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We present room temperature electroabsorption measurements in a Ge/sub 0.2/Si/sub 0.8/ pin photodiode. The results appear to be very similar to those reported earlier on Ge/sub x/Si/sub 1-x//Si multiple quantum wells. >

Silicon etch rates and the in situ remote H plasma cleaning effectiveness in a Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) system have been measured under conditions of varying substrate temperature, exposure time, and hydrogen pressure. An incubation phenomenon is observed in the Si etch rate as a function of exposure time to the plasma species at a substrate temperature of 250°C. The etch rate is observed to increase from 20 A/hr. for 45 min. exposure to 70 A/hr. for a 4 hour exposure. The dependence of the etch rate on the plasma discharge pressure shows the etch rate to decrease from 72 A/hr. at 50-55 mTorr to 4 A/hr. for pressures greater than 125 mTorr. The substrate temperature is found to have the greatest effect on both the cleaning of the surface and the Si etch rate, with 250AC resulting in a surface with oxygen and carbon concentrations less than the detection limit for Auger Electron Spectroscopy. On wafers exposed to atomic H at both 150 and 400AC, oxygen, carbon and nitrogen were detected after 4 hr. exposures. The etch rate is inversely related to temperature, consistent with earlier results. At a substrate temperature of 150AC, Reflection High Energy Electron Diffraction (RHEED) shows the diffraction pattern to change from a streak pattern observed at higher temperatures to a spot pattern, indicating a roughened surface after 4 hrs. of etching. Wafers cleaned at temperatures above 150AC yielded streak patterns even after 4 hr. exposure. Increasing the H pressure during the clean had no effect on the final RHEED pattern.

The use of an aqueous HF dip as the final ex situ cleaning step following a modified RCA clean before growth of epitaxial Si layers by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) has been found to cause haze. Two approaches have been employed to eliminate the haze: addition of alcohol to lower the surface energy of the HF solution, and the application of the HF solution by a spin etch technique. We have studied final ex situ treatments with water/HF, ethanol/HF and methanol/HF solutions applied by both dip and by spin methods, and their effects on haze in low temperature Si homoepitaxy by RPCVD. The ratios of solvent to 49% HF (aq) were 40:1, 10:1 and 5:1. Surface carbon and oxygen levels, as measured by Auger Electron Spectroscopy (AES) after the HF solution treatments were found to be comparable for the alcohol/HF and water/HF dips. For the spin application, methanol/HF resulted in higher surface carbon coverage than for ethanol or water HF solutions. Epitaxial silicon films, 2000–4000A thick, were grown on the wafers at 450°C using RPCVD. Secondary Ion Mass Spectroscopy (SIMS) measurements showed elevated levels of oxygen and carbon contamination at the epi-substrate interface to result when the wafers were treated with water/HF solutions rather than alcohol/HF, but no advantage was observed for the spin versus the dip technique. Films which were cleaned by water/HF exhibited patterns of haze over the wafer surface showing flow lines where the liquid drained from the surface for both dip and spin applications. The alcohol/HF solutions resulted in substantial reduction in haze for the dip application and elimination of haze for the spin application.

Atomic layer epitaxy (ALE) of Si has been demonstrated by using remote He plasma low energy ion bombardment to desorb H from an H-passivated Si(100) surface at low temperaturea and subsequently chemisorbing Si 2 H 6 on the surface in a self-limiting fashion. Si substrates were prepared using an RCA clean followed by a dilute HF dip to provide a clean, dihydride-terminated (1 × 1) surface, and were loaded into a remote plasma chemical vapor deposition system in which the substrate is downstream from an r.f. noble gas (He or Ar) glow discharge in order to minimize plasma damage. An in situ remote H plasma clean at 250°C for 45 min was used to remove surface O and C and to provide an alternating monohydride and dihydride termination, as evidenced by a (3 × 1) reflection high energy electron diffraction (RHEED) pattern. It was found necessary to desorb the H from the Si surface to create adsorption sites for Si- bearing species such as Si 2 H 6 . Remote He plasma bombardment for 1–3 min was investigated over a range of temperature (250°C−410°C), pressures (50–400 mTorr) and r.f. powers (6–30 W) in order to desorb the H and to convert the (3 × 1) RHEED pattern to a (2 × 1) pattern which is characteristic of either a monohydride termination or a bare Si surface. It was found that as He pressures and r.f. powers are raised the plasma potential and mean free paths are reduced, leading to lower He bombardment energies but higher fluxes. Optimal He bombardment parameters were determined to be 30 W at 100 mTorr process pressure at 400°C for 1–3 min. He was found to be more effective than Ar bombardment because of the closer match of the He and H masses compared with that between Ar and H. Monte Carlo TRIM simulations of He and Ar bombardment of H-terminated Si surfaces were performed 3o validate this hypothesis and to predict that approximately 3 surface H atoms were displaced by the incident He atoms, with no bulk Si atom displacement for He energies in the range 15–60 eV. The He bombardment cycles were followed by Si 2 H 6 dosing over a range of partial pressures (from 10 −7 Torr to 1.67 mTorr), temperatures (250°C–400°C) and times (from 20s to 3 min) without plasma excitation, because it is believed that Si 2 H 6 can chemisorb in a self-limiting fashion on a bare Si surface as two silyl (SiH 3 ) species, presumably leading to a H-terminated surface once again. The Si 2 H 6 dosing pressures and times corresponded to saturation dosing (about 10 6 langmuirs). Alternate Si 2 H 6 dosing and He low energy ion bombardment cycles (about 100–200) were performed to confirm the ALE mode of growth. It was found that the growth per cycle saturates with long Si 2 H 6 dosing at a level which increases slightly with He bombardment time. At 400°C, for 2 min He bombardment at 100 mTorr and 30 W, the growth per cycle saturates at about 0.1 monolayers cycle −1 , while for 3 min He bombardment the Si growth saturates at about 0.15 monolayers cycle −1 . It was also confirmed that the growth is achieved only by using alternate He bombardment and Si 2 H 6 dosing. He bombardment alone for a comparable time (3 min × 100 cycles) causes a negligible change in the Si film thickness (less than 5 A). Similarly, thermal growth using Si 2 H 6 under these conditions for (3 min × 100 cycles) causes negligible deposition (less than 5 A).

GexSi1−x/Si heteroepitaxial thin films have been grown using the low‐temperature remote plasma‐enhanced chemical vapor deposition (RPCVD) approach, in which the substrate is kept remote from the glow discharge, and an Ar plasma is employed to indirectly activate the reactant gases (SiH4 and GeH4) and drive the chemical deposition reactions. Secondary ion mass spectroscopy (SIMS), plan‐view and cross‐sectional transmission electron microscopy (TEM), and in situ reflection high‐energy electron diffraction (RHEED) have been employed to analyze the films with different Ge mole fractions and thicknesses. Abrupt Si/GexSi1−x heterointerfaces with the Ge concentration changing by 10× in about 30 A (SIMS resolution limit) have been achieved. Commensurate growth has been observed for layers whose thicknesses are below the critical layer thicknesses (CLTs). Crystalline GexSi1−x/Si films with high mole fractions of Ge (up to 60%), which are thicker than the CLTs, show relaxation of misfit strain. This results in more...

In situ boron doping of Si epitaxial films grown at 450‡ C by remote plasma-enhanced chemical vapor deposition (RPCVD) has been studied using secondary ion mass spectroscopy (SIMS), Hall effect measurements, defect etching in conjunction with Nomarski microscopy, cross-sectional transmission electron microscopy (XTEM), and current-voltage measurements. Boron incorporation is shown to be controllable and electrically active from 7 × 1017 to over 1020 cm-3, with no dependence on process parameters (temperature, rf power, and substrate bias) in the ranges studied, other than the B2H6/SiH4 gas-phase ratio. No change in deposition rate upon introduction of B2H6 dopant gas is seen, contrary to what has been observed in several higher-temperature CVD processes. No defects such as stacking faults are seen under Nomarski microscopy, but a visible haze covers some areas ofin situ B-doped wafers. This haze appears to consist of amorphous cone-shaped structures with their apexes at the substrate-epilayer interface. The origin of the conical defects is believed to be related to some phenomenon at the initiation of growth. In order to evaluate the electrical quality ofin situ B-doped epilayers,P +/N mesa diodes have been fabricated using both homoepitaxial and heteroepitaxial (GexSi1-x)p-type epitaxial films. The electrical junction in these diodes coincides with the (epi-substrate)—interface in the grown films. To avoid interdiffusion or annealing effects during diode fabrication, all processing temperatures were kept at or below 450‡ C. Ideality factors are 1.2-1.3 for all diodes, indicating diffusion-limited transport rather than recombination in the depletion region.

In this work, remote plasma-enhanced chemical vapor deposition (RPCVD) has been used to grow GexSi1−x/Si layers on Si(100) substrates at 450° C. The RPCVD technique, unlike conventional plasma CVD, uses an Ar (or He) plasma remote from the substrate to indirectly excite the reactant gases (SiH4 and GeH4) and drive the chemical deposition reactions. In situ reflection high energy electron diffraction, selected area diffraction, and plan-view and cross-sectional transmission electron microscopy (XTEM) were used to confirm the single crystallinity of these heterostructures, and secondary ion mass spectroscopy was used to verify abrupt transitions in the Ge profile. XTEM shows very uniform layer thicknesses in the quantum well structures, suggesting a Frank/ van der Merwe 2-D growth mechanism. The layers were found to be devoid of extended crystal defects such as misfit dislocations, dislocation loops, and stacking faults, within the TEM detection limits (∼105 dislocations/cm2). GexSi1−x/Si epitaxial films with various Ge mole fractions were grown, where the Ge contentx is linearly dependent on the GeH4 partial pressure in the gas phase for at leastx = 0 − 0.3. The incorporation rate of Ge from the gas phase was observed to be slightly higher than that of Si (1.3:1).

Remote plasma-enhanced chemical vapor deposition (RPCVD) is a low temperature growth technique which has been successfully employed inin situ remote hydrogen plasma clean of Si(100) surfaces, silicon homoepitaxy and Si1- xGex heteroepitaxy in the temperature range of 150–450° C. The epitaxial process employs anex situ wet chemical clean, anin situ remote hydrogen plasma clean, followed by a remote argon plasma dissociation of silane and germane to generate the precursors for epitaxial growth. Boron doping concentrations as high as 1021 cm−3 have been achieved in the low temperature epitaxial films by introducing B2H6/He during the growth. The growth rate of epitaxial Si can be varied from 0.4A/min to 50A/min by controlling therf power. The wide range of controllable growth rates makes RPCVD an excellent tool for applications ranging from superlattice structures to more conventional Si epitaxy. Auger electron spectroscopy analysis has been employed to confirm the efficacy of this remote hydrogen plasma clean in terms of removing surface contaminants. Reflection high energy electron diffraction and transmission electron microscopy have been utilized to investigate the surface structure in terms of crystallinity and defect generation. Epitaxial Si and Si1-xGex films have been grown by RPCVD with defect densities below the detection limits of TEM (~105 cm-2 or less). The RPCVD process also exploits the hydrogen passivation effect at temperatures below 500° C to minimize the adsorption of C and 0 during growth. Epitaxial Si and Si1-xGex films with low oxygen content (~3 × 1018 cm-3) have been achieved by RPCVD. Silicon and Si/Si1-xGex mesa diodes with boron concentrations ranging from 1017 to 1019 cm-3 in the epitaxial films grown by RPCVD show reasonably good current-voltage characteristics with ideality factors of 1.2-1.3. A Si/Si1-xGex superlattice structure with sharp Ge transitions has been demonstrated by exploiting the low temperature capability of RPCVD.In situ plasma diagnostics using single and double Langmuir probes has been performed to reveal the nature of the RPCVD process.

Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) is a low temperature growth technique which has: been successfully employed tor in situ remote hydrogen plasma cleaning, dielectric deposition, silicon homoepitaxy and Si1−x, Gex heteroepitaxy in the temperature range of 150°C-450°C. The growth rate of epitaxial Si in the RPCVD process can be varied from 0.4A/min to 50A/min by controlling the r-f power. The wide range of controllable growth rates makes RPCVD a excellent tool for applications ranging from quantum-well type structures to more conventional Si epitaxy. Epitaxial Si and Si1−x, Gex films with defect densities below the detectable limits of TEM (∼105 cm− 2 or less) and low oxygen content (∼3×101B cm− 3) have been achieved by RPCVD. The in situ boron-doped Si films have been grown on n-typo, phosphorus-doped substrates to form p-n junctions for mesa diode fabrication. The mesa diodes with different boron doping concentrations (1017-1019 cm− 3) show good current-voltage characterist...

Single‐crystal GexSi1−x/Si superlattices have been successfully fabricated using remote plasma‐enhanced chemical vapor deposition, a novel low‐temperature thin‐film growth technique. Reflection high‐energy electron diffraction, cross‐sectional transmission electron microscopy (XTEM), plan view TEM, x‐ray‐diffraction, and secondary‐ion mass spectroscopy techniques have been applied to study the crystallographic properties of the superlattice structures. Arrays of dislocation lines, which are either parallel or perpendicular to each other, have been observed in the superlattices for those cases in which the total layer thickness exceeds the critical layer thickness. The location, orientation, and Burgers vectors of the misfit dislocation lines have been analyzed. Possible mechanisms of the generation of the misfit dislocations are also discussed.

We have used photocurrent measurements to demonstrate a strong electroabsorption effect in GexSi1−x/Si multiple quantum wells grown by remote plasma‐enhanced chemical vapor deposition. Large voltage‐induced shifts in absorption are observed at room temperature in the wavelength range from 1.2 to 1.58 μm. We anticipate that the results can be extended to fabricate GexSi1−x optoelectronic devices operating at room temperature.

Hydrogen desorption from (2×1) and (3×1) H‐terminated Si(100) surfaces due to irradiation by electron beams with 2–5 keV beam energies has been investigated both experimentally and theoretically. Auger electron spectroscopy (AES) has been employed to monitor Si, O, and C signals periodically with continuous irradiation of an electron beam on H‐terminated Si(100) surfaces. An incubation phenomenon is observed in the time evolution profiles of the Si, O, and C AES signals for all H‐terminated Si(100) surfaces. The incubation period is believed to be associated with the time required for desorption of hydrogen from the H‐terminated Si surface as a result of electron beam irradiation. Among (2×1) and (3×1) H‐terminated Si(100) surfaces, the (3×1) surface is found to have greater hydrogen coverage than (2×1) surface. The hydrogen desorption cross section is found to range from 4×10−19 to 8×10−18 cm2 and decrease with increasing beam energy in the 2–5 keV range.

The role of silicon hydride species in the photoluminescence intensity behavior of porous Si has been studied. The surfaces of luminescent porous Si samples were converted to a predominate SiH termination using a remote H plasma. The as‐passivated samples were then immersed in various concentrations of hydrofluouric solutions to regulate the recovery of SiH2 termination on the surface. Photoluminescence measurements and transmission Fourier‐transform infrared spectroscopy have shown that predominant silicon monohydride (SiH) termination results in weak photoluminescence. In contrast, it has been observed that the appearance of silicon dihydride (SiH2) coincides with an increase in the photoluminescence intensity.

The ability to deposit boron-doped homoepitaxial silicon films at very low temperatures (450°C) using remote plasma-enhanced chemical vapor deposition (RPCVD) has been investigated. The boron incorporation efficiency is found to be between 0.2 and 0.4. 100% electrical activation is obtained for an epitaxial silicon film with boron doping of 1 x 10 19 cm −3 deposited at 450°C. The current-voltage characteristics for mesa diodes fabricated on these in situ boron-doped films where the maximum temperature during the entire fabrication process was kept below 450°C indicate an ideality factor of 1.2 and reverse bias leakage current of 320 nA cm −2 . Addition of diborane is found to result in the genaration of defects which require increased deposition temperatures compared with undoped films to maintain excellent crystalline quality.

Low‐temperature growth processes are needed in order to fully exploit the potential of GexSi1−x/Si heterostructures. Remote plasma‐enhanced chemical vapor deposition has been successful for silicon homoepitaxy at substrate temperatures as low as 150 °C. We report the growth of GexSi1−x/Si heterostructures with values of x between 0.07 and 0.73, and at substrate temperatures of 305 and 450 °C. The films grown at 450 °C have excellent crystallinity, low defect densities, and very abrupt interfaces, while films grown at 305 °C have degraded crystallinity.

Low temperature Si and Si1−xGex epitaxy is one of the major thrusts in the trend towards low temperature Si processing for future generation ULSI circuits and novel Si-based devices. A remote plasma-enhanced chemical vapor deposition (RPCVD) technique has been developed to achieve Si homoepitaxy and Si1−xGex heteroepitaxy at low temperatures (≤450'C). P-type films have been grown by introducing 90 ppm or 5000 ppm B2H6/He into the system during the growth process to achieve in situ electrically active boron doping. A mesa diode structure with minimal thermal budget in the fabrication process has been employed to evaluate the properties of the boron-doped Si and Si1−xGex films grown at 450°C by RPCVD. Leakage current densities are reduced for diodes grown at 14–18 W (40–50 Å/min. growth rates) compared to similar devices grown at 6.6 W (5 Å/min.). N-type films have been grown by the introduction of 50 ppm PH3/He. Secondary ion mass spectroscopy (SIMS) has been employed to analyze the boron and phosphorus incorporation efficiencies and doping profiles under different conditions. Boron and phosphorus doping profile transitions as sharp as 50–100 Å/decade have been achieved. Transmission electron microscopy (TEM) has been used to investigate the microstructure of the B-doped films.

We have studied the conditions for effective removal of H from the silicon (100) surface by Ar and He plasma bombardment as a function of pressure, plasma power and time. At a given pressure, a range of rf plasma powers exists for effective H-desorption. For example, at 250°C and for 100 mTorr of He, H is desorbed only between 12 and 50W of plasma power. The range of effective powers was found to become narrower with increasing pressure. We have also found the efficacy of the H-plasma clean to be reduced by addition of He and Ar. Substrate damage results from Ar addition and from increased plasma power for pure H. The results are discussed along with Langmuir probe analysis of the various plasma conditions.

Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) has been successfully used to grow GexSi1−x/Si (x = 0.1 – 1.0) heteroepitaxial structures at low temperatures (∼450°C). This technique utilizes a noble gas (Ar or He) r-f plasma to decompose reactant gases (SiH4 and GeH4) and drive the chemical deposition reactions in the gas phase as well as on the substrate surface. Growth of pure Ge on Si is of great interest because it provides a promising technique for making suitable low-cost substrates for thin-film Ge photodetectors as well as GaAs devices on Si substrates. The realization of these applications depends on the ability to grow high-quality epitaxial Ge layers on Si substrates. Since GaAs is lattice matched to Ge, growth of Ge layers on Si substrates with good crystalline perfection would permit the integration of GaAs and Si devices. Islanding was observed after the growth of pure Ge films directly on Si(100) for a wide range of plasma powers (7W ∼ 16W) in RPCVD. Cross-sectional TEM analysis showed that the islands have complicated facet structures, including {311} planes. Graded Gex Si1−x buffer layers with different Ge profiles have been used prior to the growth of Ge. It was found that uniform Ge films can be obtained using a buffer with an abrupt Ge profile, and the dislocation density in the Ge film decreases with increasing distance from the substrate.

Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD), which involves nonthermal, remote plasma excitation of precursors, has been demonstrated to be a novel and attractive technique for low temperature (150-450C) Si and Sil-xGex epitaxy for applications in Si ULSI and novel Si heterostructure devices which require compact doping profiles and/or heterointerfaces. An in situ low temperature remote hydrogen plasma clean in the Ultra-High Vacuum (UHV) deposition chamber in order to achieve a chemically passive, hydrogenated Si surface with minimal O, C and N contamination, is a critical component of the process. The ex situ wet chemical cleaning consists of ultrasonic degreasing and a modified RCA clean, followed by a final dilute HF dip. The in situ clean is achieved by remote plasma excited H, where H introduced through the plasma column is r-f excited such that the plasma glow does not engulf the wafer. In situ AES analysis shows that the remote H plasma clean results in very substantial reduction of the C, O and N contamination on the Si surface. We believe that the H plasma produces atomic H which, in turn, produces a reducing environment and has a slight etching effect on Si and SiO2 by converting them to volatile byproducts. TEM analysis of the wafers subjected to this clean indicate that defect-free surfaces with dislocation loop densities below TEM detection limits of 105 /cm2 are achievable. Corroborating evidence of achieving an atomically clean, smooth Si surface by remote H plasma clean as obtained from in situ RHEED analysis will also be presented. After in situ H cleaning at low pressures (45 mTorr), typically for 30 min. at a substrate temperature of 310 C, we observe both stronger integral order streaks compared to the as-loaded sample and the appearance of less intense half-order lines indicative of a (2 × 1) reconstruction pattern, indicating a monohydride termination. A (3 × 1) reconstruction pattern is observed upon H plasma clean at lower temperatures (250 C), which can be attributed to an alternating monohydride and dihydride termination. Results of air exposure of hydrogenated Si surfaces by AES analysis indicate that the (3 × l) termination is chemically more inert towards readsorption of C and 0. Successful Si homoepitaxy and Si/Sil-xGex heteroepitaxy under a variety of surface cleaning conditions prove that by a combination of these cleaning techniques, and by exploiting the inertness of the H-passivated Si surface, very low defect density films with 0 and C levels as low as 1X1018 cm−3 and 5×1017 cm−3, respectively, can be achieved.

The density of misfit dislocations in GexSi1−x films has been measured as a function of deposition temperature and r-f plasma power in Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD). The misfit dislocation density decreases as the deposition temperature is lowered from 450°C to 410°C. As the plasma power is increased from 6.6 to 16W, the dislocation density peaks at lOW and then decreases with increasing power.

Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) has been used to grow GexSi1−x/Si heteroepitaxial thin films at low temperatures (∼450°C). In situ RHEED has been used to confirm that smooth, single crystal heteroepitaxial films can be grown by RPCVD. Plan-view and cross-sectional TEM have been employed to study the microstructure of the heteroepitaxial films. Lattice imaging high resolution TEM (HRTEM) has shown perfect epitaxial lattice alignment at the heterojunction interfaces. GexSi1−x/Si films which exceed their CLT's appreciably show dense Moiré fringes under plan-view TEM. The spacings between the fringes have been used to estimate the relaxed lattice constants. In addition to the inhomogeneous strain observed in-XTEM, Selected Area electron Diffraction (SAD) analysis of the interfaces displays two split patterns. The spacings between the diffraction spots have been used to calculate the lattice constants in the epitaxial films in different crystal directions, which agree very well with the prediction by Vegard's law as well as the estimate from plan-view TEM analysis. HRTEM analysis also reveals the crystallographic nature of the interfacial misfit dislocations in the relaxed films.

Low temperature heteroepitaxial growth of Si1−xGex films with mole fractions “x” ranging from 0.07 to 0.72 on Si(100) has been achieved by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) at substrate temperatures of 305°C and 450°C. Reflection High Energy Electron Diffraction (RHEED), Transmission Electron Microscopy (TEM), and Secondary Ion Mass Spectroscopy (SIMS) were employed to characterize the crystallinity, composition and interfacial sharpness. The Si1−xGex films with thickness below the critical layer thickness were confirmed to have excellent crystallinity with defect density below the sensitivity of TEM analysis (105 cm−2). The Ge profile, from SIMS analysis, in a Si/Si0.8Ge0.2/Si/Si0.82Ge0.18 multilayer structure was found to have a transition width of 30Å/decade, which is the resolution limit of SIMS analysis. There is no Ge segregation observed at the Si/Si1−xGex interface. A superlattice structure with 24 pairs of Si(60Å)/Si0.8Ge0.2 (60Å) layers has been successfully grown by RPCVD at 450°C. From cross-sectional TEM analysis, very low defect densities and abrupt Ge transitions were confirmed.

The addition of germane and dopant gases significantly alter the growth kinetics of low temperature Si epitaxy. Germane, phosphine, and diborane have been reported to both enhance and retard film growth rate in various processes. The growth kinetics of remote plasma enhanced chemical vapor deposition are largely unaffected by the addition of GeH4 or by in situ doping. Adsorption sites are created by low energy ion bombardment and are only minimally dependent on temperature for activation. Ion‐induced gas phase reactions also play an important role in the deposition via formation of precursors which have greater sticking probabilities and insertion rates into the hydrogenated surface than for the direct reactions of SiH4 and GeH4 with the Si surface in thermal chemical vapor deposition.