Matthew S. Dabney

Titanium-doped indium oxide: A high-mobility transparent conductor

We report on the effects of titanium doping (0–7at.%) on the optical and electrical properties of In2O3 using combinatorial deposition and analysis techniques. Maximum mobilities are observed at Ti concentrations of 1.5–2.5at.% and are >80cm2∕Vs in sputtered films. The carrier concentration increased with titanium content to a high of 8.0×1020cm−3. Data show that one carrier is generated per added Ti between 1 and 3at.%. Conductivities up to 6260Ω−1cm−1 were observed. These remained very high >5000Ω−1cm−1 across a wide compositional range. The optical transparency is high (>85%) in a wide spectral range from 400nm to at least 1750nm. The work function of titanium-doped indium oxide varies substantially over the studied compositional range.

rf magnetron sputter deposition of transparent conducting Nb-doped TiO2 films on SrTiO3

rf magnetron sputtering, an established and scalable large area deposition process, is used to deposit Nb:TiO2 and Ta:TiO2 films onto (100) SrTiO3 substrates at temperatures TS ranging from room temperature to 400°C. Optical, electrical, and structural properties similar to those reported for pulsed laser deposition grown films were obtained. In particular, the most conducting Ti0.85Nb0.15O2 films, grown at TS≈375°C, are epitaxially oriented anatase films with conductivity of 3000Scm−1, carrier concentration of 2.4×1021cm−3, Hall mobility of 7.6cm2V−1s−1, and optical transparency T>80% from 400to900nm. The conductivity is strongly correlated with the intensity of the anatase (004) x-ray diffraction peak.

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.

Direct write contacts for solar cells

Ag, Cu and Ni metallizations were inkjet printed with near vacuum deposition quality. The approach developed can be easily extended to other conductors such as Pt, Pd, Au etc. Thick highly conducting lines of Ag and Cu demonstrating good adhesion to glass, Si and PCB have been printed at 100-200 /spl deg/C in air and N/sub 2/ respectively. Ag grids were inkjet-printed on Si solar cells and fired through the silicon nitride AR layer at 850 /spl deg/C resulting in 8% cells. Next generation multicomponent inks (including etching agents) have also been developed with improved fire through contacts leading to higher cell efficiencies. PEDOT-PSS polymer based conductors were inkjet printed with conductivity as good or better than that of spin-coated films.

Combinatorial study of reactively sputtered Cr-Ti-N

Abstract A combinatorial study of ternary Cr–Ti–N libraries is reported. Sixteen libraries were grown with a range of metallic composition gradients and different nitrogen contents. X-ray photoelectron spectroscopy (XPS) and electron microprobe analysis (EPMA) show that these libraries encompass a large portion of the ternary phase space. Optical transmission and reflection measurements from near ultra-violet to infra-red wavelengths suggest that both the color and infra-red reflectivity can be optimized for this ternary system.

Altering the Nucleation of Thermally Annealed Hydrogenated Amorphous Silicon with Laser Processing

We demonstrate the use of laser processing to affect the nucleation of crystallites in thermally annealed hydrogenated amorphous silicon (a-Si:H) thin films. The influence of film H content and subcrystallization threshold laser fluence are investigated by x-ray diffraction measurements during in situ thermal annealing at 600 °C. All laser-treated films show a reduced incubation time for crystallization compared to as-grown films, with the largest differences exhibited for samples with higher film H and higher laser fluences. These results are consistent with multivacancy annihilation by laser processing, based upon a recently developed model for a nucleation center in a-Si:H.

Combinatorial optimization of transparent conducting oxides (TCOs) for PV

Transparent conducting oxides (TCOs) can serve a variety of important functions in thin film photovoltaics such as transparent electrical contacts, antireflection coatings and chemical barriers. Two areas of particular interest are TCOs that can be deposited at low temperatures and TCOs with high carrier mobilities. We have employed combinatorial high-throughput approaches to investigate both these areas. Conductivities of /spl sigma/ = 2500 /spl Omega//sup -1/-cm/sup -1/ have been obtained for In-Zn-O (IZO) films deposited at 100/spl deg/C and /spl sigma/ > 5000 /spl Omega//sup -1/-cm/sup -1/ for In-Ti-O (ITiO) and In-Mo-O (IMO) films deposited at 550/spl deg/C. The highest mobility obtained was 83 cm/sup 2//V-sec for ITiO deposited at 550/spl deg/C.

The use of optical microscopy to examine crystallite nucleation and growth in thermally annealed plasma enhanced chemical vapor deposition and hot wire chemical vapor deposition a-Si:H films

We report a simple method to investigate crystallite nucleation and growth in stepwise, thermally annealed plasma enhanced chemical vapor deposition and hot wire chemical vapor deposition a-Si:H films. By confining film thicknesses to the range 500–4000 A, optical microscopy in the reflection mode can be used to readily detect crystallites in the thermally annealed a-Si:H lattice. Measurements of the crystallite density versus annealing time for identically prepared films of different thickness show that the crystallite nucleation rate is smaller for thinner films, suggesting that crystallite nucleation is homogeneous, in agreement with previous results. A comparison of film nucleation rates with those obtained by other methods on identically prepared films shows excellent agreement, thus establishing the validity of the current technique. The potential effect of impurity (oxygen) incorporation during the stepwise annealing in air is shown not to affect crystallite nucleation and growth, in that SIMS oxyg...

Printed monolithic interconnects for photovoltaic applications

Monolithic interconnects in photovoltaic modules connect adjacent cells in series, and are typically formed sequentially, involving multiple deposition and scribing steps. Interconnect widths on the order of 500 μm every 10 mm result in about 5% dead area, which does not contribute to power generation in an interconnected solar panel. This work introduces an alternative interconnection method capable of producing interconnect widths of less than 100 μm, which can be accomplished in a single pass after deposition of active layers and electrodes. This alternative method can be used for all types of thin film photovoltaics. Voltage addition using printed interconnects and ongoing efforts to optimize performance of modules with printed interconnect are discussed.

Nucleation rate reduction through stress relief of thermally annealed hydrogenated amorphous silicon films

The effect of film stress on crystallite nucleation is investigated in 0.11  μm thick, thermally annealed hydrogenated amorphous silicon films. Using a recently developed optical method, the crystallite density is measured as the films are isochronally annealed at 600 °C, which enables the determination of the crystallite nucleation rate. This rate is significantly suppressed around scratches, cleaved film edges, and laser ablated areas, extending laterally as much as 100–150 μm from these regions where the film connectivity is disrupted. μ-Raman measurements of the transverse optical mode of Si demonstrate an accompanying reduction in tensile stress in the regions where nucleation is suppressed. The first measurements of nucleation rate in stress and in stress relieved areas in the same film are presented.