Strain Ge Research Articles

Evaluation of Thermal Transport Characteristics of Three-Dimensional Self-Ordered Multilayered Silicon-Germanium Nanodots

1. Background and purpose Silicon-germanium (SiGe) alloys have much lower thermal conductivity than Si and Ge single crystals and are expected to be candidates for next-generation thermoelectric device materials of internet of things society. It is important to achieve both high carrier mobility and low thermal conductivity on the basis of the dimensionless figure of merit [1]. There are several studies on the thermoelectric properties of SiGe with low-dimensional structures such as superlattice and nanodots [2,3] to dramatically decrease thermal conductivity. However, the relationship between the nanoscale thermal properties and the phonon scattering mechanism of self-ordered multilayer SiGe nanodots with high uniformity grown by Stranski-Krastanov [4] mode is unclear. In this study, we demonstrated the thermal transport characteristics of the self-ordered multilayer SiGe nanodots. 2. Experiments Si/SiGe superlattice and nanodots samples were fabricated by reduced pressure chemical vapor deposition. We set to 20 cycles of Si0.65Ge0.35 / Si superlattice, the staggered Si0.65Ge0.35 nanodots (alternately stacked) and the dot-on-dot Si0.65Ge0.35 nanodots (vertically stacked) by changing growth temperature and precursors for Si spacer growth [4], as shown in Fig. 1. Thermal properties were evaluated by the Time Domain Thermoreflectance (TDTR) method. The strain states and Ge fraction were evaluated by Raman spectroscopy. The focal length and wavenumber resolution of the Raman spectrometer were 2,000 mm and 0.1 cm-1, respectively. The excitation light source was a green laser (wavelength: 532 nm). We obtained the Raman spectra of Si-Si, Si-Ge, and Ge-Ge vibrational modes derived from the SiGe regions. 3. Results and discussion Figure 2 shows the thermal conductivity for the SiGe region of the superlattice and nanodots (dot-on-dot and staggered structures) obtained by TDTR method. We found that the SiGe nanodots with the dot-on-dot structure have the highest thermal conductivity, while the SiGe nanodots with the staggered structure and SiGe superlattice have almost the same thermal conductivity. We consider that the heat flow easily penetrates from the top (surface) to the bottom (Si substrate interface) in the dot-on-dot structures. On the other hand, it is possible that the staggered SiGe nanodots can play a sufficient role as a phonon scatterer compared to the dot-on-dot structures since the superlattice structure and the staggered SiGe nanodots have almost the same thermal properties. In conclusion, we demonstrated the possibility of controlling phonon scattering by changing the arrangement of the self-ordered multilayer SiGe nanodots. Acknowledgement This work was supported by JSPS KAKENHI Grant Number 21K14201, Japan.

Strain Modulation of Selectively and/or Globally Grown Ge Layers.

This article presents a novel method to grow a high-quality compressive-strain Ge epilayer on Si using the selective epitaxial growth (SEG) applying the RPCVD technique. The procedures are composed of a global growth of Ge layer on Si followed by a planarization using CMP as initial process steps. The growth parameters of the Ge layer were carefully optimized and after cycle-annealing treatments, the threading dislocation density (TDD) was reduced to 3 × 107 cm−2. As a result of this process, a tensile strain of 0.25% was induced, whereas the RMS value was as low as 0.81 nm. Later, these substrates were covered by an oxide layer and patterned to create trenches for selective epitaxy growth (SEG) of the Ge layer. In these structures, a type of compressive strain was formed in the SEG Ge top layer. The strain amount was −0.34%; meanwhile, the TDD and RMS surface roughness were 2 × 106 cm−2 and 0.68 nm, respectively. HRXRD and TEM results also verified the existence of compressive strain in selectively grown Ge layer. In contrast to the tensile strained Ge layer (globally grown), enhanced PL intensity by a factor of more than 2 is partially due to the improved material quality. The significantly high PL intensity is attributed to the improved crystalline quality of the selectively grown Ge layer. The change in direct bandgap energy of PL was observed, owing to the compressive strain introduced. Hall measurement shows that a selectively grown Ge layer possesses room temperature hole mobility up to 375 cm2/Vs, which is approximately 3 times larger than that of the Ge (132 cm2/Vs). Our work offers fundamental guidance for the growth of high-quality and compressive strain Ge epilayer on Si for future Ge-based optoelectronics integration applications.

Research progress in the epitaxial growth of silicon-based group IV materials, and their light emitters and photodetectors

Silicon-based optoelectronic integrated circuits, which are composed of silicon-based light sources, photodetectors, light modulators, and other modules, are core technologies in the recent information era. Silicon is the cornerstone of microelectronic integration, but it encounters issues with optoelectronic integration. First, as an indirect bandgap material, silicon is difficult to be used in high-efficiency light sources, which is still currently the biggest challenge. Second, the absorption coefficient of silicon in the near-infrared communication band is very low, so it is not suitable for the near-infrared photodetectors. Silicon-compatible group IV materials can achieve direct band through band engineering. They have a high absorption coefficient in the near-infrared and have attracted extensive attention of researchers. In this paper, the research progress of epitaxial growth of silicon-based materials, and their light emitters and photodetectors, are reviewed. The growth technologies of Ge, SiGe/Ge heterojunction, quantum wells, and GeSn quantum dots are introduced. Based on the above silicon-based group IV heterostructure materials, a new method for modulating the height of the contact barrier between metal and semiconductor was proposed. Also, various photodetectors with different structures were developed. The lateral heterojunction LED and vertical resonant-cavity LED, including dual active regions compatible with traditional CMOS processes, were developed. The luminescence performance of the devices was improved effectively and the luminescence gain of strain Ge was observed.

Biotransformation of ginsenoside Rb1 to Gyp-XVII and minor ginsenoside Rg3 by endophytic bacterium Flavobacterium sp. GE 32 isolated from Panax ginseng.

The rare ginsenoside Rg3 is attracting more attention because of its good physiological activity and urgent need. There are many pathways to obtain ginsenoside Rg3, including chemical and biological methods. Among these, the conversion of the protopanaxadiol-type ginsenosides by microbial hydrolysis is a trend due to its high efficiency and mild conditions. For effectively extracting from the other panaxadiol saponins, the conversion process for ginsenoside Rg3 was investigated using β-glycosidase-producing endophytic fungus in Panax ginseng in this study. The metabolic pathways are as follows: ginsenoside Rb1→Gyp-XVII and ginsenoside Rb1→ginsenoside Rd→ginsenoside Rg3. Phylogenetic analysis of 16S rDNA gene sequence, showed that GE 32 strain belonged to Flavobacterium species. These results suggest that the process of rare ginsenoside Rg3 production by endophytic bacteria GE 32 is efficient for the industrial production and application. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on cultivable β-glycosidase-producing endophytic bacteria from Panax ginseng. Flavobacterium sp. GE32 could convert major ginsenoside Rb1 into Gyp-XVII and minor ginsenoside Rg3. Strain GE 32 has potential to be applied on the preparation for minor ginsenoside Rg3 in pharmaceutical industry.

Biotransformation of ginsenoside Rb1 to ginsenoside Rg3 by endophytic bacterium Burkholderia sp. GE 17-7 isolated from Panax ginseng

To isolate a novel endophytic bacterium from Panax ginseng that could have excellent properties in converting ginsenoside Rb1 to ginsenoside Rg3. Based on a 16S rDNA gene sequence, the strain named GE 17-7 was identified as Burkholderia sp. This strain has shown the highest activity in converting ginsenoside Rb1 to 20(S)-ginsenoside Rg3. During the biotransformation of ginsenoside Rb1, the final metabolite was identified by nuclear magnetic resonance analysis and the transformation pathway of ginsenoside Rb1 was also identified by thin-layer chromatography and high performance liquid chromatography analysis in this study. We have successfully isolated a β-glucosidase-producing endophytic bacterium GE 17-7 from P. ginseng. Ginsenoside Rg3 was produced by strain GE 17-7 from ginsenoside Rb1 via ginsenoside Rd. This is the first report of the conversion of major ginsenoside Rb1 into minor ginsenoside Rg3 by fermentation with Burkholderia sp. endophytic bacteria in P. ginseng. These results suggest a new preparation method for ginsenoside Rg3 using strain GE 17-7 in the pharmaceutical industry.

Analytical threshold voltage model for strained silicon GAA-TFET**Project supported by the National Natural Science Foundation of China (Grant No. 61474085).

Tunnel field effect transistors (TFETs) are promising devices for low power applications. An analytical threshold voltage model, based on the channel surface potential and electric field obtained by solving the 2D Poisson’s equation, for strained silicon gate all around TFETs is proposed. The variation of the threshold voltage with device parameters, such as the strain (Ge mole fraction x), gate oxide thickness, gate oxide permittivity, and channel length has also been investigated. The threshold voltage model is extracted using the peak transconductance method and is verified by good agreement with the results obtained from the TCAD simulation.

Biotransformation of ginsenoside Rb1 to ginsenoside C-K by endophytic fungus Arthrinium sp. GE 17-18 isolated from Panax ginseng.

This research aimed to isolate β-glycosidase-producing endophytic fungus in Panax ginseng to achieve biotransformation of ginsenoside Rb1 to ginsenoside C-K. Of these 15 β-glucosidase-producing endophytic fungus isolated from ginseng roots, a β-glucosidase-producing endophytic fungi GE 17-18 could hydrolyse major ginsenosides Rb1 to minor ginsenoside C-K with metabolic pathways: ginsenoside Rb1→ginsenoside Rd→ginsenoside F2→ginsenoside C-K. Phylogenetic analysis of ITS gene sequences indicated that the strain GE 17-18 belongs to the genus Arthrinium and is most closely related to Arthrinium sp. HQ832803.1. This is the first study to provide information of cultivable β-glycosidase-producing Endophytic fungus in Panax ginseng. The strain GE 17-18 has potential to be applied on the preparation for minor ginsenoside C-K in pharmaceutical industry.

Topologic connection between 2-D layered structures and 3-D diamond structures for conventional semiconductors.

When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III–V, and II–VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain–low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side.

Strain-Controlled of Compressive/Tensile Ge Epilayers on Si by Electron Cyclotron Resonance Chemical Vapor Deposition

In this study, we use electron cyclotron resonance chemical vapor deposition to investigate the strain behavior in Ge epilayers grown on silicon at a low temperature of 220°C. The strain in the Ge epilayers is transformed from compressive (−0.567%) to tensile (0.15%) as the process pressure decreases and main coil current increases. This tensile strain is due to intrinsic stress in the Ge epilayers at high process pressure and low main coil current. Besides, the Ge atoms have higher kinetic energy and shorter mean free path at low process pressure and high main coil current, which causes atomic bombardment effect on the Ge surfaces frequently. Thus, the intrinsic stress in Ge epilayers become compressive. The absorption coefficient of tensile and compressive strain in Ge films are measured using a UV–VIS-NIR spectrophotometer. The results show the absorption coefficients of the tensile strain Ge epilayer has a redshift condition on the absorption edge compare with compressive strain Ge epilayers. Finally, the structure information of the Ge epilayers is identified by atomic force microscopy and transmission electron microscopy. This strain control technology is modulated by film growth parameter, which can adjust the Ge bandgap for the device requirement.

(Invited) Challenges to Nano-Scale Device World

We are facing dramatic challenges dealing with future nano-scale devices, including performance, power consumption, new materials, device integration, interconnects, ultimate technological processes and novel functionalities, needing disruptive approaches and inducing fundamental tradeoffs for future ICs and Nanosystems. This paper will review recent advances and promising solutions for future high performance and ultra low power devices including 2D layers, TMDs, heterostructures and quantum wells using strain Si, Ge and III-V thin films, multi-gates, nanowires, CNTs, tunnel FETs and NEMS.

Growth Studies of Doped SiGeSn/Strained Ge(Sn) Heterostructures

Large-scale integration of Si optoelectronics is still hampered due to the lack of efficient group IV light emitting materials. One promising way to overcome this obstacle is to introduce tensile strain in Ge in order to reduce the energy difference between the Γ- and the L-valley in the conduction band. A fully Si compatible technology for straining Ge becomes feasible by the use of large lattice constant strain relaxed (Si)GeSn buffer layers. Additionally, it has been theoretically shown that SiGeSn ternary alloys are ideal candidates as cladding layers in SiGeSn/sGe(Sn) heterostructures for photonic devices. In this contribution we present studies on (i) epitaxial strain engineering of SiGeSn alloys (to strain Ge) and (ii) the in-situ doping of such ternary compounds.The Sn-based heterostructures shown here have been grown by Reduced-Pressure Chemical Vapor Deposition (RP-CVD) using Si2H6, Ge2H6 and SnCl4. Low growth temperatures (350 – 400°C) have been employed to avoid Sn precipitation and obtain high substitutional Sn concentrations in 200-300 nm thick, partially strain relaxed (Si)GeSn buffer layers (SRB) for strained Ge (sGe). SiGeSn:P and SiGeSn:B layers grown in the same temperature range using B2H6 (100 ppm in H2) and undiluted PH3 precursors have been investigated by means of electrochemical C-V (ECV) profiling, sheet resistance measurements and ToF-SIMS.Fig. 1a shows the reciprocal space map (RSM) of 70 nm strained Ge grown on a 250 nm Ge0.89Sn0.11 SRB. This method allows an accurate determination of the in-plane and out-of-plane lattice constant of the GeSn SRBs and the overgrown sGe. The GeSn peak is obtained above the cubic lattice line indicating residual compressive strain. The degree of relaxation is about 73 %. Since the sGe peak lies on the pseudomorphic line of the SRB this top layer is tensile strained (1.4 %) coherently to the GeSn. The strain levels for several strained Ge layers grown on GeSn SRBs are summarized in Fig 1b. The strain level in overgrown sGe(Sn) layers can be adjusted by the choice of the Sn content and degree of relaxation of the buffer. In-situ doping is the method of choice to dope SiGeSn ternary layers due to the reduced thermal stability of Sn-based materials. The resistivity of SiGeSn:B and SiGeSn:P layers is shown in Fig. 1c as a function of the dopant partial pressure. The resistivity decreases for SiGeSn:B and increases for SiGeSn:P layers as the dopant partial pressure increases. In the latter case, a reduced layer quality has been found for PH3 partial pressures above 10 Pa indicated by an increase of the RBS/Channeling minimum yield, cmin (inset). The growth rates for doped ternaries do not show any dopant partial pressure dependence at least at a constant growth temperature of 425°C (inset). Interestingly, the growth rate for SiGeSn:P is higher than for SiGeSn:B layers which is comparable to that of undoped SiGeSn (44.5 nm/min). More B atoms are incorporated on substitutional lattice sites for high B2H6 partial pressures, leading to increased dopant activation up to 2x1019 cm-3 without dopant segregation. Within the investigated process window, the ECV profiling of a p-n junction with the highest achieved doping concentrations of 2x1019 cm-3 (p-type) and 8x1019 cm-3 (n-type) is shown in Fig. 1d. The very low Χmin of about 5 %, comparable to that of the Ge-VS underneath, indicates high single crystalline quality with high dopant substitutionality without Sn or P segregation.Fig. 1 (a) XRD-RSM of a highly (1.4 %) tensile strained Ge layer grown on a partially relaxed GeSn buffer layer. (b) 3d plot of several tensile strained Ge layers on differently alloyed GeSn layers. (c) Resistivity as a function of the dopant partial pressure for SiGeSn:B and SiGeSn:P layers. The minimum channeling yields and growth rates are shown in the insets. (d) ECV profile of a SiGeSn p-n junction. The RBS/Channeling spectra are shown in the inset.

Dependence of electronic properties of germanium on the in-plane biaxial tensile strains

The hybrid HSE06 functional with the spin–orbit coupling effects is used to calculate the habituation of the electronic properties of Ge on the (001), (111), (101) in-plane biaxial tensile strains (IPBTSs). Our motivation is to explore the nature of electronic properties of tensile-strained Ge on different substrate orientations. The calculated results demonstrate that one of the most effective and practical approaches for transforming Ge into a direct transition semiconductor is to introduce (001) IPBTS to Ge. At 2.3% (001) IPBTS, Ge becomes a direct bandgap semiconductor with 0.53eV band gap, in good agreement with the previous theoretical and experimental results. We find that the (111) and (101) IPBTSs are not efficient since the shear strain and inner displacement of atoms introduced by them quickly decrease the indirect gap of Ge. By investigating the dependence of valence band spin–orbit splitting on strain, we prove that the dependency relationship and the coupled ways between the valence-band states of tensile-strained Ge are closely related to the symmetry of strain tensor, i.e., the symmetry of the substrate orientation. The first- and second-order coefficients describing the dependence of indirect gap, direct gap, the valence band spin–orbit coupling splitting, and heavy-hole–light-hole splitting of Ge on IPBTSs have been obtained by the least squares polynomial fitting. These coefficients are significant to quantitatively modulate the electronic properties of Ge by tensile strain and design tensile-strained Ge devices by semiconductor epitaxial technique.

Experimental Investigation of Hole Transport in Strained $\hbox{Si}_{1 - x}\hbox{Ge}_{x}/\hbox{SOI}$ pMOSFETs—Part I: Scattering Mechanisms in Long-Channel Devices

This paper presents a wide experimental study of hole transport in SiGe pMOSFETs. Various Ge contents, from 20% up to 60%, and growth templates [unstrained or tensely strained silicon-on-insulator (SOI)] were screened in order to study the influence of various strain levels and Ge concentrations. Electrical results have been compared with the amount of strain in the channel, characterized through dark-field electron holography and nano-beam electron diffraction. The SiGe channel/oxide interface has been investigated through spectroscopic charge pumping and low temperature measurements. We found the signature of Ge-induced defects, particularly near the valence band. The different scattering mechanisms limiting the hole mobility in long-channel transistors have been decorrelated and discussed in the light of the different experimental data provided. We have shown in particular the low contribution of alloy scattering in the SiGe devices under study, and that carrier transport is dominated by the strain effect for Ge content up to 40%. The roughness parameters of the SiGe channel/oxide interface are also modified, with a less prejudicial impact on mobility. The effect of strain and Ge content on the different scattering mechanisms has been established. The combination of all the scattering contributions leads to a maximum mobility at room temperature for a Ge content <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ge</sub> = 0.4 on an SOI template, or equivalently, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ge</sub> = 0.6 on a strained SOI template.

Nanoscale concentration and strain distribution in pseudomorphic films Si1−xGex/Si processed by pulsed laser induced epitaxy

We report on the structural analysis of Si1−xGex pseudomorphic layers synthesized by pulsed laser induced epitaxy (PLIE) using a nanosecond excimer laser. We focus here on the local determination of strain and related Ge concentration. First, a Ge amorphous layer is predeposited on a Si substrate. Successive laser pulses induce the incorporation of Ge atoms in the molten substrate layer and lead to the synthesis of a graded Si1−xGex alloy over a depth which depends on the laser fluence. The Si1−xGex layers are coherently strained and free of defects. The in-depth Ge concentration distribution is investigated by RBS and HAADF STEM. The strain fields are specifically explored using the new dark-field electron holography (Holodark) technique, offering mapping of the full strain tensor in two dimensions with a high precision. Independently determined strain and Ge concentration distributions over a distance of 150nm from the surface are found to be well consistent. An unexpected but reproducible depletion of Ge is evidenced inside the SiGe layer. This feature is shown to be related to the shape of the temporal characteristics of laser pulses. In particular, the second contribution, which occurs 32ns later, is involved in a two-stage solidification process.

Critical Factors for Enhancement of Compressive Strain in SGOI Layers Fabricated by Ge Condensation Technique

SGOI layers with high compressive strain and high Ge content are promising channel materials for high current drive pMOSFETs under future technology nodes. In order to clarify the way of maximizing strain in SiGe-On-Insulator (SGOI) structures with high Ge fraction fabricated by th Ge condensation technique, we have examined the strain relaxation behaviors of the SGOI layers during the condensation process. The relationship among compressive strain in SGOI, the oxidation recipe and the substrate structures before oxidation has been quantitatively evaluated. With increasing the Ge fraction, the compressive strain in the SGOI layers linearly increases in lower Ge contents and rapidly decreases after it reaches peak values. It is found that the higher oxidation temperature and the Ge content in the SiGe epitaxial layers before oxidation are influential factors in mitigating the strain relaxation, in addition to the use of the strained Si-On-Insulator (sSOI) substrates As a result of optimizing these structural parameters, we have successfully obtained SGOI with 2.5% compressive strain under the Ge content of 0.86.

Impact of Strain or Ge Content on the Threshold Voltage of Nanoscale Strained-Si/SiGe Bulk MOSFETs

The impact of strain on the threshold voltage of nanoscale strained-Si/SiGe MOSFETs is studied by developing a compact analytical model. Our model includes the effects of strain (Ge mole fraction in SiGe substrate), short-channel length, source/drain junction depths, substrate (body) doping, strained silicon thin-film thickness, gate work function, and other device parameters. The model correctly predicts a decrease in threshold voltage with increasing strain in the silicon thin film, i.e., with increasing Ge concentration in SiGe substrate. The accuracy of the results obtained using our analytical model is verified using two-dimensional device simulations.

Compact Analytical Threshold-Voltage Model of Nanoscale Fully Depleted Strained-Si on Silicon–Germanium-on-Insu lator (SGOI) MOSFETs

In this paper, a physically based analytical threshold-voltage model is developed for nanoscale strained-Si on silicon-germanium-on-insulator MOSFETs for the first time, taking into account short-channel effects. The model is derived by solving the 2-D Poisson equation in strained-Si and SiGe layers. The effects of various important device parameters like strain (Ge mole fraction in the SiGe layer), body doping, gate workfunction, strained-Si thin film and SiGe layer thickness, etc., has been considered. We have demonstrated that increasing strain in order to enhance device performance can lead to undesirable threshold-voltage rolloff. The model is found to agree well with the 2-D simulation results

Thermal stability of strained Si/Si 1− xGe x heterostructures for advanced microelectronics devices

The thermal stability of strained Si/Si 1− x Ge x epilayers with x=0.15 to 0.25 was investigated under various thermal annealing conditions. High Resolution (HR) X-ray Diffractometry (XRD) was used to determine the intrinsic strain of the heterostructure before any thermal treatment. The effect of thermal processing on strain relaxation and Ge diffusion was observed by Raman spectroscopy and Secondary Ion Mass Spectroscopy (SIMS). Strain analysis by Raman reveals no sign of Si strain relaxation for temperatures up to 1000 °C for 5 min. However, Ge diffusion into strained Si was detected by both Raman and SIMS.

Annealing studies of high Ge composition Si/SiGe multilayers

Abstract For the design flexibility of SiGe based quantum cascade lasers high Ge composition Si/SiGe (x = 80%) superlattices are important. We present an X-ray small angle scattering and high-resolution X-ray diffraction study on strain compensated Si/Si1– x Gex multiple quantum well structures with Ge compositions (x up to 80%), grown on Si0.5Ge0.5 pseudo-substrates. To test the temperature stability of such layers occurring in processing steps, in-situ annealing X-ray reflectivity measurements were performed for temperatures up to 810 °C. From the analysis of the reflectivity data, we obtain the layer thicknesses and the interface roughness of the superlattices during annealing. Using a one dimensional diffusion equation, the Ge diffusion coefficient for these conditions was obtained. Furthermore, the strain status and Ge composition in the superlattice structure and in the SiGe buffer before and after annealing were determined from the symmetrical and asymmetrical reciprocal space maps.

Biotransformations of cinnamic and ferulic acid with actinomycetes

Biotransformations of cinnamic and ferulic acid catalysed by actinomycetes have been studied. A primary screening was carried out using 535 actinomycetes isolated from soil and able to grow in the presence of cinnamic (500) or ferulic acid (35). A mininiaturized procedure of biotransformation in solid medium showed that, among the strains able to metabolise the substrates, the more frequent behaviours were the degradation of cinnamic acid (often via benzoic acid formation) or transformation in cinnamamide (22 strains), while ferulic acid was mostly degraded with transient accumulation of vanillic acid in few cases. A more restricted screening (57 representative strains) was carried out in submerged cultures: strain GE 107678, identified as Streptomyces halstedii, converted cinnamic acid in cinnamamide (95% molar conversion from 2 g/l of substrate) and ferulic acid in vanillic acid (80% molar conversion from 1 g/l of substrate) with transient formation of low amounts of vanillin (0.10–0.15 g/l).