J.E. Bourée

Pyrolysis pathways and kinetics of thermal decomposition of diethylzinc and diethyltellurium studied by mass spectrometry

The thermal decomposition of diethylzinc (Et2Zn) and diethyltellurium (Et2Te) has been studied both separately and combined using an isothermal reactor attached to a quadrupole mass spectrometer (QMS). Under helium and hydrogen atmospheres the decomposition of Et2Zn leads to ethene, ethane and n-butane; with D2 as a carrier gas C2H5D is produced. Pyrolysis of Et2Te leads to ethane and ethene only. With helium as the carrier gas, the activation energy for the pyrolysis was E ≈ 52 kcal mol–1 for Et2Zn and E ≈ 50 kcal mol–1 for Et2Te, firstorder kinetics being assumed. Under a hydrogen atmosphere, the determination of the activation energy for the pyrolysis of Et2Zn was inaccurate with a first-order reaction rate, and the activation energy for the pyrolysis of Et2Te was reduced to E ≈ 47 kcal mol–1. In the co-pyrolysis, which is close to the conditions of ZnTe growth, the principal trends are enhancement of Et2Te decomposition and an increase of the thermal stability of Et2Zn.

Photo-assisted growth of ZnTe by metalorganic chemical vapour deposition

Abstract The metalorganic chemical vapour deposition (MOCVD) photo-assisted growth of ZnTe using a xenon lamp has been performed at atmospheric pressure under hydrogen as a carrier gas. Epitaxial growth was achieved on (100) GaAs, (100) GaSb and (100) ZnTe substrates with diethylzinc (DEZn) and diethyltellurium (DETe) as precursors. We have studied the growth rate as a function of the growth temperature, the partial pressure of precursors, the inlet partial pressure ratio R = VI/II, the light intensity and the energy of the irradiating photons. A growth rate enhancement has been observed for illuminated layers grown on GaAs and ZnTe substrates in comparison with those grown without illumination. We have not observed any measurable enhancement for layers grown onto (100) GaSb. The growth rate as a function of the light intensity increases for intensities higher than 20 mW / cm 2 and saturates for P > 120 mW / cm 2 . We relate the growth rate enhancement to irradiating photons with an energy higher than the band gap of ZnTe at the growth temperature.

Growth kinetics during metal-organic chemical vapour deposition of ZnTe

Abstract ZnTe films are grown by metal-organic chemical vapour deposition starting from pyrolysis of a mixture of diethylzinc (DEZn) and diethyltellurium (DETe) diluted with H2. The decomposition process of these two organometallic precursors is monitored with a mass spectrometer; DEZn leads to n− C 4 H 10 with other hydrocarbons (C2H4 and C2H6) as reaction products and DETe leads to C2H4. When both organometallic precursors are present, a strong hysteresis loop of the signal intensity when heating and cooling the susceptor has been recorded, as a result of a catalytic reaction between the gas phase and the surface. The experimental growth rate V at 400 °C vs. organometallic concentration is described in terms of a kinetic model involving pyrolysis processes and a surface-catalysed reaction. The model explains the asymmetric behaviour of V; for a given DETe pressure (10−4 atm), the ZnTe growth rate as a function of DEZn partial pressure passes through a maximum ( p max DEZn ≈ 10 −4 atm ; V max ≈ 2.4 μ m h −1 ), whereas, at the same constant DEZn partial pressure, V follows a sublinear law with the increase in DETe partial pressure and saturates to V = 4.3 μ m h −1 .

In situ reflectance anisotropy studies of the growth of CdTe and other compounds by MOCVD

Using reflectance anisotropy (RA), we investigate in situ the metal-organic chemical vapor deposition (MOCVD) of CdTe and ZnTe on GaAs (100). RA transient signatures are observed at the beginning of the heteroepitaxy of lattice-mismatched semiconductors: CdTe on ZnTe and ZnTe on GaAs. RA records also exhibit a fast initial variation (δ/r=10−3) during the homoepitaxial growth of these II–VI compounds. In order to clearly understand those phenomena, surface coverage is analyzed by alternating the precursor flows. Large RA signals (δ/r=10−2) correlated with the 3D growth of ZnTe on GaAs are observed, before the material relaxation. These signals can be interpreted in terms of surface roughness evolution within the framework of the effective medium theories (EMT). Moreover, ex situ spectroscopic measurements of CdTe layers are performed and simulated; a good agreement is obtained between EMT models and experiments.

Metal photodeposition and light-induced nucleation

Abstract A framework for phenomenological understanding has been developed using aluminium deposition from metal alkyl as an example. UV sources are shown to be an efficient means to enhance the creation of active sites for heterogeneous nucleation at low temperatures. However, the continuity of a laser-written metal line is disturbed and even stopped by nucleation of carbon containing species. The use of scavenger gases, such as hydrogen, improves the continuity, and the high aspect ratio of direct-written lines. This approach renders this new process available for applications.

Photoassisted metal organic vapour-phase epitaxy of ZnTe on GaAs

Abstract Photoassisted epitaxy of ZnTe on GaAs by a metal organic vapour-phase process has been performed using sources of diethylzinc and diethyltellurium or diisopropyltellurium. Illuminating the layer during growth with a xenon lamp increases the growth rate. Growth rate enhancement was found to be a function of light wavelength and intensity. Only photons having energy higher than the bandgap of ZnTe increase the growth rate. The characterization of the layers by X-ray diffraction and of the surface morphology by Nomarski microscopy is reported. We observed the degradation of the surface morphology of irradiated layers in comparison with unilluminated layers. We tentatively explain the growth rate enhancement by a photocatalytic surface process involving electron - hole pairs created in the ZnTe layers.

Metalorganic vapour phase epitaxy growth of Zn1-xMgxTe layers

We report on metalorganic vapour phase epitaxy (MOVPE) growth of the IIa-VI compound MgTe and the variable band gap ternary semiconductor Zn 1−x Mg x Te. Bulk MgTe shows wurtzite type structure and is a direct band gap material (∼3.5 eV). The precursors used in this study were diisopropyltellurium (DIPTe), diethylzinc (DEZn) and bis-methylcyclopentadienylmagnesium (MCP 2 Mg). The growth of MgTe on (100) GaAs substrates was found to be polycrystalline. The films were very quickly degraded by hydratation, even if they were covered by a ZnTe film. Zn 1−x Mg x Te epitaxial layers on (100) GaAs were grown with a Mg concentration of 0 < x < 0.6. In that range of composition they appeared stable in air. For 0 < x < 0.5, the thin films showed zincblende structure and followed Vegards law. The crystalline parameters were determined by the measurement of the relative position of the (004) X-ray reflection of the substrate and of the layer. The crystalline quality of the layers of Zn 1−x Mg x Te alloys was comparable to pure ZnTe. Photoluminescence measurements exhibited a deep emission in the green region

Kinetics of laser thermal decomposition of trimethylamine alane

Abstract Using a focused Ar ion laser emitting at 514 nm, aluminum dots have been deposited on silicon-coated quartz substrate via a pyrolytic decomposition of trimethylamine alane. The growth kinetics of these Al dots was investigated as a function of the precursor pressure (1 to 7.5 mbar) and the laser-induced temperature. The threshold temperature for the onset of growth was observed to be 210°C. Deposition rates as high as 3 μm/s have been obtained at temperatures of about 300°C and were found to be independent of the precursor partial pressure. The activation energy of the deposition process was determined to be 18 kcal/mol. In order to understand the growth mechanism of these dots, several elementary steps occurring at the aluminum surface have been assumed involving AlH3 as well as AlH2 and AlH adspecies. From this study it is concluded that the desorption of the hydrogen molecules is the rate-limiting step in the laser chemical vapor deposition of Al from trimethylamine alane.

Laser-induced deposition of aluminium on gallium arsenide and silicon nitride from trimethylamine alane

Abstract Aluminium is a highly conductive metal, which is extensively used in the microelectronics industry for semiconductor and interconnect technology. Laser-induced chemical vapour deposition is a very attractive technique for the direct writing of micron-sized aluminium features of high quality with high deposition rates. The use of a solid precursor, an adduct called trimethylamine alane (TMAAH) having interesting physical properties, is reported as a good source for laser-induced deposition of high-purity aluminium films on GaAs- and Si 3 N 4 -coated GaAs substrates as well as on Al predeposited lines. Thus 30 μm wide, 0.5 μm thick lines, exempt from C, have been deposited using a focused CW visible laser (λ=514 nm), at scanning speeds in the range 2–30μm/s. The laser-induced temperatures, calculated at the centre of the spot, are lower than 300°C. Resistivity measurements performed on Al lines deposited on Si 3 N 4 -coated GaAs substrates give typically 10 μΩ·cm. The very different deposition rates on GaAs or Si 3 N 4 -coated GaAs substrates and on Al predeposited lines, which are observed for the TMAAH complex, are consistent with surface physical chemistry studies, which show that both the surface nature and the chemisorbed species play a leading role in the thermal decomposition of the precursor. Thus, it is demonstrated that a laser-writing technique, based on a surface-controlled pyrolytic process of a well defined precursor can be used for in situ reparation or customization of integrated circuits.

Influence of light irradiation on ZnTe layers grown by MOVPE

Abstract The influence of irradiation on ZnTe layers grown by metalorganic vapor phase epitaxy (MOVPE) is examined in terms of growth rate enhancement, surface morphology, X-ray diffraction patterns and photoluminescence spectra. We observed a growth rate enhancement for illuminated layers using photons with energy over the band gap of ZnTe. On the other hand, the degradation of the surface morphology could be observed even with light intensity as low as 40 mW / cm2 in the visible region. As-grown layers, on GaAs(100) substrates, have been characterised by X-ray diffraction and the photo-assisted deposits were ZnTe single crystals. The crystalline quality of illuminated layers did not appear increased relative to unilluminated epilayers. Eventually, photoluminescence spectra are displayed and revealed the strong influence of light on the intensity of donor—acceptor pair recombinations in comparison to excitonic recombinations. This result may be accounted for by the incorporation of a higher rate of gas phase impurities. This point will be reviewed in the discussion of the possibilities of doping induced by light.