Presence Of Ge Atoms Research Articles

Influence of annealing atmosphere on crystallization of amorphous Si1-xGex thin film by Raman spectroscopy

The influence of annealing atmosphere on the crystallization behavior of amorphous structure in a-Si1-xGex thin films was studied with Raman spectroscopy. We annealed a-Si1-xGex (x = 0, 0.14, 0.27) thin films at 800 °C under various atmosphere and observed change in Raman spectra. We confirmed that nitrogen-annealing atmosphere promotes crystallization of the a-Si film, however, the crystallization was not promoted in the annealing under Ar atmosphere and in vacuum.In the case of a-Si thin films containing Ge atoms, the crystallization in the a-Si1-xGex (x <0.25) film was not promoted, although a-Si1-xGex (x ≥0.25) film was crystalized when the annealing in a N2 atmosphere. However, crystallization of the a-Si1-xGex (x = 0, 0.14, 0.27) were not promoted by the annealing under Ar atmosphere or in vacuum. The distortion induced by the presence of Ge atoms in the random-network of Si1-xGex, at a content below 25%, stabilizes the amorphous structure and obstructs the crystallization even in the annealing under the N2 atmosphere.

Carbon‐hydrogen related defects in SiGe observed after dc H plasma treatment

In the present study, the electrical and structural properties of two carbon‐hydrogen related DLTS levels (E42 and E262) that appear after hydrogen plasma treatment are investigated in diluted Si1−xGex alloys. E42 and E262 were previously observed in pure Si after hydrogenation by a dc hydrogen plasma. They were correlated with different charge states of a carbon–hydrogen complex, where H is located on the anti‐bonding position at the carbon atom (CH1AB). By utilizing the Laplace DLTS technique we show that the DLTS peaks E42 and E262 consist of several components in Si1−xGex. These components can be quantitatively explained by the presence of Ge atoms in the first and second nearest‐neighborhood of the CH1AB complex. The observed Laplace DLTS spectra indicate a preference of hydrogen to bond to carbon with a Ge atom in its first nearest‐neighborhood.

Multicolor photoluminescence in ITQ-16 zeolite film

Exploring the native defects of zeolites is highly important for understanding the properties of zeolites, such as catalysis and optics. Here, ITQ-16 films were prepared via the secondary growth method in the presence of Ge atoms. Various intrinsic defects of ITQ-16 films were fully studied through photoluminescence and FTIR characterizations. It was found that both the as-synthesized and calcined ITQ-16 films displayed multicolor photoluminescence including ultraviolet, blue, green and red emissions by exciting upon appropriate wavelengths. The results indicate that Si―OH and non-bridging oxygen hole centers(NBOHCs) are responsible for the origin of green and red emissions at 540―800 nm, while according to a variety of emission bands of calcined ITQ-16 film, blue emission bands at around 446 and 462 nm are attributed to peroxy free radicals(≡SiO2), ultraviolet emissions ranging from 250 nm to 450 nm are suggested originating from a singlet-to-triplet transition of two-fold-coordinated Si and Ge, respectively.

Electrical properties of diluted n- and p-Si1 − x Ge x at small x

Hall effect and conductivity measurements are taken on Si1 − x Ge x of n- and p-type at x ≤ 0.05. Much attention is given to electrical measurements over a temperature interval of 25 to 40 K where the mobility of charged carriers is strongly affected by alloy scattering. The partial mobility of electrons and holes due to this scattering mechanism is estimated for n-Si1 − x Ge x and p-Si1 − x Ge x at small x. Together with this, an effect of the presence of Ge atoms upon the ionization energy of phosphorus and boron impurities is investigated. Some points related to an inhomogeneous distribution of Ge atoms in Si1 − x Ge x are discussed.

Time-resolved plasma measurements in Ge-doped silica exposed to infrared femtosecond laser

Using a time-resolved interferometric technique, we study the laser-induced carrier-trapping dynamics in SiO${}_{2}$ and Ge-doped SiO${}_{2}$. The fast trapping of electrons in the band gap is associated with the formation of self-trapped excitons (STE). The STE trapping is doping dependent in SiO${}_{2}$. The mean trapping time of electrons excited in the conduction band was found to be significantly lower in Ge-doped silica (75 \ifmmode\pm\else\textpm\fi{} 5 fs) when compared to pure silica (155 \ifmmode\pm\else\textpm\fi{} 5 fs). At our concentration level, this indicates that the plasma properties are determined by the presence of easily ionizable states such as the presence of Ge atoms in the glass network. Therefore, we suggest that in Ge-doped silica there exist an additional trapping pathway that leads to a significantly faster excitons trapping and a higher plasma density when compared to undoped silica.

Damage creation in ion irradiated Si1−xGex/Si structures

Strained SiGe/Si structures have been proposed as substrates for fabrication of high speed metal oxide semiconductor transistors. However, influence of strain and/or presence of Ge atoms on damage creation during ion irradiation have not been explored to a significant extent. In this study, Rutherford backscattering spectrometry (RBS) was used to characterize Si1−xGex/Si structures irradiated by 140keV He+ ions at room temperature. When compared with pure Si, strained samples show enhanced damage accumulation as a function of He fluence. Channeling angular scans did not reveal any specific configuration of displacements. Possible mechanisms for enhanced damage in strained Si are discussed.

Interaction of iron with the local environment inSiGealloys investigated with Laplace transform deep level spectroscopy

Laplace transform deep level transient spectroscopy (LDLTS) is used to investigate the alloy effects on iron related deep centers in ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$. A clear buildup of alloy disorder as a function of the germanium content has been observed for the isolated interstitial iron. However, due to specific features of the interstitial tetrahedral position of iron in the cubic lattice, it is not possible to say how many Ge atoms are responsible for the alloy-induced level splitting of the electronic state of the interstitial iron related defect. The observation of alloy splitting for the iron-boron pair has been used to resolve this issue. Different shells of nearest-neighbor atoms form the alloy pattern for both the interstitial isolated iron and the iron-boron pair. We show that for the iron-boron pair the occupied state is formed when a hole is closer to iron in the case of low germanium content. For more germanium rich alloy compositions the hole is bound by boron resulting in a dramatic change in the LDLTS peak structure. In an attempt to simulate the observed patterns, the alloying effects originating from different shells containing the defect were considered. A clear tendency for iron to form a pair with boron siting in germanium rich neighborhood is demonstrated. Finally, the influence of alloying on iron motion has been investigated. Similarities in the dissociation potential barrier heights of the iron-boron pair in pure silicon and ${\mathrm{Si}}_{0.98}{\mathrm{Ge}}_{0.02}$ alloy suggest that the presence of Ge atoms induces only a second-order effect on the average diffusion barrier in alloys with low Ge content (less than 3%).

SiGe high-temperature growth kinetics in reduced pressure-chemical vapor deposition

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 2Cl 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 2Cl 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 2Cl 2 and GeH 4 flows (in order to have access to both low and high F(GeH 4)/F(SiH 2Cl 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%.

Solid phase reactions between Fe thin films and Si-Ge layers on Si

Solid phase reactions in Fe thin films on epi-Si 0.8Ge 0.2, poly-Si 0.7Ge 0.3, a-Si 0.8Ge 0.2, and a-Si 0.7Ge 0.3 layers on silicon have been investigated. The as-deposited samples were in situ annealed in the ultrahigh vacuum chamber at 400–800 °C for 30 min. The island structure was found to cause the abrupt increase in the sheet resistance of the annealed Fe/SiGe samples at 700–800 °C. The formation of FeSi islands containing a small amount of Ge is attributed to the preferential reactions of Fe with Si to Ge. As the annealing temperature was raised to 800 °C, the Fe(Si 1− x Ge x ) phase is the only phase found in the annealed Fe/epi-Si 0.8Ge 0.2 and Fe/poly-Si 0.7Ge 0.3 samples. On the other hand, at the annealing temperature above 700 °C, the β-Fe(Si 1− x Ge x ) 2 phase was observed in the annealed Fe/a-Si 0.8Ge 0.2 and Fe/a-Si 0.7Ge 0.3 but the Fe(Si 1− x Ge x ) is still the dominant phase. The results indicate that the formation of Fe disilicide was retarded by the presence of Ge atoms.

Visible photoluminescence of Ge enriched SiO x layers

This paper concentrates on results of photoluminescence (PL), Raman scattering and extended X-ray absorption fine structure (EXAFS) investigations of silicon oxide films enriched by Ge. All the spectra were analyzed both for “as prepared” silicon oxide films enriched by Ge (without Ge-quantum dots, QD) and for films after high temperature annealing in inert atmosphere with the aim of creating Ge-nano-crystallites (nc)-quantum dots. Five PL bands were discovered in Ge–SiO x systems. It is shown that the visible PL bands peaked at 1.61–1.65 eV (2), 1.75–1.80 eV (3), 2.00–2.06 eV (4) and 2.25–2.30 eV (5) do not correlate with the presence of Ge atoms or Ge-nc in the samples. The nature of the infrared PL band peaked at 1.43–1.52 eV is not clear. The intensity of this PL band increases in thermally annealed samples with increasing Ge concentration.

Effects of temperature and HCl flow on the SiGe growth kinetics in reduced pressure–chemical vapor deposition

Using a reduced pressure chemical vapor deposition cluster tool, we have studied at 20 Torr the growth kinetics of SiGe using a dichlorosilane+germane+hydrochloric acid chemistry. Adding HCl leads at 700 °C to a significant increase in the germanium content x of SiGe layers. Adopting a x2/(1−x)=n(F(GeH4)/F(SiH2Cl2)) dependence of x on the F(GeH4)/F(SiH2Cl2) mass flow ratio, this translates into an n value linearly increasing with the HCl mass flow from n=0.66 (no HCl) up to n=2.24 (F(HCl)/F(H2)=0.00625). The SiGe growth rate increases strongly with an increasing GeH4 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. Meanwhile, adding HCl leads to a strong, linear reduction of the SiGe growth rate with the HCl mass flow. As expected, the Ge concentration decreases significantly as the growth temperature increases from 650 to 750 °C. The associated n parameter depends exponentially on the reverse absolute temperature, with an “activation energy” of the order of −15 kcal mol−1. At the same time, the SiGe growth rate increases strongly as the growth temperature increases, with an activation energy dropping from 47 down to 12 kcal mol−1 as the Ge content in the film goes up (from 0% up to 27% at 700 °C).

Effect of HCl on the SiGe growth kinetics in reduced pressure—chemical vapor deposition

Abstract 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.

SiGe growth kinetics and doping in reduced pressure-chemical vapor deposition

Using a reduced pressure-chemical vapor deposition cluster tool, we have studied the growth kinetics of Si and SiGe and the n-type and p-type doping of Si with both silane and dichlorosilane chemistries. As far as Si is concerned, a conventional behavior is found for both gases, i.e. a low-temperature region where the Si growth rate is limited by the desorption of the H atoms from the growing surface (activation energy equal to 47 kcal/mol), and a high-temperature region, where the Si growth rate is mainly piloted by the incoming flow of SiH 4 or SiH 2Cl 2 (activation energy of 4 kcal/mol). The incorporation of B in Si is linear with the B 2H 6 flow (p-type doping of Si), achievable with an overall 9×10 16–4×10 19 cm −3 B ions concentration range. There is a sub-linear dependency of the P incorporation into Si with the PH 3 flow (n-type doping of Si). A 2×10 16–9×10 18 cm −3 P ions concentration range can be reached with both silicon gas sources. The growth rate of boron-doped Si is virtually unaffected by increasing B 2H 6 flow. Meanwhile, the growth rate of phosphorous-doped Si steadily drops when the PH 3 flow is increased. As far as the SiH 4+GeH 4 chemistry is concerned, the Ge concentration x in the SiGe film obeys at 650°C the following law as a function of the F(GeH 4)/F(SiH 4) mass flow ratio: x/(1− x)=2.7(F(GeH 4)/F(SiH 4)). For the SiH 2Cl 2+GeH 4 chemistry, x is linked at 750°C to the F(GeH 4)/F(SiH 2Cl 2) mass flow ratio through the following relationship: x 2/(1− x)=0.55(F(GeH 4)/F(SiH 2Cl 2)). The SiGe growth rate increases strongly with an increasing GeH 4 flow, with no apparent influence of the actual SiH 4 or SiH 2Cl 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.

Defect-formation processes in silicon doped with manganese and germanium

Deep-level transient spectroscopy has been used to study the effect of Ge atoms on the behavior of Mn in Si. It is shown that Ge atoms introduced into Si during growth manifest no electrical activity, even though their concentration is rather high: 1016–1019 cm−3. It is established that the presence of Ge atoms in the Si lattice enhances the efficiency of the formation of the deep levels E c -0.42 eV and E c -0.54 eV, which are associated with Mn in the Si lattice: the concentration of these deep levels in Si〈Ge, Mn〉 samples is a factor of 3–4 greater than in Si〈Mn〉. It is found that the presence of Ge atoms stabilizes the properties of the Mn levels in Si: They anneal more slowly than in Si〈Mn〉 by a factor of 5–6. It is assumed that the detected effects are associated with the features of the defect structure of Si doped with Ge and Mn.

Electrical properties of plasma-grown oxide on MBE-grown SiGe

The oxidation of semiconductors by RF (radio-frequency) plasma anodization offers several advantages over conventional thermal furnace oxidation, such as low process temperature and faster oxidation rate. This paper investigates the electrical properties of the plasma-grown oxide on SiGe at room temperature and compares them with thermally grown oxides of SiGe. An interface state peak has been observed at around Ev+0.75 eV. This peak is found to be caused by the presence of the SiGe layer and we present evidence that it is related to a silicon dangling bond. We have also observed that the magnitude of the voltage pulse necessary to induce avalanche electron injection increases through the presence of the SiGe layer. We believe that this is related to the increased ionization rate associated with the smaller bandgap of SiGe. The presence of Ge atoms in the plasma oxide has introduced electron traps with capture cross sections of the order of 10-15 and 10-16 cm2. Negative bias temperature stress indicates that the bonding between Ge and H is weak. This aging test also supports the theory that the interface states are acceptor-like in the upper half and donor-like in the lower half of the energy bandgap.

Interactive effects in the reactive ion etching of SiGe alloys

Reactive ion etching (RIE) of epitaxial, strained Si1−xGex alloys, x≤0.20, in fluorine-, chlorine-, and bromine-based low-pressure plasmas has been investigated. The SiGe etch rates increase for each etchant with Ge concentration, e.g., for fluorine-based RIE (CF4 and SF6) the etch rate of a Si80Ge20 alloy is ≂2x that of elemental Si. Analysis shows that the etch rate increase is not accounted for by the greater rate of gasification of Ge atoms alone but that the presence of Ge atoms in the SiGe alloy increases the rate of Si etch product formation.

Studies of the reactive ion etching of SiGe alloys

Reactive-ion etching (RIE) of epitaxial, strained Si1−xGex alloys, x≤0.20, in fluorine-chlorine-, and bromine-based low-pressure plasmas has been investigated. The reactive-ion etch rates of the Si1−xGex alloys increase with the Ge content of the alloy for most etching gases. This effect is most pronounced for fluorine (CF4 and SF6) plasmas where the etch rate of a Si80Ge20 alloy is increased by a factor of ≂2 over that of Si. The etch rate enhancement is of reduced importance for chlorine (CF2Cl2) and bromine (HBr) plasmas, where the etch rate increases by less than 50% for a Si80Ge20 alloy relative to that of elemental Si. Analysis shows that the etch rate increase is not accounted for by the greater rate of gasification of Ge atoms alone but that the presence of Ge atoms in the SiGe alloy increases the Si etch product formation rate. Directional SiGe profiles are observed for CF2Cl2 and HBr plasmas which are identical to those obtained with Si. After etching in CF4 or SF6 plasmas the Ge surface concentration of the SiGe alloy is increased relative to its bulk value and both fluorinated Si and Ge are observed by in situ x-ray photoemission spectroscopy. On the other hand, for CF2Cl2 and HBr plasmas the SiGe surface is Si rich. The effect of band-gap narrowing, strain and plasma-induced surface modifications on the etching of the SiGe alloys is discussed.

High-dose Ge implantation into 〈100〉 Si

Annealing behavior of radiation damage formed by the implantation of 75Ge + ions into silicon was measured by channelling, with concentrations of germanium up to 14 at.% in 〈100〉 Si. At higher concentrations after annealing residual damage was located both at the interface of the damaged and undamaged crystal and at the surface. The interface defect was attributed to lattice mismatch. As for the surface defects, despite reasonable implantation conditions, the effect of recoiled oxygen or carbon cannot be ruled out. The kinetics of regrowth was not affected by the presence of Ge atoms. Apart from atoms is stable damaged regions, the Ge atoms showed highly substitutional character.