Charles W. Teplin

High-mobility transparent conducting Mo-doped In2O3 thin films by pulsed laser deposition

Highly conductive and transparent Mo-doped indium oxide (IMO) thin films were grown on glass and (100) yttria-stabilized zirconia (YSZ) single-crystal substrates by pulsed laser deposition. The electrical, optical, and structural properties were measured for films grown from 0, 1, 2, and 4 wt % Mo-doped targets. Films grown from the 2 wt % Mo-doped target had the best overall properties. In particular, for biaxially textured 2 wt % Mo IMO films grown on (100) YSZ, the conductivity was ∼3000 S cm−1 with a mobility greater than 95 cm2 V−1 s−1. In the visible, the optical transmittance normalized to the substrate was greater than 90%.

Material structure and metastability of hydrogenated nanocrystalline silicon solar cells

We find that the volume fraction of amorphous component in hydrogenated nanocrystalline silicon intrinsic layers is not necessarily the determining factor for the light-induced metastability ofn-i-p solar cells. Small grains and/or intermediate range order may play an important role in improving the stability. The distribution of nanocrystallites along the growth direction is also important. Based on the findings, we have optimized the hydrogen dilution profiling for controlling the structural evolution and have reduced the light-induced degradation of solar cells. As a result, we have achieved initial and stable active-area efficiencies of 14.1% and 13.2%, respectively, using ana-Si:H/nc-Si:H/nc-Si:H triple-junction structure.

Subnanosecond magnetization dynamics measured by the second-harmonic magneto-optic Kerr effect

We have measured the in-plane magnetization dynamics of Ni81Fe19 films using the surface- and interface-sensitive second-harmonic magneto-optic Kerr effect. The dynamical magnetization was measured on patterned Ni81Fe19 stripes as a function of an in-plane magnetic field applied parallel to the anisotropy axis. The excitation sources were 100 ps risetime magnetic field impulses and steps. The minimum magnetization switching times were <300 ps, and precessional free-induction decay was observed. The dynamics for both impulse and step excitation are fitted to the Landau–Lifshitz equation, yielding values for the anisotropy field, gyroscopic splitting factor, and damping. The local surface precessional frequency and anisotropy are different from the average bulk values, demonstrating that this technique possesses the necessary sensitivity to detect variations in localized surface and interface dynamics.

Optical surface second harmonic measurements of isotropic thin-film metals: Gold, silver, copper, aluminum, and tantalum

We have studied optical surface second harmonic generation and have determined the magnitude and relative phase of the second-order susceptibility tensor elements for thermally evaporated gold, and sputtered silver, copper, aluminum, and tantalum. The second harmonic data are understood using an isotropic model of the surfaces. The measurements of the parameters from this nonlinear optical characterization, in conjunction with linear optical characterization of the samples, allow us to extract the elements of the tensors. The typical size of χ⊥(2), the tensor element that produces the surface current perpendicular to the surface and is the largest surface element, ranges from 3(±1)×10−12cm2∕statvolt for an aluminum sample with 24(±4)Arms surface roughness to 1.1(±0.1)×10−13cm2∕statvolt for a copper sample with 5(±1)Arms surface roughness. Film preparation and associated surface roughness can reproducibly change the values of χ(2); increasing sample roughness increases the magnitudes of the tensor elements...

The electrical, optical and structural properties of InxZn1−xOy (0 ⩽ x ⩽ 1) thin films by combinatorial techniques

Indium–zinc-oxide (IZO) compositional libraries were deposited with dc magnetron sputtering onto glass substrates at 100 °C and analysed with high throughput, combinatorial techniques. The composition range from 4 to 95 at% In for Zn was explored. A peak in conductivity with σ > 3000 (Ω cm)−1 was observed at an indium content of ~70%. The mobility exceeded 30 cm2 (V s)−1 and the carrier concentrations were greater than 8 × 1020 cm−3. Crystalline phases were observed for In concentrations less than 45% and greater than 80% with an intermediate amorphous region. The low indium content films have a zinc oxide type structure with a ZnO (002) spacing ranging from ~2.61 to 2.85 A for 4% In and 45% In, respectively. For indium contents between 82% and 95%, the In2O3 (222) spacing varied from 2.98 to 2.99 A. Regardless of the composition or the degree of crystallinity, all films showed high optical transparency with the transmission >80% across the visible spectrum.

Material quality requirements for efficient epitaxial film silicon solar cells

The performance of 2-μm-thick crystal silicon (c-Si) solar cells grown epitaxially on heavily doped wafer substrates is quantitatively linked to absorber dislocation density. We find that such thin devices have a high tolerance to bulk impurities compared to wafer-based cells. The minority carrier diffusion length is about half the dislocation spacing and must be roughly three times the absorber thickness for efficient carrier extraction. Together, modeling and experimental results provide design guidelines for film c-Si photovoltaic cells.

A simple method for the preparation of transparent p-type Ca-doped CuInO2 films: Pulsed-laser deposition from air-sintered Ca-doped Cu2In2O5 targets

We report the deposition of single-phase undoped and Ca-doped CuInO2 thin films from a readily synthesized source target of Cu2In2O5—circumventing the very difficult fabrication of CuInO2 targets. X-ray diffraction shows that single-phase materials were obtained over a range of substrate temperatures and deposition pressures. p-type conductivities are measured to be ∼3×10−3S∕cm, comparable to the best films previously reported. The optical properties of the films were measured by spectroscopic ellipsometry.

Heteroepitaxial film silicon solar cell grown on Ni-W foils

Heteroepitaxial semiconductor films on low-cost, flexible metal foil templates are a potential route to inexpensive, high-efficiency solar cells. Here, we report epitaxial growth of Si films on low-cost, flexible, biaxially-textured Ni-W substrates. A robust buffer architecture comprised of multiple epitaxial oxide layers has been developed to grow high quality, heteroepitaxial Si films without any undesired reaction between the Si film and the metal substrate and with a single biaxial texture. XRD analysis including ω-scans, φ-scans, and pole figures confirms that the buffers and silicon are all epitaxial, with excellent cube-on-cube epitaxy. A photo-conversion efficiency of 1.1% is demonstrated from a proof-of-concept heteroepitaxial film Si solar cell.

Monitoring and modeling silicon homoepitaxy breakdown with real-time spectroscopic ellipsometry

Real-time spectroscopic ellipsometry (RTSE) is used to monitor the breakdown of low-temperature homoepitaxial growth of silicon on silicon wafers in a hot-wire chemical-vapor deposition reactor. We develop and evaluate two optical models to interpret the RTSE data, revealing the progression of epitaxy and its eventual breakdown into amorphous silicon growth. Comparison of the RTSE analysis with cross-sectional transmission electron microscopy, ex situ variable-angle spectroscopic ellipsometry, and Raman spectroscopy measurements shows that RTSE provides accurate and fast quantitative feedback about the progression of epitaxy.

Significant improvement in silicon chemical vapor deposition epitaxy above the surface dehydrogenation temperature

We observe an order of magnitude increase in both the rate and achievable thickness of epitaxy by hot-wire chemical vapor deposition at temperatures above the dehydrogenation temperature of the silicon surface. We deposit silicon films on (100) silicon at 110nm∕min at substrate temperatures between 520 and 645°C. At the glass compatible temperature of 610°C, we observe phase-pure epitaxial growth of more than 10μm, as observed by x-ray diffraction and transmission electron microscopy, in contrast to the mixed-phase breakdown seen at lower temperatures. In 610°C films thicker than 4μm, a stable (100)-epitaxial growth mode produces regular surface pyramids with vicinal ⟨311⟩ facets. On the low-energy (111) face of Si, more than 2μm of epitaxial Si were grown at 645°C, but some twinning is observed. The temperature of this new growth regime suggests that rapid dehydrogenation of the growing surface is critical for silicon epitaxy by CVD.