Device-quality Films Research Articles

Possible Diffusion of Molecular Hydrogen Along Microvoids in Device-Quality a-Si:H

AbstractA comparison of 1H nuclear magnetic resonance (NMR) measurements in freshly prepared a-Si:H films on substrates with those removed from the substrates shows that a large fraction of the trapped H2 molecules are released when the films are removed from the substrates. After the films on substrates have been aged for several months, an equal amount of H2 has diffused out of the film. This gradual aging appears-to stabilize after several months. Once aged, H2 can be diffused into the films by immersion in H2 gas. The diffusion time is around 2 weeks at 300 K which is much slower than in vitreous quartz or 7059 glass at the same temperature. Diffusion, which is enhanced during the aging process, could proceed via the remnant columnar structure in the film. This speculation is supported by the inability to detect, using pake-doublet experiments, significant changes in the H2 content and by the recent observation of oxygen diffusion along remnant columnar structure in device quality films.

Investigation of hexagonal ferrite substrate and film growth

Hexagonal ferrites with large anisotropy fields can operate close to resonance at mm-wave frequencies. The growth of device-quality hexagonal ferrite films depends on the availability of lattice-matched substrates and optimized film deposition methods. Several potential substrate candidates were identified and characterized. Two promising materials, Ba <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (VO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and CoGa <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> were chosen for detailed study by LPE growth of hexaferrite films. Under the LPE growth conditions so far investigated, either no film nucleated on the Ba <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (VO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> or the substrates reacted with the melts. LPE layers were successfully grown on CoGa <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> substrates. There was an interdiffused layer at the interface of the hexaferrite film and CoGa <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> substrate. To obtain device-quality films on SrGa <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</inf> substrates (used for comparison), both film and substrate lattice parameters had to be adjusted by chemical substitution.

Device quality AlGaAs/GaAs heterostructures grown in a multichamber organometallic vapor phase epitaxial apparatus

The use of a vertical multichamber organometallic vapor phase epitaxial (OMVPE) reactor for the growth of compound semiconductors is described. The formation of abrupt AlGaAs/GaAs heterostructures has been achieved by positioning the substrates by rotation in growth zones with the appropriate combinations of the sources; trimethylgallium, trimethylaluminum, and arsine. Photoluminescence, Raman spectroscopy, and cross-sectional transmission electron microscopy are used to demonstrate the optical quality and structural properties of the epitaxial films produced by this variation of the OMVPE technique. Device quality films are demonstrated by the fabrication of all superlattice separate confining laser structures emitting over the wavelength range from 740 to 855 nm.

Multiple-quantum NMR study of clustering in hydrogenated amorphous silicon.

Multiple-quantum nuclear-magnetic-resonance techniques are used to study the distribution of hydrogen in hydrogenated amorphous silicon. Using the fact that multiple-quantum excitation is limited by the size of the dipolar-coupled spin system, we show that the predominant bonding environment for hydrogen is a cluster of four to seven atoms. For device-quality films, the concentration of these cluster defects increases with increasing hydrogen content. At very high hydrogen content, the clusters are replaced with a continuous network of silicon-hydrogen bonds.

Multiple Quantum NMR Study of Hydrogen Clustering in Amorphous Silicon

ABSTRACTBecause Multiple Quantum NMR coherences occur only between spins which are coupled together by the dipole interaction, this technique has been used to study the clustering of hydrogen in amorphous silicon. The clustered hydrogen was found to be associated with the broad line of the single quantum NMR spectra. For device quality films, the average cluster size is approximately six protons. The concentration of these five to seven atom defects increases with increasing hydrogen content until, at very high hydrogen content, the clusters are replaced by a continuous network of silicon-hydrogen bonds.