Plasma-Assisted ALD of Highly Conductive HfNx: On the Effect of Energetic Ions on Film Microstructure

Plasma Chemistry and Plasma Processing - In this work, we report on the atomic layer deposition (ALD) of HfNx thin films by employing CpHf(NMe2)3 as the Hf(IV) precursor and Ar–H2 plasma in...     

High mobility In2O3:H transparent conductive oxides prepared by atomic layer deposition and solid phase crystallization

The preparation of high‐quality In₂O₃:H, as transparent conductive oxide (TCO), is demonstrated at low temperatures. Amorphous In₂O₃:H films were deposited by atomic layer deposition at 100 °C, after which they underwent solid phase crystallization by a short anneal at 200 °C. TEM analysis has shown that this approach can yield films with a lateral grain size of a few hundred nm, resulting in electron mobility values as high as 138 cm²/V s at a device‐relevant carrier density of 1.8 × 10²⁰ cm^–3. Due to the extremely high electron mobility, the crystallized films simultaneously exhibit a very low resistivity (0.27 mΩ cm) and a negligible free carrier absorption. In conjunction with the low temperature processing, this renders these films ideal candidates for front TCO layers in for example silicon heterojunction solar cells and other sensitive optoelectronic applications. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Quasi-ice monolayer on atomically smooth amorphous SiO2 at room temperature observed with a high-finesse optical resonator

The structure of an H(2)O monolayer bound to atomically smooth hydroxylated amorphous silica is probed under ambient conditions by near-infrared evanescent-wave cavity ring-down absorption spectroscopy. Employing a miniature monolithic optical resonator, we find sharp (approximately 10 cm(-1)) and polarized (>10:1) vibration-combination bands for surface OH and adsorbed H(2)O, which reveal ordered species in distinct local environments. Indicating first-monolayer uniqueness, the absorption bands for adsorbed H(2)O show intensity saturation and line narrowing with completion of one monolayer. Formation of the ordered H(2)O monolayer likely arises from H bonding to a quasicrystalline surface OH network.     

An improved two‐stage variance balance approach for constructing partial profile designs for discrete choice experiments

In many discrete choice experiments set up for product innovation, the number of attributes is large, which results in a substantial cognitive burden for the respondents. To reduce the cognitive burden in such cases, Green suggested in the early '70s the use of partial profiles that vary only the levels of a subset of the attributes. In this paper, we present two new methods for constructing Bayesian ‐optimal partial profile designs for estimating main‐effects models. They involve alternative generalizations of Green's approach that makes use of balanced incomplete block designs and take into account the fact that attributes may have differing numbers of levels. We refer to our methods as variance balance I and II because they vary an attribute with a larger number of levels more often than an attribute with fewer levels to stabilize the variances of the individual part‐worth estimates. The two variance balance methods differ in the way attributes with differing numbers of levels are weighted. Both methods provide statistically more efficient partial profile designs for differing numbers of attribute levels than another generalization of Green's approach that does not weight the attributes. This method is called attribute balance. We show results from an actual experiment in software development demonstrating the usefulness of our methods. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface passivation of phosphorus‐diffused n+‐type emitters by plasma‐assisted atomic‐layer deposited Al2O3

In recent years Al₂O₃ has received tremendous interest in the photovoltaic community for the application as surface passivation layer for crystalline silicon. Especially p‐type c‐Si surfaces are very effectively passivated by Al₂O₃, including p‐type emitters, due to the high fixed negative charge in the Al₂O₃ film. In this Letter we show that Al₂O₃ prepared by plasma‐assisted atomic layer deposition (ALD) can actually provide a good level of surface passivation for highly doped n‐type emitters in the range of 10–100 Ω/sq with implied‐V_oc values up to 680 mV. For n‐type emitters in the range of 100–200 Ω/sq the implied‐V_oc drops to a value of 600 mV for a 200 Ω/sq emitter, indicating a decreased level of surface passivation. For even lighter doped n‐type surfaces the passivation quality increases again to implied‐V_oc values well above 700 mV. Hence, the results presented here indicate that within a certain doping range, highly doped n‐ and p‐type surfaces can be passivated simultaneously by Al₂O₃. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Production mechanisms of NH and NH2 radicals in N2-H2 plasmas

We measured the densities of NH and NH(2) radicals by cavity ring-down spectroscopy in N(2)-H(2) plasmas expanding from a remote thermal plasma source and in N(2) plasmas to which H(2) was added in the background. The NH radical was observed via transitions in the (0,0), (1,1), and (2,2) vibrational bands of the A(3)Pi <-- X(3)Sigma- electronic transition and the NH(2) radical via transitions in the (0,9,0) <-- (0,0,0) band of the A(2)A(1) <-- X(2)B(1) electronic transition. The measurements revealed typical densities of 5 x 10(18) m(-3) for the NH radical in both plasmas and up to 7 x 10(18) m(-3) for the NH(2) radical when N(2) and H(2) are both fed through the plasma source. In N(2) plasma with H(2) injected in the background, no NH(2) was detected, indicating that the density is below our detection limit of 3 x 1016 m-3. The error in the measured densities is estimated to be around 20%. From the trends of the NH(x) radicals as a function of the relative H(2) flow to the total N(2) and H(2) flow at several positions in the expanding plasma beam, the key reactions for the formation of NH and NH(2) have been determined. The NH radicals are mainly produced via the reaction of N atoms emitted by the plasma source with H(2) molecules with a minor contribution from the reaction of N+ with H(2). The NH(2) radicals are formed by reactions of NH(3) molecules, produced at the walls of the plasma reactor, and H atoms emitted by the plasma source. The NH radicals can also be produced by H abstraction of NH(2) radicals. The flux densities of the NH(x) radicals with respect to the atomic radicals are appreciable in the first part of the expansion. Further downstream the NH(x) radicals are dissociated, and their densities become smaller than those of the atomic radicals. It is concluded that the NH(x) radicals play an important role as precursors for the N and H atoms, which are key to the surface production of N(2), H(2), and NH(3) molecules.     

Ammonia adsorption and decomposition on silica supported Rh nanoparticles observed by in situ attenuated total reflection infrared spectroscopy

Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) is applied to study NH₃, adsorbed from the gas phase, and its decomposition products, i.e. NH_x species, on Rh nanoparticles, produced by spincoating from a RhCl₃ solution in water followed by reduction. A silicon ATR crystal with a hydroxilated SiO₂ layer acts as the support for the nanoparticles. Upon exposure to NH₃ in the vacuum chamber, NH₃ adsorbed to both silica and Rh is detected (sensitivity ∼5 × 10⁻⁵ absorbance units). Interaction of the NH₃ with the silica OH groups is observed around ∼2840 cm⁻¹ in combination with peaks showing the disappearance of unperturbed OH vibrations between 3500 and 3700 cm⁻¹. In addition, NH bend vibrations at 1634 cm⁻¹ and NH stretch vibrations at 3065 and 3197 cm⁻¹ are observed for substrate temperatures between 20 and 100 °C. The latter two correspond to NH on Rh, as verified with a sample without Rh, and probably correspond to undecomposed NH₃. Moreover, they remain after evacuation, suggesting strongly bound species. For a substrate temperature of 75 and 100 °C, additional NH stretch peaks at 3354 and 3283 cm⁻¹ are observed, possibly due to NH₂ intermediates, indicating NH₃ decomposition. It is shown that ATR-FTIR can contribute to the sensitive detection of adsorption and decomposition of gaseous species on realistic planar model catalysts.