Ge Growth Rate Research Articles

Revealing Atomistic Mechanisms of Gold-Catalyzed Germanium Growth Using Molecular Dynamics Simulations

The vapor-liquid-solid (VLS) method is considered a plausible technique for synthesizing germanium (Ge) nanostructures (e.g. nanowires), which have a broad range of applications due to their unique electronic properties and intrinsic compatibility with silicon. However, crystallization failures and material defects are still frequently observed in VLS processes, with insufficient understanding of their underlying mechanisms due to instrumental limitations for high-resolution in-situ characterizations. Employing an accurate interatomic potential well fitted to the gold-germanium (Au-Ge) phase diagram, we performed molecular dynamics simulations for a systematic investigation on the Au-catalyzed growth process of Ge crystals. From the simulations, relationships were established between the overall Ge growth rate and several main synthesis conditions, including substrate crystallographic orientation, temperature and Ge supersaturation in liquid. The dynamical behaviors of Ge atoms near the liquid-solid growing interface were captured, from which the atom surface stability and exchange rate were estimated for quantifying the atomistic details of the growth. These interface properties were further linked to the surface morphologies, to explain the observed orientation-dependent growing modes. This study sheds new lights into the understanding of the VLS growth mechanisms of Ge crystals, and provides scientific guidelines for designing innovative synthesis methods for similar nanomaterials.

An In-Depth Study of the Boron and Phosphorous Doping of GeSn

We have investigated the in situ doping of GeSn with Ge2H6, SnCl4, B2H6 (p-type) or PH3 (n-type) at 349 °C, 100 Torr on Ge Strain-relaxed Buffers, themselves on Si(001) substrates. Our aim was to replace the boron and phosphorous doped Ge layers used in previous pin structures with GeSn:B and GeSn:P. The Sn content from Wavelength Dispersive X-ray Fluorescence (WDXRF) was constant around 6.5% for low F(B2H6)/F(Ge2H6) and F(PH3)/2*F(Ge2H6) Mass-Flow Ratios (MFRs). It fell down to 4.9% (GeSn:B) and 6.0% (GeSn:P) for higher MFRs due to the dopant precursors that catalyzed the Ge Growth Rate component. The B atomic concentrations (from Secondary Ion Mass Spectrometry (SIMS)) increased almost linearly with the MFR, reaching values of at most 6.3 × 1019 cm−3. B atoms were almost fully electrically active based on Electrochemical Capacitance Voltage (ECV) measurements. WDXRF and SIMS also gave us access to the atomic P concentrations, with values as high as 3.9 × 1020 cm−3. Maybe because of the formation of SnmPnV nanoclusters, the P electrical activation decreased for the highest flows. Only the GeSn:B layers grown at the three highest MFRs exhibited some B and/or Sn surface segregation. Otherwise, a smooth surface with a cross hatch along 〈110〉 was present.

Boron and Phosphorous Doping of GeSn for Photodetectors and Light Emitting Diodes

With an electrically pumped group IV laser operating at room temperature as a long term goal, we would like to replace the boron and phosphorous doped Ge layers used in previous pin structures with GeSn:B and GeSn:P. We have thus investigated the in-situ doping of GeSn with Ge2H6, SnCl4, B2H6 (p-type) or PH3 (n-type) at 349°C, 100 Torr on Ge Strain-relaxed Buffers, themselves on Si(001) substrates. The Sn content from Wavelength Dispersive X-Ray Fluorescence (WDXRF) was constant around 6.5% for low F(B2H6)/F(Ge2H6) and F(PH3)/2*F(Ge2H6) Mass-Flow Ratios (MFRs). It fell down to 4.6% (GeSn:B) and 5.6% (GeSn:P) for higher MFRs. This drop was likely due to the dopant precursors that catalyzed the Ge Growth Rate component. Substitutional B and P contents were extracted from the differences between real Sn contents from WDXRF and “apparent” Sn contents from X-Ray Diffraction (compressive strain compensation by small B and P atoms). The B substitutional concentrations increased sub linearly with the MFR, reaching values of at most 5.2x1019 cm-3. Meanwhile, the P substitutional concentration increased linearly with the MFR, up to 2.2x1020 cm-3. WDXRF gave us also access to the atomic P concentrations, with values as high as 2.2x1020 cm-3 A cross-hatch along <110> was otherwise present on the surface of the various GeSn:B and GeSn:P layers, which were rather smooth. Only the GeSn:B layers grown at the three highest MFRs exhibited some B and/or Sn surface segregation.

Growth conditions of metal-catalyzed, laterally grown Ge films on Si

Low threading-dislocation-density and highly relaxed Ge films have been grown laterally on Si using the vapor-liquid-solid mechanism. To expand the application of this technique, larger film sizes and reduced growth times are needed. One way to increase Ge film sizes is to increase the growth rate by using a high GeH4 flux or high growth temperature. However, it was found that a high Ge growth rate tended to lead to the uncatalyzed growth of GeH4 and longer growth times also increased the possibility of uncatalyzed growth. Moreover, under the condition of higher growth rate, uncatalyzed growth appears in a shorter time. Therefore, a low growth rate is suggested to suppress the uncatalyzed growth of Ge while a relatively long growth time is required to increase the size and yield (percentage of micro-crucibles with Ge films) of the films. The growth conditions were investigated and then optimized in this study, and it has been found that the better results were obtained at 375 °C, 3 sccm GeH4 for 2 hours and 400 °C, 2 sccm GeH4 for 2 hours.

Extra-long and taper-free germanium nanowires: use of an alternative Ge precursor for longer nanostructures

One of the challenges in the development of germanium nanowires (Ge NWs) is to increase their length beyond the 10 μm limit without enlarging the NW diameter, i.e. minimizing the tapering. Here we report how it is possible to overcome this hurdle by using isobutyl germane (iBuGe) as a metal organic precursor during MOCVD growth, instead of the commonly used germane. We have grown and characterized by transmission electron microscopy, scanning electron microscopy and Raman various samples and we have analyzed the effect of growth time, precursor flux and growth temperature on the NW length. The use of iBuGe coupled to optimized growth conditions permitted to obtain Ge NWs with lengths up to 30 μm with minimal tapering. To explain why a new precursor has this impact on the morphology of the NWs we consider two possible causes: (i) the role of carbon radicals produced by isobutyl decomposition and (ii) the reduced growth rate of Ge on the sidewalls. On the basis of Raman characterization and temperature-dependence of tapering, we conclude that the reduced tapering is probably due to lower growth rates on the sidewalls.

In situ phosphorus-doped Ge1−xSnx layers grown using low-temperature metal-organic chemical vapor deposition

We report the metal-organic chemical vapor deposition method for epitaxy of n+-Ge and Ge1−xSnx layer with an electron concentration as high as 2 × 1019 cm−3 by in situ phosphorus (P) doping. In this study, we examined MO precursors of tertiary-butyl-germane (t-BGe), tri-butyl-vinyl-tin (TBVSn), and two kinds of P precursors of tri-ethyl-phosphine (TEP) and tertiary-butyl-phosphine (t-BP). We have investigated crystalline and electrical characteristics of P-doped Ge and Ge1−xSnx layers. In the case of using TEP, the P-doped Ge0.98Sn0.02 epitaxial layer grown at 320 °C on virtual Ge substrate was demonstrated, in which the chemical P-incorporation as high as 1 × 1019 cm−3 and the full electrical activation of P. By using t-BP instead of TEP, the chemical P-incorporation as high as 8.1 × 1019 cm−3 was achieved for Ge epitaxial layer grown at 300 °C. It is found that the activation energy of the growth rate of Ge and P with t-BGe, TEP, and t-BP was estimated to be 1.0−1.2, 2.1, and 1.1 eV, respectively. The precursor combination of t-BGe and t-BP has a wider temperature window for a lower growth temperature. In situ P-doping with t-BP enables us to grow the Ge0.975Sn0.025 epitaxial layer with an electron concentration as high as 1.7 × 1019 cm−3 at the temperature as low as 300 °C. For both cases of TEP and t-BP, we observed that increasing Sn content significantly reduces the P-incorporation, which is not common phenomenon in a conventional CVD growth.

Effects of Ge growth rate and temperature on C-mediated Ge dot formation on Si (100) substrate

Effects of Ge growth rate and growth temperature were investigated on C-mediated formation of Ge quantum dots (QDs) on Si (100) substrate. The samples were prepared by a solid-source molecular beam epitaxy. Ge dots were scaled down and dot density increased with increasing Ge growth rate up to about 2nm/min, and dot size and density were saturated beyond that. The effect of Ge growth temperature was strong at slow Ge growth rate, while it was insensitive at fast Ge growth rate. Consequently, minimum mean dot diameter of about 25nm and maximum dot density of about 1.1×1011cm−2 were obtained at growth temperature of 450°C. These results suggest that the Ge growth condition of fast growth rate or low growth temperature acts effectively to increase the nucleation probability of Ge adatoms and consequently enables to form Ge QDs by maximizing the effects of C-mediated surface reconstruction.

Very Low Temperature Epitaxy of Heavily In-situ Phosphorous Doped Ge Layers and High Sn Content GeSn Layers

Combining in-situ phosphorous doping and tensile strain yield a direct bandgap-like behavior in germanium. The electrons given by the n-type impurities to the strained Ge crystalline lattice then occupy the L valleys of the conduction band, exalting fast, direct transitions between the Γ valley of the conduction band and the valence band. Using low temperatures (e.g. 400°C) and relatively high pressures (100 Torr, typically) enabled us to promote P incorporation in Ge:P layers [1]. With the conventional precursors used (GeH4 and PH3), we could not go to temperatures lower than 400°C, however. We have recently quantified the interest of using digermane (Ge2H6) in order to enhance the Ge growth rate at temperatures 425°C and lower [2] (by 5 to 10 orders of magnitude compared to GeH4). We have thus used digermane and phosphine (PH3) to grow Ge:P layers at 350°C, 100 Torr on top of slightly p-type {Ge Strain Relaxed Buffer / Si (001) substrate} stacks. The F(Ge2H6)/F(H2) Mass-Flow Ratio (MFR) and the growth duration were fixed (1.98x10-4 and 30 minutes, respectively). The process parameter varying was the PH3 mass-flow. We have first of all evidenced a Ge:P growth rate increase with the PH3 mass-flow (Figure 1), from 5 nm.min-1 for intrinsic Ge up to 11 nm.min-1 for the highest PH3 mass-flow probed. This could be due to (i) the catalysis of H desorption from the surface by P atoms, freeing sites for growth or/and (ii) a local surface temperature increase, caused by exothermal reactions [3]. All samples were golden and mirror-like under grazing light. Note that the situation was somewhat different at 400°C, 100 Torr with a GeH4 + PH3 chemistry. A transition from smooth/mirror-like to rough/milky surfaces and a sudden Ge:P growth rate drop were then evidenced for F(PH3)/F(H2) above 10-3 [4]. Conventional ω-2θ scans around the (004) XRD order were performed on those Ge:P layers. The resulting profiles are provided in Figure 2. For the highest two PH3 mass-flows probed, we obtained well-defined, intense Ge:P layer peaks (together with Pendellösung fringes on each side for the highest doping). We were thus able, from their angular position, to calculate the associated substitutional P concentrations, 2.7x1020 and 6.5x1020 cm-3. We have then performed SIMS depth profiling and four points probe measurements in order to gain access to the atomic and electrically active P concentrations in our Ge:P samples (Figure 3). As expected, the atomic P concentration monotonically increases with the PH3 mass-flow, from 9x1018 cm-3 for the lowest PH3 flow, up to 5x1020 cm-3 for the highest one. This increase slows down for F(PH3)/F(H2) MFRs above 2x10-6, however (in-line with Fig. 1 Ge:P growth rate evolution). The substitutional P concentrations (from XRD) measurements, are close to the atomic values. The vast majority of the P atoms thus seem to be substitutional. The evolution of the P+ ion concentration with the PH3 flow is somewhat peculiar. At first, it increases with the phosphine flow. The highest P+ concentration, 7.5x1019 cm-3, was obtained for F(PH3)/F(H2) = 1.25x10-6. This value is nearly 4 times higher than the value obtained at 400°C with GeH4 (~2x1019 cm-3). For higher PH3 flows, we then have a definite decrease of the P+ ions concentration. This could be due to an increase of point defects in the Ge:P crystal lattice.Finally, we have used AFM (Figure 4) in order to confirm that the Ge:P layers were smooth and featureless; the surface root mean square (rms) roughness and Z range associated with 20×20 μm² images of the most highly doped layer of the series were equal to 0.8 and 7.3 nm only, respectively. Small islands (density close to 1.6x107 cm−2) were by contrast present on the surface of intrinsic Ge layers.The high phosphorous-doping obtained here is very interesting to boost the optical performances of Ge. Another method in order to obtain a direct bandgap in group-IV semiconductors is to alloy Ge with Sn. GeSn layers have recently been shown to have a direct bandgap provided that the Sn content is high enough (12%) and the built-in strain low. This in mind, we will present some data on high Sn content (in the 6% to 10% range), compressively-strained GeSn layers we have grown at 325°C, 100 Torr on Ge SRBs (thanks to Ge2H6 and SnCl4). [1] J.M. Hartmann et al., J. Cryst. Growth 347 (2012) 37. [2] J. Aubin et al., J. Cryst. Growth, accepted (April 2016); doi: 10.1016/j.jcrysgro.2016.04.018. [3] D. Grützmacher et al., ECS Trans. 64 (11) (2014) 85. [4] J.M. Hartmann et al., Thin Solid Films 602 (2016) 13. Figure 1

Very low temperature epitaxy of Ge and Ge rich SiGe alloys with Ge2H6 in a Reduced Pressure – Chemical Vapour Deposition tool

We have studied the very low temperature epitaxy of pure Ge and of Ge-rich SiGe alloys in a 200mm industrial reduced pressure chemical vapour deposition tool. We have, first of all, benchmarked germane (GeH4) and digermane (Ge2H6) for the growth of pure Ge. Used Ge2H6 instead of GeH4 enabled us to dramatically increase the Ge growth rate at temperatures 425°C and lower (5.6nmmin−1 compared to 0.14nmmin−1 at 350°C with a Ge2H6 mass-flow one fourth that of GeH4). We have also evaluated at 400°C, 100Torr, the impact of the GeH4 or Ge2H6 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 (Si2H6) or dichlorosilane (SiH2Cl2) in order to study the GeSi growth kinetics at 475°C, 100Torr. While the SiH2Cl2 mass-flow did not have any clear influence on the GeSi growth rate (with a 14nm min−1 mean value, then), a Si2H6 mass-flow increase resulted in a slight GeSi growth rate increase (from 11nmmin−1 up to 14nmmin−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.

Modeling of kinetically limited growth rate for solution-synthesized germanium nanocrystals

Solution synthesis is a common method for preparing semiconductor nanocrystals (NCs). For such solution synthesis, many investigations have considered diffusion-limited growth, in which the diffusion of reactants through the boundary layer (BL) limits the NC growth rate. These studies often model the growth rate with a diffusion BL thickness much larger than the NC size and with unphysically low diffusion constants on the order of 10−12 cm2 s−1. In this work, we have examined the growth of Ge NCs synthesized by injecting Ge amide precursors into a solution of 1-octadecene, oleylamine, and hexadecylamine. We have previously established this low-temperature, low-pressure synthesis route. The resulting Ge growth rate compares well with our model, in which we consider both BL diffusion and surface kinetics of Ge precursors and organic ligand adsorbates. Our modeling results suggest that the NC growth is limited not by diffusion, but by the surface adsorption and desorption kinetics. The BL thickness in the stirred reaction vessel is calculated to be on the same order of magnitude as the crystal radius; therefore, the surface kinetics cannot be ignored. Furthermore, the synthesis temperature is near 300 °C, where the Ge monomer diffusion coefficient within the growth solution is substantially increased and estimated to be on the order of 10−5 cm2 s−1. These considerations agree well with our experimentally measured growth rate and strongly suggest that the NC size evolution is controlled primarily by the surface kinetics.

Ultra-smooth epitaxial Ge grown on Si(001) utilizing a thin C-doped Ge buffer layer

Here, we present work on epitaxial Ge films grown on a thin buffer layer of C doped Ge (Ge:C). The growth rate of Ge:C is found to slow over time and is thus unsuitable for thick (&amp;gt;20 nm) layers. We demonstrate Ge films from 10 nm to &amp;gt;150 nm are possible by growing pure Ge on a thin Ge:C buffer. It is shown that this stack yields exceedingly low roughness levels (comparable to bulk Si wafers) and contains fewer defects and higher Hall mobility compared to traditional heteroepitaxial Ge. The addition of C at the interface helps reduce strain by its smaller atomic radius and its ability to pin defects within the thin buffer layer that do not thread to the top Ge layer.

In Situ Boron (B) Doped Germanium (Ge:B) Grown on (100), (110), and (111) Silicon: Crystal Orientation and B Incorporation Effects

We investigate the growth of in situ boron (B) doped Ge (denoted as Ge:B) on Si(100), (110) and (111) substrates at low temperature using an ultra-high vacuum chemical vapor deposition (UHVCVD) tool. The growth rate of Ge:B on Si(100) is higher than that on Si(110) at 320 ˚C. The growth of Ge:B on Si(111) achieves 3D quantum dots at 320 ˚C and continuous film at 300 ˚C. The growth rate of Ge:B on Si(111) at 300 ˚C is much lower than other two orientations at 320 ˚C. For all the orientations, Ge:B shows a higher growth rate than intrinsic Ge.

Recipes for the fabrication of strictly ordered Ge islands on pit-patterned Si(001) substrates

We identify the most important parameters for the growth of ordered SiGe islands on pit-patterned Si(001) substrates. From a multi-dimensional parameter space we link individual contributions to isolate their influence on ordered island growth. This includes the influences of: the pit size, pit depth and pit period on the Si buffer layer and subsequent Ge growth; the pit sidewall inclination on Ge island growth; the amount of Ge on island morphologies as well as the influences of the pit-size homogeneity, the pit period, the Ge growth temperature and rate on island formation. We highlight that the initial pit shape and pit size in combination with the growth conditions of the Si buffer layer should be adjusted to provide suitable preconditions for the growth of Ge islands with the desired size, composition and nucleation position. Furthermore, we demonstrate that the wetting layer between pits can play the role of a stabilizer that inhibits shape transformations of ordered islands. Thus, dislocation formation within islands can be delayed, uniform arrays of one island type can be fabricated and secondary island nucleation between pits can be impeded. These findings allow us to fabricate perfectly ordered and homogeneous Ge islands on one and the same sample, even if the pit period is varied from a few hundred nanometres to several micrometres.

Structural, electrical and optical properties of in-situ phosphorous-doped Ge layers

We have studied the impact of temperature and pressure on the structural and electronic properties of Ge:P layers grown with GeH4+PH3 on thick Ge buffers, themselves on Si(001). The maximum phosphorous atomic concentration [P] exponentially decreased as the growth temperature increased, irrespective of pressure (20Torr, 100Torr or 250Torr). The highest values were however achieved at 100Torr (3.6×1020cm−3 at 400°C, 2.5×1019cm−3 at 600°C and 1019cm−3 at 750°C). P atomic depth profiles, “box-like” at 400°C, became trapezoidal at 600°C and 750°C, most likely because of surface segregation. The increase at 100Torr of [P] with the PH3 mass-flow, almost linear at 400°C, saturated quite rapidly at much lower values at 600°C and 750°C. Adding PH3 had however almost no impact on the Ge growth rate (be it at 400°C or 750°C). A growth temperature of 400°C yielded Ge:P layers tensily-strained on the Ge buffers underneath, with a very high concentration of substitutional P atoms (5.4×1020cm−3). Such layers were however rough and of rather low crystalline quality in X-ray Diffraction. Ge:P layers grown at 600°C and 750°C had the same lattice parameter and smooth surface morphology as the Ge:B buffers underneath, most likely because of lower P atomic concentrations (2.5×1019cm−3 and 1019cm−3, respectively). Four point probe measurements showed that almost all P atoms were electrically active at 600°C and 750°C (1/4th at 400°C). Finally, room temperature photoluminescence measurements confirmed that high temperature Ge:P layers were of high optical quality, with a direct bandgap peak either slightly less intense (750°C) or more intense (600°C) than similar thickness intrinsic Ge layers. In contrast, highly phosphorous-doped Ge layers grown at 400°C were of poor optical quality, in line with structural and electrical results.

ICP 표면 처리된 Si 기판 위에 성장된 Ge 층의 초기 성장 상태 연구

(Received June 27, 2011)(Revised July 13, 2011)(Accepted July 15, 2011)Abstract We have investigated the effect of inductively coupled plasma (ICP) treatment on the early growth stage ofheteroepitaxial Ge layers grown on Si(100) substrates using low pressure chemical vapor deposition (LPCVD). The Si(100)substrates were treated by ICP process with various source and bias powers, followed by the Ge deposition. The ICPtreatment led to the enhancement in the coalescence of Ge islands. The growth rate of Ge on Si(100) with ICP surfacetreatment is about 5 times higher than that without ICP surface treatment. A missing dimer caused by the ICP surfacetreatment can act as a nucleation site for Ge adatoms, which could be responsible for the improvement in growth behaviorof Ge on Si(100) substrates.Key wordsICP, SEM, Island, Coalescence, LPCVD, Germanium, Silicon, missing dimer

Reduced pressure chemical vapor deposition of Ge thick layers on Si(0 0 1), Si(0 1 1) and Si(1 1 1)

We have carried out an in-depth structural study of Ge thick layers grown using the so-called “LT/HT” approach on Si(0 0 1), Si(0 1 1) and Si(1 1 1) wafers. The low temperature (400 °C) adopted for the first Ge layer plastically relaxes the strain in the Ge film without 3D islanding. The high temperature (750 °C) used for the growth of the second, topmost, Ge layer lowers the dislocation density and reduces the overall deposition time. High temperature thermal cycling (in-between 750 and 890 °C) was called upon to further reduce the amount of defects in the layers. Ge growth rates on (0 0 1) were consistently higher than the ones on (1 1 1), which were themselves higher than on (0 1 1) (be it at 400 °C, 100 Torr or at 750 °C, 20 Torr). The surfaces of Ge (0 0 1) layers were rather flat, as attested by their small root mean square (rms) roughness and Z ranges (<1 and 10 nm, respectively). By contrast, Ge (0 1 1) (Ge (1 1 1)) thick layers were really rough, with rms roughness and Z ranges typically 30 (60) times higher than on (0 0 1). Almost all Ge layers were in a tensile-strain configuration, with macroscopic degrees of strain relaxation in-between 101% and 106% (slightly higher on (1 1 1) than on (0 0 1) and on (0 1 1), however). Misfit dislocations were found (by cross-sectional transmission electron microscopy) to be confined in the first few hundreds of nanometres of 2.5 μm thick Ge layers on Si(0 0 1). As far as 2.5 μm thick Ge layers on (0 1 1) and (1 1 1) are concerned, numerous {1 1 1} stacking faults were present at the Ge/Si interface and also threading all the way to the surface. The threading “defect” density, which is close to 10 7 cm −2 on (0 0 1), is around 8×10 8 cm −2 on (0 1 1) and roughly 2×10 9 cm −2 on (1 1 1). The higher defect density on (0 1 1) and (1 1 1) is likely due to 60° misfit dislocations dissociation (into 30° and 90° partial dislocations). For such surface orientations, the 90° partial dislocation is expected to lead with in its trail the 30° partial dislocation (hence the stacking faults multiplication).

In-Situ HCl Etching and Selective Epitaxial Growth of B-doped Ge for the Formation of Recessed and Raised Sources and Drains

The aim being the integration of either recessed or raised Ge:B Sources and Drains(S/Ds), we have studied the growth kinetics and the insitu boron doping of Ge in Reduced Pressure- Chemical Vapour Deposition. The Ge growth rate at 400ºC, 60 Torr on blanket Si(001) is lower when adding HCl to GeH4. The B atoms concentration increases linearly with the F(B2H6)/F(GeH4) mass flow ratio (maximum: 3.5x1019cm3). 20% to 40% of (almost all) the B atoms are electrically active in Ge:B layers grown at 400ºC (subsequently annealed at 750ºC under H2 for 10 minutes). The macroscopic degree of strain relaxation R of as grown Ge layers increases slowly from 92% up to 100% as the Ge layer thickness increases. We have also studied the kinetics of the insitu HCl etching at 20 Torr of recess in the Si active regions of patterned wafers.

Growth mechanism of Si nanowhiskers and SiGe heterostructures in Si nanowhiskers: X-ray scattering and electron microscopy investigations

Silicon nanowhiskers have been grown by molecular beam epitaxy on Si (111) by vapor-liquid-solid mechanism induced by gold droplets. Very thin Ge containing layers have been incorporated in Si nanowhiskers in order to grow SiGe heterostructures. Si and Ge growth rate in nanowhiskers, shape, and sidewall facets of nanowhiskers have been investigated by scanning electron microscopy and grazing incidence small angle x-ray scattering. Anomalous grazing incidence x-ray diffraction and transmission electron microscopy observations show a strong intermixing of Si with Ge in nanowhiskers and formation of SiGe heterostructures which are highly strained to Si.

Effect of the growth rate on the morphology and structural properties of hut-shaped Geislands in Si(001)

The effect of Ge deposition rate on the morphology and structural properties of self-assembledGe/Si(001) islands was studied. Ge/Si(001) layers were grown by solid-source molecular-beam epitaxyat 500 °C.We adjusted the Ge coverage, 6 monolayers (ML), and varied the Ge growth rate by a factor of 100,R = 0.02–2 ML s−1, to produce films consisting of hut-shaped Ge islands. The samples were characterized byscanning tunnelling microscopy, Raman spectroscopy, and Rutherford backscatteringmeasurements. The mean lateral size of Ge nanoclusters decreases from 14.1 nm atR = 0.02 ML s−1 to9.8 nm at R = 2 ML s−1. The normalized width of the size distribution shows non-monotonic behaviour as a function ofR and has a minimumvalue of 19% at R = 2 ML s−1. Ge nanoclusters fabricated at the highest deposition ratedemonstrate the best structural quality and the highest Ge content(∼0.9).

Application of selective epitaxy for formation of ultra shallow SiGe-based junctions

Selective epitaxial growth (SEG) of B-, P- and As-doped Si 1 − x Ge x (0.12 < x < 0.26) layers on patterned substrates, aimed for source/drain ultra shallow junctions was investigated. The SiGe layers were deposited selectively on Si surface that is either unprocessed or previously in situ etched by HCl in the same run in a reduced pressure chemical vapor deposition reactor. In these investigations selectivity mode, pattern dependency (loading effect), defect generation and dopant incorporation in SiGe layers have been discussed. It was demonstrated that the growth rate increased in presence of B in SiGe while it decreased for P- and As-doped layers. The amount of Ge was constant for B-doped samples while it increased for As- and P-doped SiGe layers. The epitaxial quality was dependent on the Ge amount, growth rate and dopant concentration. The selectivity mode of the growth was dependent on B partial pressure, however, no effect was observed for P- or As-doping in SiGe layers. A resistivity value of ∼10 −3 Ω cm was obtained for B- and P-doped SiGe layers with optimized growth parameters.