Hydride Precursors Research Articles

Kinetics and dynamics of Si GSMBE studied by reflectance anisotropy spectroscopy

Kinetic and dynamic information from semiconductor surfaces is of great importance in the understanding of growth processes in molecular beam epitaxy. Surface related information, such as coverage and composition, is often measured with techniques such as temperature programmed desorption under conditions away from those encountered in a realistic growth environment. If the adsorbate/precursor has a strong influence on the electronic structure of the surface it is possible to make in situ and more direct measurements using optical techniques. Reflectance anisotropy spectroscopy (RAS) has been shown to be sensitive to morphological, structural and chemical changes on the surface and is well-suited for this role. Structural changes on the Si(001) surface resulting from epitaxial growth were shown to be the origin of RA oscillations observed during layer by layer growth. Hydrogen produced on the surface from the decomposition of hydride precursors is very important in the growth of Si and SiGe, since it can prevent further adsorption of hydrides through site blocking, behave as a surfactant and change the spectroscopic RA response. We can use the single reconstruction domain produced on vicinal Si(001) surfaces to explore surface-hydride–hydrogen interactions. We have made isothermal measurements during adsorption and desorption cycles and compared the results with various models whose validity under the condition studied is discussed.

Reactivity of bis(alkene) tetracarbonyl complexes of tungsten: evidence for alkene to π-allyl hydride rearrangement

The bis(alkene)tetracarbonyl complexes of tungsten were identified as olefin isomerization and metathesis catalyst precursors whose activities are based on the formation of a π-allyl hydride intermediate. It has been observed that the β-hydrogen atom of coordinated olefin may migrate to the metal giving η 3-allylic hydrides which have been characterized by their 1H NMR spectra. This is the first case where the rearrangement of tungsten(0) alkenes coordinated to a π-allylic hydrides intermediate, fundamental to many catalytic mechanisms, can be observed directly. In the presence of Lewis acid the same alkene complexes are catalytically active toward olefin metathesis. It seems reasonable that the catalystically active alkylidene compounds are formed from the coordinated alkene via π-allylic hydride and metallacyclobutane precursors.

Metallisation of porous silicon by chemical vapour infiltration and deposition

Thin cobalt layers have been grown on and in porous silicon by chemical vapour infiltration and deposition using HCo(CO)4. The process can be controlled to give a capping layer with or without metal in the pores. Thin coats on the pore walls have been measured to depths of several μm and thick coats to depths of 0.1 μm.Results from mass spectroscopy indicate that when a cobalt hydride precursor molecule decomposes on a pore wall it releases its hydrogen atom accompanied by three from the pore wall, so forming direct metal-silicon bonds.

Reflectance anisotropy studies of the growth of InP on InP(001) at atmospheric pressures using tertiarybutylphosphine and trimethylindium

There is currently much interest in developing precursors for the vapour phase growth of compound semiconductors as alternatives to the hazardous group V hydride precursors arsine and phosphine. For InP growth in particular, the precursor tertiarybutyl phosphine (TBP) is known to perform well in terms of the quality of the resulting epilayers but little is known regarding the gas-phase or surface-phase chemistry of this compound. In order to study the surface chemistry under typical growth conditions, we have investigated the nature of the surface reactions that occur at atmospheric pressures when growing InP on InP(001) substrates from TBP and trimethylindium (TMIn) using the novel “epioptic” technique known as reflectance anisotropy (RA). Here we report the findings of experiments in which the interaction of TMIn (specifically) and TBP (indirectly) with the substrate surface were monitored at temperatures in excess of 300°C as they were introduced into a conventional growth reactor in a sequential manner, during an atomic layer epitaxy growth cycle. These experiments demonstrate clearly that the RA technique is a particularly powerful in-situ probe of growth kinetics.

The growth of InAlP using trimethyl amine alane by chemical beam epitaxy

The growth of InAlP and related compounds such as InGaP lattice matched to GaAs has attracted a great deal of interest for optoelectronic devices emitting in the range from 638 to 700 nm and for electronic devices such as the heterojunction bipolar transistor. Although some gas source MBE work has been performed in this material system, very little CBE work has been done, largely attributable to the lack of a suitable aluminum source. This is the first report of trimethyl amine alane (TMAA) being used to grow InAlP. TMAA offers advantages of less carbon incorporation and less oxygen sensitivity compared to triethyl aluminum, tri-isobutyl aluminum, or trimethyl aluminum. Trimethyl amine alane has been used to grow AlGaAs HBTs and more recently to grow InAlAs/InGaAs HEMTs by CBE. One of the principal strengths of CBE is its ability to handle phosphorus based compounds efficiently, offering excellent interface control. InAlP films with carbon concentrations below 7×10 17 cm -3 lattice matched |δa a|<2×10 -3 with good surface morphology have been grown. Double crystal X-ray diffraction exhibits a single epi-peak with a full width at half max of 46 arc sec with multiple Pendellösung fringes. The epitaxial films are semi-insulating, completely depleted for thicknesses up to 1.6 μm. Oxygen levels measured by secondary ion mass spectroscopy are comparable to levels measured in InAlAs films (∼2.5×10 18 cm -3) lattice matched to InP. The likely source of this oxygen is the hydride precursor as has been shown for the growth of InAlAs. As the substrate temperature is raised, the films become increasingly indium-rich. Breaking the growth rate down into its constituent binaries indicates an enhanced TMI incorporation rate. The quality of the films as measured by X-ray full width at half max and the surface morphology is extremely sensitive to substrate temperature. A very narrow window exists for the growth of good quality material in the range from 535 to 545°C.

New group III aluminium and gallium hydride precursors for metal-organic vapour-phase epitaxy

New group III hydride precursors have been synthesized in high yield and their purities have been measured by atomic absorption spectroscopy analysis, ion chromatography and metal-organic vapour-phase epitaxy. With these compounds, which have no metal-to-carbon bond, a decrease in carbon incorporation into (Al, Ga)As/GaAs heterostructures is achieved. The efficient combination of these sources with organoarsines at lower V-to-III ratios allows for a replacement of the highly toxic AsH 3 by new alternative group V precursors, which show remarkable lower toxicities.

Improved compositional uniformity of InGaAsP grown by low pressure metalorganic vapor phase epitaxy using tertiary butyl phosphine as the phosphorus source

We present the results of an investigation of the effect of group V precursor on the compositional uniformity of InGaAsP (λ = 1.35 μm) layers grown by low pressure metalorganic vapor phase epitaxy on 50 mm diameter substrates. The usual hydride precursors, AsH 3 and PH 3, and their organometallic counterparts, tertiary butyl arsine (TBAs) and tertiary butyl phosphine (TBP) were used in a variety of combinations. Lattice mismatch and photoluminescence mapping of the wafers were used to calculate the values of x (Ga mole fraction) and y (As mole fraction) in the resulting In 1− x Ga x As y P 1− y films. It was found t hat the value of x varied by ∼1% across the wafer area for all group V source combinations but that the variation in the value of y improved from 2.8 −2.9% for both the AsH 3 + PH 3 and TBAs + TBP source combinations to 1% for the AsH 3 + TBP source combination. This corresponded to a decrease in photoluminescence wavelength variation of 30 nm for the AsH 3 + PH 3 combination to 10 nm for the AsH 3 + TBP combination. Furthermore, it was found that the V/III ratio at which specular surfaces could be attained decreased from ∼80 in the case of AsH 3 + PH 3 to <20 with either AsH 3 + TBP or TBAs + TBP and that the relative P incorporation increased in the source combination sequence of AsH 3 + PH 3 <TBAs + TBP < AsH 3 + TBP.

Crystal structures of the PPN salts of the anions trans-[SiCl 3(PPh 3) Fe(CO) 3] − and trans-[SiCl 3{P(OPH) 3}Fe(CO) 3] −

PPN salts of [SiCl 3(PPh 3)Fe(CO) 3] − ( I) and [SiCl 3{P(OPh) 3}Fe(CO) 3] − ( II) have been prepared by literature procedures from the hydride precursors. Each crystallizes in the monoclinic space group P2 1 /c with the following respective unit cell constants: I, a = 16.087(3), b = 15.334 (2), c = 22.804(2) Å, β = 109.45(1)°, V = 5304.0(1) Å 3, Z = 4; II, a = 18.623(3), b = 13.449(6), c = 23.447(6) Å, β = 109.91(2)°, V = 5528.8 (1) Å 3, Z = 4. Both anions are trigonal bipyramidal with the silicon and phosphorus ligands in the axial positions.

Utilisation des ligands aminophosphinephosphinites en hydroformylation catalysée par le rhodium: amélioration de l'énantioselectivité par synthèse selective des hydrures RhH(CO) 2L ★2

Asymmetric hydroformylation of styrene by rhodium catalysts modified with aminophosphinephosphinite ligands has been studied. Use of either Rh 4(CO) 12/L ★ 2 mixture or RhClCOL ★ 2 in electroreduction under CO/H 2, gives interesting results in respect of regio- (PhCHMeCHO/PHCH 2CH 2CHO) and enantio-selectivity when the ligands (1 R,2 S)-PPh 2NMeCHMeCHPhOPPh 2 and (CH 3) 2C(N(Me)PPh 2)-HCH 2OPPH 2 (e.e. > 30%) are used. 1H and 31P NMR spectroscopy has indicated the occurrence of the RhH(CO) 2L ★ 2 hydride precursor, suggested to be responsible for catalysis. It is a trigonal complex having an aminophosphine function in a trans position to the hydrogen, the equatorial position being occupied by the (PO) group and the two CO moieties.

Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen: XVI. Doppelte oxidative addition von monosilan an das koordinativ ungesättigte organometall-fragment (η 5-C 5Me 5)Mn(CO) 2: Darstellung und molekülstruktur von μ-silylen-bis[dicarbonyl(hydrido)(η 5-pentamethylcyclopentadienyl)mangan

Upon treatment of the labile ether complex (η 5-C 5Me 5)Mn(CO) 2(THF) ( 1) with monosilane the novel dinuclear complex of composition (μ-SiH 2)[(η 5-C 5Me 5)Mn(CO) 2H] 2 ( 2) is formed in 15% isolated yield via double oxidative addition of the binary hydride precursor. According to a single-crystal X-ray diffraction study, the molecule exhibits a bent MnSiMn′ framework (≮Mn, Si, Mn′ 124.4(3)°), with the manganese—silicon bond lengths representing single bonds (243.4(3) pm). The resulting distance of 430.6 pm between the manganese atoms precludes any metal—metal bonding so that the complex fragments (η 5-C 5Me 5)Mn(CO) 2H are exclusively connected to each other via the bridging silylene ligand. The hydrogen ligands attached to the manganese atoms could not be located by X-ray diffraction methods but were detected by NMR spectroscopy (δ(SiH) 4.59, δ(MnH) −11.55; CDCl 3). Although thermolysis of 2 yields elemental hydrogen, the expected and hitherto unknown complex (μ-Si)[(η 5-C 5Me 5)Mn(CO) 2] 2 is not observed.