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Chemical Vapor Deposition delivers an atomic element into a solid phase via a gas phase. In such context, knowledge of the vapor – solid distribution of the elements is key. But CVD is a notorious non-equilibrium process. Notwithstanding the non-equilibrium, an analysis of silicon germanium chemical vapor deposition, via silane and germane, is conducted with classical thermodynamics for a complete determination of the vapor – solid distribution. And a theory assuming a heterogeneous chemical equilibrium is developed. The knowledge of two linear functions is enough for accessing a distribution which is then determined over the full range of composition, without any major difficulty. Reduced pressure chemical vapor deposition and ultra-high vacuum chemical vapor deposition vapor – solid distributions are also reconciled within the same conceptual framework. The impact of the pressure, and of silicon precursors are neatly clarified. The underlying laws necessary for the determination of Si1-xGex vapor - solid distributions are thus completely known. VS distributions of binary alloys such as Si:B, Si:P and Ge1-xSnx, are also inferred to experience similar chemical equilibria.

We have studied the very low temperature epitaxy of pure Ge and of Ge-rich SiGe alloys in a 200 mm industrial reduced pressure chemical vapour deposition tool. We have, first of all, benchmarked germane (GeH 4 ) and digermane (Ge 2 H 6 ) for the growth of pure Ge. Used Ge 2 H 6 instead of GeH 4 enabled us to dramatically increase the Ge growth rate at temperatures 425 °C and lower (5.6 nm min −1 compared to 0.14 nm min −1 at 350 °C with a Ge 2 H 6 mass-flow one fourth that of GeH 4 ). We have also evaluated at 400 °C, 100 Torr, the impact of the GeH 4 or Ge 2 H 6 mass-flow on the Ge growth rate. For a given Ge atomic flow, the higher surface reactivity of digermane yielded roughly five times higher growth rates than with germane. We have then combined digermane with disilane (Si 2 H 6 ) or dichlorosilane (SiH 2 Cl 2 ) in order to study the GeSi growth kinetics at 475 °C, 100 Torr. While the SiH 2 Cl 2 mass-flow did not have any clear influence on the GeSi growth rate (with a 14 nm min −1 mean value, then), a Si 2 H 6 mass-flow increase resulted in a slight GeSi growth rate increase (from 11 nm min −1 up to 14 nm min −1 ). Significantly higher Ge concentrations were otherwise accessed with dichlorosilane than with disilane, in the 77–82% range compared to the 39–53% range, respectively.

In the present work homoepitaxial Ge layers were deposited by means of metal organic vapor phase epitaxy (MOVPE) on Ge using iso-butyl germane (iBuGe) as a metal organic precursor. Layers of different thicknesses were grown by varying the deposition temperature between 550 and 700 °C on n- and p-type Ge substrates. The films were found to be intrinsically p-type with high carrier concentration, but using AsH3 it was possible to achieve n-type doping. TEM and X-ray diffraction were used to assess the good crystallographic quality of the layers. By depositing a p-type layer onto an n-type Ge substrate or, vice versa, an n-type layer on a p-type Ge substrate is was possible to realize p/n (or n/p) junctions. Mesa structures were realized in order to perform electrical characterizations of the junctions.

In situ control over the growth morphology of nanocones has important implications to their application in photovoltaic and thermoelectric devices. In this study, Ge nanocones were grown by an Au-catalyzed process in a chemical vapor deposition (CVD) chamber using germane (GeH 4 ) as the source gas. The growth temperature was varied for different segments of the growth, and a corresponding variation of taper (angle of cone sidewalls relative to the axial direction) in the segments was observed. The structures obtained in these experiments reveal their temperature-dependent modes of growth. When the growth was conducted at an initial temperature of 350 °C then increased to 400 °C, faceted pillars consisting of a base segment of largely uniform diameter and a conical tapered tip were formed. When the growth was conducted at 395 and 375 °C, then at 350 °C, the nanocones featured a base with a wider taper and tips with a smaller taper. The dependence on temperature of the growth morphology is attributed to the relative influence of competing growth mechanisms at different temperature regimes: catalyzed unidirectional growth at lower temperatures approaching the Au–Ge eutectic point, and increasingly isotropic and facet-bounded epitaxial growth at higher temperatures up to 400 °C. The multi-step growth method also provides a reliable method of determining the rate and mode of catalyzed growth.

Epitaxial growth of germanium is attractive for Ge/III–V hetero devices such as multi-junction solar cells. We investigated the growth of Ge with iso-butyl germane (IBGe) as germanium source and found a strong memory effect in our AIX2600-G3 metalorganic vapor phase epitaxy (MOVPE) reactor. The germanium background led to a higher n-type doping of i-GaAs and strongly reduced the photoluminescence (PL) intensity of Al 0.3 Ga 0.7 As and Ga 0.5 In 0.5 P. With secondary ion mass spectroscopy (SIMS) the quantity of Ge in Al 0.3 Ga 0.7 As could be determined to be in the range of 2×10 17 cm −3 , whereas a Ge-atom concentration in Ga 0.5 In 0.5 P of up to 2×10 18 cm −3 was measured. The memory effect could be eliminated by changing all contaminated parts inside the MOVPE reactor.

Commercial strategy to graded SiGe buffer layers and “strained silicon” involves passing germane (GeH 4 ) gas or germanium tetrachloride (GeCl 4 ) vapors as the preferred germanium sources, along with a silicon source over a heated substrate. Today, one of the major limitations impacting the commercialization of SiGe technology is the lack of a commercially viable and safer process that eliminates hazards associated with GeH 4 and the excessively higher thermal budget associated with GeCl 4 . The key to growing successful SiGe structures is thus a strategic deposition process that employs safer alternative germanium sources, and allows a wide growth temperature window without degrading the film properties and jeopardizing the environment, health and safety (EHS) aspects of overall operation. In this paper, we report on the development of safer alternative liquid germanium precursors along with the first successful use of a new organo germanium precursor, iso-butyl germane (IBGe) for the growth of high purity Ge and SiGe films. We also detail our strategy to identify the most appropriate candidates from a large number of organo germanium compounds along with initial results on SiGe films and high-quality epitaxial Ge films deposited using IBGe.

Using a reduced-pressure chemical vapor deposition cluster tool, we have studied at a growth pressure of 20 Torr, the growth kinetics of Si and SiGe on Si(1 0 0), Si(1 1 0) and Si(1 1 1) substrates. The Si growth rates on Si(1 1 0) and Si(1 1 1) are consistently less than the ones on Si(1 0 0), this both in the high temperature, supply-limited regime and especially in the low-temperature, H-desorption-limited one. We have also studied at 700 °C the growth kinetics of SiGe using a dichlorosilane+germane chemistry. For a given set of precursor mass-flows, the Ge concentration decreases significantly when switching from a (1 0 0) to a (1 1 1) and finally to a (1 1 0) surface. The SiGe growth rate increases almost linearly with the GeH 4 mass-flow on (1 0 0) surfaces. By contrast, it bows downwards from linearity on (1 1 0) and (1 1 1) surfaces, leading for high germane mass-flows to lower growth rates than on (1 0 0).

Germanium and gallium arsenide have long been used in semiconductor structures and electronic devices. While organometallic vapor phase epitaxy (OMVPE) of gallium arsenide on germanium substrate is quite common in the solar cell industry for satellite panels, the OMVPE of germanium is still relatively uncommon. We report on the development and first use of the new organogermanium precursor, iso-butyl germane, [C 4 H 7 ]GeH 3 , and its use for the growth of high-purity germanium films. We report how we identified useful OMVPE precursors from a larger number of compounds that were synthesized from classes of organogermanium hydrides and organogermanium halides. Finally, we report initial results on high-quality epitaxial Ge films.

Gas source molecular beam epitaxy is used for the growth of SiGeC layers from disilane, germane and methylsilane precursors at low substrate temperatures. A systematic method of carbon concentration determination based on a combination of X-ray diffraction and X-ray reflectivity is examined. The grown layers were annealed using rapid thermal annealing and analysed with X-ray diffraction, X-ray reflectivity and secondary ion mass spectrometry. The recovery of compressive strain in the SiGeC layer is correlated to the loss of carbon through diffusion and indicates that the carbon atoms are incorporated substitutionally in the as-grown layers.

We have studied, at 20 Torr, the high-temperature growth kinetics of SiGe using a dichlorosilane+germane+hydrochloric acid chemistry. Adding HCl leads at 850 °C to a slight increase in the germanium content x of SiGe layers. Its dependence on the F(GeH 4 )/F(SiH 2 Cl 2 ) mass flow ratio is well accounted for by a x / ( 1 - x ) = m ( F ( GeH 4 ) / F ( SiH 2 Cl 2 ) relationship, with m increasing from 2.41 (no HCl) to 2.77 (F(HCl)/F(H 2 )=0.00833). The SiGe growth rate increases slightly, and then stabilizes as the GeH 4 flow increases. This is attributed for low GeH 4 flows to an increased hydrogen desorption caused by the presence of Ge atoms on the growing surface that frees nucleation sites for the incoming Ge and Si atoms. For high GeH 4 flows, we are at 850 °C in a supply-limited regime, where the growth rate is limited by the amount of gaseous precursors on the growing surface. Adding some HCl leads at 850 °C to a strong decrease of the SiGe growth rate. The influence of the growth temperature between 750 and 950 °C on the SiGe growth kinetics can schematically be described as follows: (i) The Ge concentration decreases for given amounts of SiH 2 Cl 2 and GeH 4 as the growth temperature increases (at least for Ge contents ⩽25%), which is reflected by an m parameter value decreasing from 2.43 (800 °C) to 1.71 (950 °C). (ii) The SiGe growth rate increases as the GeH 4 and/or the growth temperature increases; for high GeH 4 flows and/or high temperatures we are in a supply-limited regime, whereas for low GeH 4 flows and/or low temperatures we are in a surface hydrogen–desorption-limited regime. Playing with the absolute values of the SiH 2 Cl 2 and GeH 4 flows (in order to have access to both low and high F(GeH 4 )/F(SiH 2 Cl 2 )+F(GeH 4 ) mass flow ratios) and the growth temperature, we have been able to gain access to a very large Ge concentration range, between 2% and 50%.

We have investigated the structural properties of Ge thick films grown directly onto Si(0 0 1) substrates using a production-compatible reduced pressure-chemical vapor deposition system. The thick Ge layers grown using germane and a low-temperature/high-temperature approach are in a definite tensile-strain configuration. The threading dislocation density is as low as 6×10 6 cm −2 for 2.5 μm-thick layers that have subsequently been submitted to a 8 times {750 °C, 10 min/900 °C, 10 min} cyclic anneal under H 2 . The surface of those Ge thick layers is rather smooth, especially when considering the large lattice mismatch in-between Ge and Si. The root mean square roughness is indeed of the order of 1 nm only for 2.5 μm thick Ge layers. Some out-diffusion of Si towards the surface of the Ge layer has also been evidenced, with diffusion coefficients slightly higher than those of pre-implanted Si inside bulk Ge. Finally, we have studied the in situ n- and p-type doping of Ge. A B ions concentration as high as 1×10 20 cm −3 has been achieved at 400 °C inside Ge using diborane as a gaseous precursor. Meanwhile, the P ions concentration at 850 °C fluctuates in-between 1×10 17 and 4×10 17 cm −3 more or less independently of the phosphine flow. This is most probably due to some significant surface segregation of P.

The aim of this study being the selective epitaxial growth of either intrinsic or in situ doped raised sources and drains, we have studied the growth kinetics and the boron and phosphorus doping of Si and SiGe with a dichlorosilane+germane+hydrochloric acid chemistry. Adding HCl to SiH 2 Cl 2 +GeH 4 leads at the same time to a strong decrease of the Si or SiGe growth rate and to a significant increase in the germanium content of the layers. Switching from bulk to SOI substrates with a very thin Si top layer induces a significant decrease in the Si growth rate, which we have quantified as a function of the buried oxide thickness. As far as the doping at 800°C of Si layers grown with a SiH 2 Cl 2 +HCl chemistry is concerned, we have obtained a peak for B ions at 1.3×10 20 cm −3 . Beyond this peak, poly-crystalline Si:B layers are formed. Meanwhile, the phosphorus ion concentration in Si increases monotonously with the PH 3 flow, reaching a maximum value equal to 1.3×10 19 cm −3 . Switching over to Si 0.8 Ge 0.2 (grown at 700°C with a chlorinated chemistry) enables to drastically reduce the resistivity (minima: 9.75×10 −4 Ω cm for SiGe:P and 1.02×10 −3 Ω cm for SiGe:B) and thus meet, for a lower thermal budget, the requirements of the forthcoming 45 nm gate length technology node (not reached for Si:P). Finally, as far as growth kinetics are concerned, carrying out some heavy boron (phosphorus) doping induces a strong increase (decrease) of the Si or SiGe growth rate and a reduction (strong increase) of the apparent Ge concentration.

We have studied in reduced pressure chemical vapor deposition the selective epitaxial growth (SEG) of Si and SiGe using a dichlorosilane+germane+hydrochloric acid chemistry. We have first of all highlighted the specifics of the SEG of Si on patterned wafers with a dichlorosilane+hydrochloric acid chemistry. We have then dealt with the SEG of SiGe, focusing notably on the so-called loading effects (increase of the SiGe growth rate and of the Ge concentration when switching over from a blanket to a dielectric-masked substrate). Finally, we have studied the thermal stability of typical Si/SiGe/Si stacks versus conventional anneals used nowadays for advanced devices in the microelectronics industry. All this knowledge can be used to selectively grow Si or Si/SiGe/Si stacks inside the Si windows of patterned wafers for the formation of raised sources and drains or for the channel engineering of p-type metal oxide semiconductor transistors.

We have studied the growth kinetics of Si and SiGe using a dichlorosilane+germane+hydrochloric acid chemistry. Adding HCl to SiH 2 Cl 2 leads to a slight decrease of the Si growth rate at high temperature (same activation energies E a =4 kcal mol −1 with or without HCl, however). A more consequent drop occurs in the low-temperature region, where the Si growth rate is limited by the desorption of the Cl atoms (instead of the H atoms) from the growing surface ( E a =87 ⇔ 48 kcal mol −1 ). Adding HCl leads at 750°C to a significant increase in the germanium content x of SiGe layers. Adopting a x 2 /(1− x )= n ( F (GeH 4 )/ F (SiH 2 Cl 2 )) dependence of x on the F (GeH 4 )/ F (SiH 2 Cl 2 ) mass flow ratio, this translates into a n value linearly increasing with the HCl mass flow from n =0.58 (no HCl) to n =1.08 ( F (HCl)/ F (H 2 )=0.0104). The SiGe growth rate increases strongly with an increasing GeH 4 flow, with no influence of the actual SiH 2 Cl 2 flow. This is attributed to an increased hydrogen desorption caused by the presence of Ge atoms on the growing surface that frees nucleation sites for the incoming Ge and Si atoms. Adding HCl leads to a strong, linear decrease of the SiGe growth rate with the HCl mass flow.

The surface reaction mechanism of Si1-xGex/Si growth using SiH4 and GeH4 in UHV/CVD system was studied. The saturated adsorption and desorption of SiH4 from Si(1 0 0) surface was investigated with the help of TPD and RHEED, and it was found that all the 4 hydrogen atoms of one SiH4 molecule were adsorbed to the Si surface, which meant that the dissociated adsorption ratio was proportional to 4 power of surface vacancies. The analysis of the reaction of GeH4 was also done. A new surface reaction kinetic model on Si1-xGex/Si epitaxial growth under UHV conditions by SiH4/GeH4 was proposed based on these studies. The predictions of the model were verified by the experimental results. (C) 2000 Elsevier Science B.V. All rights reserved.

In this paper, we make use of the hydrogen passivation concept to demonstrate that the pyrolysis of disilane (Si 2 H 6 ) results in two silicon atoms and all six hydrogen atoms remaining on the surface and silane (SiH 4 ) produces one silicon atom and four hydrogen atoms on the surface. The dominant reaction pathways are identified and implications for Si film growth are discussed. The adsorption kinetics and subsequent dissociation of silane, disilane and germane during gas source molecular beam epitaxy on the Si(0 0 1) surface are studied in situ using modulated beam mass spectrometry (MBMS), temperature programmed desorption (TPD) and reflection high-energy electron diffraction (RHEED). These were also combined with the growth of various epitaxial layers involving repeated cycles of silane or disilane adsorption and hydrogen desorption with the layer thicknesses determined ex situ using X-ray diffraction (XRD) rocking curve measurements and computer simulations.

The chemical composition across strained silicon–germanium/silicon layers has been studied quantitatively using a variety of analytical electron microscopy techniques: energy-dispersive X-ray microanalysis (EDX), electron energy-loss spectroscopy (EELS), high-angle annular dark-field imaging (HAADF) and high-resolution electron microscopy (HREM). The results from these different techniques are compared. EELS and HAADF in particular are shown to be powerful methods to calculate compositional profiles from which growth information can be extracted. It is shown that the activation energy for interdiffusion of strained SiGe/Si layers is 2.3±0.3 eV, which is significantly lower than for the diffusion in bulk Si or bulk SiGe. The measured interface widths are much larger than predicted using a two-state exchange model suggesting that this model is an oversimplification. Increasing the growth temperature in chemical vapour deposition broadens SiGe/Si interfaces asymmetrically: the SiGe-on-Si interface is broadened much more than the Si-on-SiGe interface. Growth interrupts lead to Ge depletion. The growth rate of SiGe is reduced when the germane flow commences and reaches a steady-state condition only for layers wider than 10 nm. These results can be explained by hydrogen passivation of the growth surface.

Ge composition dependence on the Ge cell temperature has been studied during the growth of Si1-xGex by disilane and solid Ge molecular beam epitaxy at a substrate temperature of 500 degrees C. It is found that the composition x increases and then saturates when the Ge cell temperature increases, which is different from the composition-dependent behavior in growth at high temperature as well as in growth by molecular beam epitaxy using disilane and germane. The enhanced hydrogen desorption from a Ge site alone cannot account for this abnormal composition-variation behavior. We attribute this behavior to the increase of rate constant of H desorption on a Si site when the Ge cell temperature increases.

The growth characteristics in the initial stage of Ge epitaxy on the Si(1 0 0) epitaxial buffer layer have been investigated by ultraclean LPCVD at 350°C using GeH 4 at 0.2 and 12 Pa with H 2 or Ar as a carrier gas. When H 2 was used as a carrier gas, an incubation period was found (about 12 min at 0.2 Pa), during which Ge nuclei were formed on Si. After the incubation period layer growth of Ge film began. In the case where Ar was used as a carrier gas, the incubation period was drastically reduced without any apparent change in the layer growth rate. The nucleus size was larger and the nucleus density was lower in the case of H 2 as carrier gas. These growth characteristics are believed to be caused by the suppression of adsorption and/or decomposition of GeH 4 on the H-terminated Si surface in the case of H 2 .

We have grown silicon-germanium/silicon (Si 1-x Ge x /Si, x < 0.30) multiple quantum wells (MQWs) by gas-source molecular beam epitaxy (GSMBE) using disilane (Si 2 H 6 ) and germane (GeH 4 ) as source gases, and have characterized their structural properties by secondary ion mass spectroscopy (SIMS), X-ray diffraction (XRD) rocking curve and transmission electron microscopy (TEM) techniques. A substrate temperature of 520°C was maintained during growth resulting in a Si and SiGe growth rate-limited primarily by hydrogen desorption kinetics. Under these conditions, surface hydrogen is expected to function as a surfactant thereby enhancing interfacial abruptness at the Si/SiGe interface through suppression of Ge surface segregation. Independent of Ge composition in the Si 1-x Ge x wells, we find abrupt interfaces, as determined from XRD measurements, and sharp SIMS decay lengths of the order of 2.5 nm/decade. For nominally identical Si barriers in all samples examined, we find thicker barriers for the structures with higher Ge content in the well. For the specimens with x = 0.30 in the wells, we find a noticeable well plus barrier period variation of approximately 5%-10% as determined from XRD rocking curves, as well as TEM evidence for the onset of strain relaxation via interface undulation formation in the first quantum well of the structure. A discussion of these results in terms of hydrogen desorption kinetics is presented.

We have investigated the roughening of SiGe layers grown from disilane and germane on Si(001) using gas-source molecular beam epitaxy (GSMBE). Si 1 − x Ge x layers were grown in the temperature range of 500–650°C while the Ge concentration x was varied between 0.06–0.28. Photoluminescence spectroscopy (PL) was used to calibrate the Ge concentration in SiGe layers. During growth the SiGe surfaces were inspected with reflection high-energy electron diffraction (RHEED) and after deposition with scanning electron microscopy (SEM). At low temperatures and Ge concentrations we found smooth (2D) layers. However, for high temperatures and Ge concentrations we obtained rough {118} and {113} faceted layers (3D). Comparison with solid-source MBE (SSMBE) results (Bean et al. [J. Vac. Sci. Technol. A 2 (1984) 436]) reveal that 3D growth in GSMBE is observed for lower Ge concentrations and temperatures. This difference can be explained by the much lower growth rates used in our experiments. At higher growth rates the surface atom diffusion length is reduced and the development of the thermodynamically favourable 3D phase is suppressed.

We have investigated the epitaxial growth of Si 1 - x - yGe x C y alloys on a Si(100) surface by cold-wall ultrahigh vacuum chemical vapor deposition, using disilane (Si 2 H 6 ), germane (GeH 4 ) and acetylene (C 2 H 2 ). We have studied the growth rate and the germanium and carbon concentrations of the ternary alloy under various growth conditions. By comparing the growth of Si 1 - xGe x , Si 1 - yC y , and Si, we have presented a simple growth model. In addition, we achieved selective area growth using a SiO 2 patterned Si(100) substrate.

By means of “hybrid” Si molecular beam epitaxy (MBE), an n-type Si contact layer for an electroluminescent (EL) p-i-n diode was successfully regrown on a Si 1− x Ge x /Si single quantum well (SQW) layer. The starting undoped SQW layer was grown by gas-source MBE (GSMBE) using disilane (Si 2 H 6 ) and germane (GeH 4 ), and the n-Si contact layer was regrown by using solid-source MBE after transferring the sample through the air. A (2×1) reconstruction was observed on a GSMBE-prepared Si surface even after the sample was exposed to air for 15 h. Evidence of the excellent quality of the EL p-i-n device was provided by the sharpest emission lines, ≈ 5.5 meV, ever reported in the EL spectra of an SiGe system.

Starting with a phenomenological description of both layer growth and composition of Si 1− x Ge x mixed-crystal films deposited by a CVD process, and including the independent and first order decomposition reaction of silicon source compound as well as germanium source compound in that phenomenological view, a completed model that describes Si 1− x Ge x mixed-crystal film growth rate as well as composition is developed. It includes the successive chemical substitution of the hydrogen atoms of the germanium source compound (for instance germane) by silyl groups coming from the silicon source compound (for instance dichlorosilane), the possibility of a lower incorporation probability for germanium atoms relative to that of silicon atoms being transported by the germane intermediate, and the presence of a trapping mechanism for germanium atoms that holds them on the surface at higher deposition temperatures at which the sticking coefficient is expected to approach zero.

Growth of Ge on GaAs at reasonably high temperatures, which produces better crystallinity in the Ge, presents serious difficulties due to the dissociation of the GaAs substrate. In this paper, we describe the growth of a low-temperature buffer layer of Ge on GaAs that considerably reduces the effects of decomposition of the GaAs during high-temperature growth of Ge. Using this approach, we present the first report of highly specular, mass-transport-limited, high-temperature growth of Ge on GaAs that is comparable to the homoepitaxy of Ge, although with a reasonably high residual n-type ( ∼1018 cm-3) doping level. The factors affecting the structural, electrical and optical properties of Ge on GaAs, using such an epitaxial growth technique, were studied. Lifetime variations from very low values to about 0.45 μs were measured by a microwave technique as a function of growth conditions. Significantly, the removal of the surface oxide on the GaAs substrate prior to low-temperature buffer-layer growth, terminating the flow of germane (GeH4) during the ramp to high growth temperatures, thinner buffer layers, and high-temperature growth of Ge, were found to be important for obtaining long lifetimes.

The control of dopants, impurities and defects for very large scale integration of silicon integrated circuits requires a complex set of crystal and processing conditions to be satisfied simultaneously. In order to achieve the maximum yield and highest level of electrical performance for a given device design, we have manipulated the lattice constant and boron doping levels in CVD epitaxial silicon layers co-doped with germanium. By adjusting the ratios of germane and diborane in a dichlorosilane/hydrogen CVD reactor we can achieve extrinsic gettering using controlled introduction of interfacial misfit dislocations with Si(Ge), and buried high conducting layers which are strain-free and lattice matched to the Si substrate. A variety of these structures have been characterized using gated-diode leakage, spreading resistance profiling, MOS lifetime, cross-sectional TEM, SEM-EBIC and SIMS depth profiling.

Silicon and germanium have been selectively grown epitaxially on silicon using the thermal decomposition of SiH4 or GeH4. The silicon or germanium was grown in holes in masking layer of thermally grown SiO2. At relatively low growth temperatures, such as 700 °C for germanium and 1100 °C for silicon, the material deposited uniformly over the water surface and was single crystal in the holes in the oxide and polycrystalline on top of the oxide. At higher temperatures, above 800 °C for germanium and above 1175 °C for silicon, the material grew only in and around the holes in the oxide, where epitaxial growth was obtained. The growth process consisted of decomposition of the hydride over the complete wafer surface and migration of the silicon or germanium across the oxide surface until the material reached a hole in the oxide. This is in contrast to the situation that occurs when SiCl4 is used for selective epitaxy where control of the quasi-equilibrium conditions at the gas-solid interface determine the growth conditions.

The impurity-induced nucleation and the kinetics of the growth of filamentary crystals of silicon and germanium from silane and germane respectively have been studied in a closed system. Silicon whiskers were grown on heated substrates at temperatures between 550 and 900 °C, germanium whiskers at temperatures between 300 and 500 °C, both at hydride pressures between 5 and 100 Torr, and with Au as impurity. Whisker growth was also obtained with Ag, Cu, Ni and Pd, but not with In, Sn and Bi. The rates of growth of the whiskers in the length direction increase with increasing substrate temperature and hydride pressure, and are of the order of a hundred times higher than the rates of thickness growth of whiskers and substrate. As compared with the non-impurity aided deposition of Si and Ge from the hydrides, where there is an exponential relation between deposition rate and reciprocal temperature, the effect of the growth stimulus at the tip is reflected in a decrease of the activation energy and an increase in the pre-exponential factor. In terms of the VLS mechanism the catalyzed decomposition reaction at the V-L interface is the rate-controlling step.

The growth conditions required for the deposition of degenerate epitaxial layers of n-type germanium on n-type GaAs via the thermal decomposition of GeH4 have been established. The growth rate has been determined as a function of the deposition temperature for several germane to hydrogen ratios and as a function of the percentage of germane and arsine in the reaction mixtures. Deposition conditions necessary for the elimination of the formation of an interfering p-layer in the germanium due to the thermal breakdown of the GaAs surface during the deposition were also determined.