Ge Hydrides Research Articles

Surface studies during growth of Si1−xGex/Si from gaseous Si and Ge hydrides

The epitaxial growth of Si and Si1−xGex alloys from molecular beams of gaseous Si (Si2H6) and Ge (GeH4) hydrides on Si(001) substrates (Si gas-source molecular-beam epitaxy) has been studied using reflection high-energy electron diffraction (RHEED). Diffraction patterns reveal that Ge deposited on Si results in a Stranski–Krastanow growth mode with a change in surface reconstruction prior to the onset of three-dimensional growth. RHEED intensity oscillations measured during Si1−xGex alloy growth indicate that below 600 °C, the addition of GeH4 flux to the substrate results in an enhanced growth rate (GR), but above 600 °C this phenomenon is not observed and the GR remains proportional to the Si2H6 flux. Further, a temperature and flux dependent change in the growth rate, ΔGR, is observed at the Si/Si1−xGex interface. At low temperatures (<580 °C), the growth of several monolayers precedes the establishment of a constant alloy GR, indicative of a graded Ge composition in the interface region. This phenomenon is discussed in terms of the temperature dependent reaction kinetics in this system during growth between 520–640 °C.

Growth rate dependence on GeH 4 during gas source MBE of Si xGe 1- x alloys grown from Si 2H 6 and GeH 4

The epitaxial growth of Si and Si x Ge 1- x alloys from molecular beams of gaseous Si (Si 2H 6) and Ge (GeH 4) hydrides on Si(001) substrates (Si-GSMBE) has been studied using reflection high energy electron diffraction (RHEED). Diffraction patterns reveal that Ge deposited on Si results in a Stranski-Krastanow growth mode with a change in surface reconstruction in the two-dimensional (2D) regime from the two-domain Si(001)-(2×1) to a two-domain Si(2×8)-Ge, prior to the onset of three-dimensional (3D) growth. Using the RHEED intensity oscillation technique during alloy growth it is found that at substrate temperatures below 600°C there is an enhancement in growth rate of the alloy above that of pure Si growth from disilane. This phenomenon has been attributed to the increased desorption rate of hydrogen adatoms due to the presence of Ge, which leads to an acceleration of the heterogenous reaction rate. Consistent with this, during growth at substrate temperatures above the desorption rate maximum for hydrogen, 600°C no enhancement of the growth rate due to the addition of GeH 4 to the beam flux is observed and the growth rate is dependent upon disilane arrival rate. Reaction kinetics are discussed in terms of Ge concentration in the films and the ratio of GeH 4 to Si 2H 6 in the incident beams under various growth conditions.

Surface Reaction Intermediates in Ge Chemical Vapor Deposition on Silicon

AbstractComputational programs are often used for estimating molecular orbital energies and geometries. The results of these calculations can also provide information needed for investigation of adsorption and decomposition mechanisms on surfaces. In this study, ab initio methods are used to calculate properties of gas phase diethylgermane and GeHx-substituted silanes (x=1−3). The silanes are used as models for surface Ge hydrides. The calculated gas phase molecular orbital energies are then compared with experimentally determined molecular orbital energies for the adsorbed species. The surface species are prepared by germane, digermane, ethylbromide, or diethylgermane adsorption on the Si(100)-(2×1) surface and the molecular orbital energies are measured by photoelectron spectroscopy.

All-electron molecular Dirac–Hartree–Fock calculations: Properties of the XH4 and XH2 molecules and the reaction energy XH4→XH2+H2, X=Si, Ge, Sn, Pb

Dirac–Hartree–Fock (DHF) calculations have been carried out on the ground states of the Group IV di- and tetrahydrides. Geometries and infrared data are presented for both sets of molecules, dipole moments for the dihydrides, and the SCF (self-consistent field) reaction energies for the reaction XH4→XH2+H2. The effects of relativity can be seen in shorter bond lengths, higher frequencies for XH4 but lower stretching frequencies for XH2, higher infrared intensities for stretching modes and lower intensities for bending modes, a more positive dipole moment, and decreased stability for XH4 relative to XH2+H2. The results are also compared with relativistic effective core potential (RECP) calculations, first-order perturbation theory (PT) calculations, and with the limited experimental data. PT predicts all properties well for the Ge hydrides, but deviations are noted for the Sn hydrides, which become serious for the Pb hydrides. The full-core RECP calculations generally do not give results as good as PT. The addition of the (n−1)d orbital improves many of the properties. Overall, the quality of the RECPs used is somewhat variable, and no consistent pattern in the deviations from the DHF results is found for the set of RECPs used in this study.

Photoionization mass spectrometric studies of free radicals

Free radicals have been fascinating to chemists for decades, partly because of their important but emphemeral nature as intermediates in chemical reactions, e.g., combustion and atmospheric processes. For example, the reaction OH + CO {yields} H + CO{sub 2} is the dominant source of CO{sub 2} in the oxidation of hydrocarbons and is important in the chemistry of the upper atmosphere and in the formation of chemical smog. This reaction is believed to proceed through a COOH intermediate, but until very recently, this species had not been detected in the gas phase. The depletion of ozone in the stratosphere is attributed to the reaction of the free radical ClO with O{sub 3}. The chemical vapor deposition method of producing solid-state devices based on Si or Ge employs a plasma containing free-radical hydrides of Si and Ge. We have shown that the direct application of eq 1 and 2 to determine the dimerization energy of BH{sub 3} by measuring its ionization potential and its appearance potential from B{sub 2}H{sub 6} is inappropriate for this system. However, a rather lengthy analysis of the data leads to a dimerization energy of 34.3-39.1 kcal/mol, in good agreement with ab initio calculations. Preliminary results frommore » our B{sub 2}H{sub 5} and B{sub 2}H{sub 4} studies indicate that D{sub 0}(B{sub 2}H{sub 5}-H) {le} 102.7 kcal/mol, but D{sub 0}(B{sub 2}H{sub 4}-H) is much weaker, {approx} 40.1 kcal/mol.« less

ChemInform Abstract: Thermolysis and Mass Spectra of Polymeric Germanium Hydride Produced by γ‐Radiolysis.

AbstractUpon heating solid polymeric Ge hydride, obtained by γ‐radiolysis of GeH4, undergoes two successive weight losses at 463 and 1173 K. At 948 K two crystal phases are formed, one of them being pure Ge.

Thermolysis and mass spectra of polymeric germanium hydride produced by γ-radiolysis

TGA, MS and DSC of a solid polymeric Ge hydride, obtained by γ-radiolysis of GeH 4, are reported. Upon heating, it undergoes two successive weight losses at 463 and 1173 K. At 948 K two crystal phases are formed, one of them is pure germanium. Some comparisons with a-Ge: H produced via RF sputtering or glow discharge are reported.

Radiation-chemical hydrogermylation and hydrostannation

1. The hydrostannation and hydrogermylation of olefins is efficiently initiated by60Co γ radiation. 2. The addition of Ge and Sn hydrides to olefins initiated byγ radiation is consistent with the main laws governing radical chain reactions in the liquid phase. 3. The radiation effects in the hydrometallation reaction decrease upon the transition from Sn hydrides to Ge hydrides and from hydrides of the aromatic series to the aliphatic series. 4. The rate of the radiation-chemical hydrometallation increases with increasing electron density in the double bond; the introduction of electron-acceptor substituents lowers the reaction rate.

The preparation of thin layers of Ge and Si by chemical hydrogen plasma transport

It has been proved that the transport of Ge and Si in hydrogen plasma takes place under certain conditions. The transport is probably carried on by volatile hydrides of Ge and Si which are formed during the interaction of hydrogen plasma and the respective semiconductor. The semiconductor layers prepared by this method are compact and well adhesive to the substrate. When deposited on glass they had a polycrystalline structure.