject of the key comparison (K-32) of the Surface Analysis Working Group of the Consultative Committee for Amount of Substance. X-ray photoelectron spectroscopy (XPS) gave the most reproducible results that are consistent with other reflectivity based methods. In addition, XPS is free from surface contamination effects. However, the emission angle of photoelectrons is one of the main sources of the uncertainty in the measured thickness. In this report, we propose a simple and reliable procedure to determine the surface normal for accurate control of the emission angle using an amorphous SiO2 overlayer on an amorphous Si substrate. The surface normal can be accurately determined from the condition that the estimated thickness of a SiO2 overlayer on an amorphous Si substrate measured must be the same for different emission angles. With the proposed calibration procedure, the surface normal can be determined precisely and the uncertainty of the electron emission angle can be evaluated.

A mutual calibration method to certify the thickness of nanometre oxide films

In a recent study on the measurement of SiO2 film thickness on a silicon substrate, the thicknesses measured by various methods showed large offset values, giving an apparent thickness when the real thickness was extrapolated to zero. Compensation of these offset values is a key solution for the establishment of traceability in the measurement of SiO2 film thickness. In this study, a mutual calibration method is suggested as a new method to certify the thickness of SiO2 films on Si by compensating for the offset values. In a linear plot of the thicknesses measured by x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) of a series of SiO2 films with different thicknesses, the offset value of TEM and the thickness scale of XPS can be mutually calibrated. Using this method, the XPS photoelectron attenuation length can be well defined and XPS becomes traceable in the measurement of the thickness of SiO2 films.