We report on the properties of p-type delta-doped layers prepared in molecular beam epitaxy-Si by growth interruption and evaporation of elemental B. Secondary-ion mass spectrometry measurements at several primary ion energies have been... more
We report on the properties of p-type delta-doped layers prepared in molecular beam epitaxy-Si by growth interruption and evaporation of elemental B. Secondary-ion mass spectrometry measurements at several primary ion energies have been used to show that the full width at half maximum is ∼2 nm. Hall measurements confirm that the layers are completely activated at 300 K with a mobility of 30±5 cm2/V s for a carrier density of (9±2)×1012 cm−2. At temperatures below 70 K nonmetallic behavior is observed which we have attributed to conduction between impurity states. It is concluded that the critical acceptor separation for the Mott metal-insulator transition in this system is significantly less than the value found in uniformly doped Si:B.
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ABSTRACTA dedicated, grower-friendly MBE computer control system is described, and its performance in demonstrated in growth of high resolution doped SiGe structures.
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With its higher carrier mobilities and lower effective masses than silicon, germanium is a potential channel replacement material for future CMOS. Using data obtained from high performance Ge pMOSFETs with gate lengths down to 125 nm, we... more
With its higher carrier mobilities and lower effective masses than silicon, germanium is a potential channel replacement material for future CMOS. Using data obtained from high performance Ge pMOSFETs with gate lengths down to 125 nm, we deduce values for the backscattering coefficient and ballisticity for temperatures in the range from 300 K to 4 K. We find there is
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Research Interests: Physics, Condensed Matter Physics, Silicon, Medicine, Germanium, and 4 morePhysical, Voltage, QC, and Coulomb blockade
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... Mod. Phys. 54 Asche M , Friedland K J, Kleinert P, Kostial H, Herzog J and Bishop D J, Dynes RC and Tsui D C 1982 Phys. Rev. B 26 Phys. ... lwahuchi S and Nagaoka Y 1989 J. Phys. Soc. Japan 58 1325 Kearney M J and Butcher P N I988 J.... more
... Mod. Phys. 54 Asche M , Friedland K J, Kleinert P, Kostial H, Herzog J and Bishop D J, Dynes RC and Tsui D C 1982 Phys. Rev. B 26 Phys. ... lwahuchi S and Nagaoka Y 1989 J. Phys. Soc. Japan 58 1325 Kearney M J and Butcher P N I988 J. Phys. C: Solid State Phys. ...
Research Interests: Materials Engineering, Mathematical Physics, Condensed Matter Physics, Chemistry, Silicon, and 15 moreDoping, Magnetic field, Low Temperature Physics, Inelastic Neutron Scattering, Boron, Ta, Temperature Dependence, Science Technology, Scattering, Tk, QC, Interaction effect, Low Temperature, Hall effect, and Sheet Resistance
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In this paper, we present a transmission electron microscopy analysis of novel Ge-on-Si MOSFETs using a JEOL 2010F and an aberration-corrected JEOL 2200FSC. A key feature of these devices is the incorporation of a very thin (~1nm) Si... more
In this paper, we present a transmission electron microscopy analysis of novel Ge-on-Si MOSFETs using a JEOL 2010F and an aberration-corrected JEOL 2200FSC. A key feature of these devices is the incorporation of a very thin (~1nm) Si passivation layer on top of the Ge virtual substrate, which is partially oxidised to form SiO2 (~0.5nm) prior to depositing HfO2 dielectric. We will show that the thin SiO2 layer is not purely amorphous but has some degree of crystal ordering due to being bonded to crystalline materials. Moreover, we will examine the presence of small monolayer variation in Si/SiO2 interface roughness.
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Abstract Quantum dots of 50~ 60 nm diameter fabricated from both Si/Si 1-x Ge x (x= 0.1~ 0.3) strained layer superlattices and a strain symmetried Si 9/Ge 6 superlattice were investigated by a combination of Raman scattering,... more
Abstract Quantum dots of 50~ 60 nm diameter fabricated from both Si/Si 1-x Ge x (x= 0.1~ 0.3) strained layer superlattices and a strain symmetried Si 9/Ge 6 superlattice were investigated by a combination of Raman scattering, photoluminescence, and ...
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... A33 (1977) 137. 1021 0.1 Depth (microns) AR. Powell et aL / Elemental B and Sb doping of MBE Si and SiGe structures 911 [10] NL Mattey, M. Hopkinson, RF Houghton, MG Dowsett, TE Whall, EHC Parker, GR Booker and J. Whitehurst, Thin... more
... A33 (1977) 137. 1021 0.1 Depth (microns) AR. Powell et aL / Elemental B and Sb doping of MBE Si and SiGe structures 911 [10] NL Mattey, M. Hopkinson, RF Houghton, MG Dowsett, TE Whall, EHC Parker, GR Booker and J. Whitehurst, Thin Solid Films 15 (1990) 184. ...
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The formation of buried SiO2 layer by high-dose oxygen implanted into Si/Ge and Si/Si0.5Ge0.5 heterostructures is studied by infrared transmission and x-ray photoelectron spectroscopy. The results show that the Ge in the implanted region... more
The formation of buried SiO2 layer by high-dose oxygen implanted into Si/Ge and Si/Si0.5Ge0.5 heterostructures is studied by infrared transmission and x-ray photoelectron spectroscopy. The results show that the Ge in the implanted region has no influence on the bonding properties of oxygen, and there exists a critical annealing temperature of about 1250 °C for all the implanted oxygen to
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Research Interests: Engineering, Physics, Materials Science, Kinetics, Transmission Electron Microscopy, and 10 moreOptoelectronics, Physical sciences, Electrical Properties, Tk, QC, Low Temperature, Positron Annihilation Spectroscopy, Field effect transistor, Metal Oxide Semiconductor Field Effect Transistor, and Point Defect
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Research Interests: Engineering, Materials Science, Chemistry, Quantum Optics, Applied Physics, and 15 moreNear Infrared, Photoluminescence, Molecular beam epitaxy, Optoelectronics, Quantum Confinement, Physical sciences, Spontaneous Emission, Quantum Dot, QC, Epitaxy, Quantum Well, Porous Material, Exciton, Amorphous Silicon, and Anodizing
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The electrical conductivity of the 2DHG formed at the 0268-1242/12/10/009/img2 interface has been measured on samples with composition 0.05<x<0.29 and carrier sheet densities between 0268-1242/12/10/009/img3 and... more
The electrical conductivity of the 2DHG formed at the 0268-1242/12/10/009/img2 interface has been measured on samples with composition 0.05<x<0.29 and carrier sheet densities between 0268-1242/12/10/009/img3 and 0268-1242/12/10/009/img4 in the temperature range 0.3 K to 1.6 K. It is found that the temperature (T) dependence is described by the superposition of a screening term linear in T and a logarithmic term associated with weak localization and carrier - carrier interactions. We find no evidence for a screening term with a 0268-1242/12/10/009/img5 dependence as has been predicted as a consequence of lifetime broadening. The results are in satisfactory quantitative agreement with Gold and Dolgopolov's theory of screening of short-range scattering centres.
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For the first time, we have demonstrated the reduced low-frequency (LF) noise in sub-μm metamorphic high Ge content p-Si0.3Ge0.7 MOSFETs in comparison with p-Si MOSFETs at 293K. Three times lower LF noise over 1–100Hz range at VDS=−50mV... more
For the first time, we have demonstrated the reduced low-frequency (LF) noise in sub-μm metamorphic high Ge content p-Si0.3Ge0.7 MOSFETs in comparison with p-Si MOSFETs at 293K. Three times lower LF noise over 1–100Hz range at VDS=−50mV and VG−VTH=−1.5V was measured for the 0.55μm effective gate length p-Si0.3Ge0.7 MOSFET compared with p-Si MOSFET. Over three times drain current enhancement in
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We describe a high sensitivity THz detector based on the hot electron effect in a highly doped thin silicon semiconducting layer with tunnelling contacts to superconducting islands (S-Sm-S).
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Page 1. Low Temperature Performance of Deep Submicron Germanium pMOSFETs Andy Dobbie'. Gareth Nicholas2. Marc Meuris2. Evan HC Parker' and Terry E. Whall' INano-Silicon Group, Dept. of Physics, University of Warwick,... more
Page 1. Low Temperature Performance of Deep Submicron Germanium pMOSFETs Andy Dobbie'. Gareth Nicholas2. Marc Meuris2. Evan HC Parker' and Terry E. Whall' INano-Silicon Group, Dept. of Physics, University of Warwick, Coventry, CV4 7AL, UK ...
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ABSTRACT In this work, we report a hole mobility of one million in germanium. This extremely high value of 1.1 x 106 cm2V-1s-1 at a carrier sheet density of 3.0 x 1011 cm-2 was observed in a strained Ge quantum well structure grown by... more
ABSTRACT In this work, we report a hole mobility of one million in germanium. This extremely high value of 1.1 x 106 cm2V-1s-1 at a carrier sheet density of 3.0 x 1011 cm-2 was observed in a strained Ge quantum well structure grown by reduced-pressure chemical vapor deposition (RP-CVD) and is nearly an order of magnitude higher than previously reported values [1]. Compressively strained Ge offers considerable promise as an alternative channel conduction material to Si because of its previously reported high hole mobility of 120,000 cm2V-1s-1 (at 2 K) [1] in two-dimensional hole gases (2DHG) in modulation-doped SiGe heterostructures [2-4]. Previous studies have used growth techniques such as molecular beam epitaxy (MBE) and low energy plasma enhanced chemical vapor deposition (LEPE-CVD), or a combination of these techniques to take advantage of their low growth rates for accurate control of the epitaxial layer properties. However, recent developments in low temperature epitaxy using reduced-pressure CVD (RP-CVD) now makes it possible using an industrially compatible process to control the thickness of strained epitaxial layers to within a few monolayers [5] and achieve very high levels of purity. The heterostructure studied in this work is shown in Fig. 1. All layers were grown by reduced pressure CVD (RP-CVD) using an ASM Epsilon 2000 reactor and employed a reverse-linearly graded Si0.2Ge0.8 relaxed buffer with low surface roughness (rms value ~ 2 nm, crosshatch spatial wavelength ~ 2 m) and threading dislocation density (≤ 4 x 106 cm-2) [6-7]. The active region included a 20 nm biaxial compressively strained Ge QW, that was grown at low temperature to prevent any relaxation [8]. High resolution x-ray diffraction (HR-XRD) confirmed that the Si0.2Ge0.8 buffer was slightly over-relaxed with respect to the Si substrate and that the Ge channel was fully strained with respect to the buffer. The B-doping density was determined as ~ 1 x 1018 cm-3 using ultra low energy secondary ion mass spectrometry (uleSIMS). Hall bars were fabricated using standard lithography and wet chemical etching while Al contacts were deposited by thermal evaporation and annealed at 425 °C for 20 mins in N2 to ensure ohmic behavior. Resistivity and Hall effect measurements were performed in the temperature range 12 K - 300 K with Fig. 2 showing the Hall mobility and carrier sheet density as a function of temperature. The room temperature Hall mobility was 1200 cm2V-1s-1 and is believed to be dominated by parallel conduction through the MOD heterostructure [2]. However, at 12 K the measured Hall mobility and carrier sheet density were 1.0 x 106 cm2V-1s-1 and 3.0 x 1011 cm-2, respectively and represents the highest hole mobility observed for a 2DHG in strained Ge. Fig. 2 shows that whilst the carrier sheet density saturates, the Hall mobility continues to increase for temperatures below 60 K. Additional experiments at 0.4 K found that the Hall mobility saturated at a value of ~ 1.1 x 106 cm2V-1s-1. At low temperatures, we expect the mobility to be limited by ionized impurity scattering [1]. Our results suggest that the RP-CVD growth process has resulted in both a very low impurity and extremely pure Ge layer, so that even at 12 K ionized impurity scattering is very weak [9] and demonstrates that RP-CVD can be used to grow strained Ge QWs with exceptionally high hole mobilities.
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Page 1. Simple fabrication of suspended Germanium structures and their electrical properties from high quality Ge on Si(001) layers. Vishal A. Shah, Maksym Myronov, Chalermwat Wongwanitwatana, Richard JH Morris, Martin ...
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ABSTRACT The influence of the method of series resistance determination on the extracted channel mobility is investigated in MOS transistors with relaxed and strained Ge channel. The dependence of the extracted mobility on the channel... more
ABSTRACT The influence of the method of series resistance determination on the extracted channel mobility is investigated in MOS transistors with relaxed and strained Ge channel. The dependence of the extracted mobility on the channel length and the frequency of the signal used to measure capacitance-voltage characteristics are examined.
ABSTRACTSilicon germanium pMOSFETs with channel lengths down to 0.4m have been fabricated on limited area silicon germanium virtual substrates. The devices have a 5nm thick Si0.3Ge0.7 active layer grown by MBE on top of relaxed Si0.7Ge0.3... more
ABSTRACTSilicon germanium pMOSFETs with channel lengths down to 0.4m have been fabricated on limited area silicon germanium virtual substrates. The devices have a 5nm thick Si0.3Ge0.7 active layer grown by MBE on top of relaxed Si0.7Ge0.3 virtual substrate. Virtual substrates were grown on top of 10μm square silicon pillars defined by etching trenches around their perimeter into the original silicon substrate. This limits the area of the growth zone, which in turn promotes the relaxation of the virtual substrate. Electrical measurements on 2μm long channel devices show that the maximum mobility in the strained SiGe devices is 211cm2V-1cm-1, compared to 104cm2V-1cm-1 for silicon reference devices. This increase in hole mobility increases the current drive of 0.4m devices measured at Vgt=-2V, Vds=-2.5V from 154μA/m to 192μA/μm.
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ABSTRACTIn MBE Si1−xGex which is grown to thicknesses greater than the critical thickness hc, the dislocation-related luminescence peaks Dl and D2 have energies which are independent of x up to x ≈ 0.3, and then decrease, as observed in... more
ABSTRACTIn MBE Si1−xGex which is grown to thicknesses greater than the critical thickness hc, the dislocation-related luminescence peaks Dl and D2 have energies which are independent of x up to x ≈ 0.3, and then decrease, as observed in LPE Si1−xGex. In MBE Si1−xGex layers grown to thicknesses less than hc, post-growth annealing produces dramatic changes in the luminescence, giving spectra as from relaxed alloy, even though the relaxation determined by X-rays is negligible. These results establish photoluminescence as a sensitive diagnostic tool for detecting dislocations in Si1−xGe*.
Cyclotron resonance (CR) has been used to measure the effective mass of holes in a series of p-type modulation doped Si1-xGex/Si heterostructures, in which x varies from 0.05 to 0.29, and the two-dimensional carrier density... more
Cyclotron resonance (CR) has been used to measure the effective mass of holes in a series of p-type modulation doped Si1-xGex/Si heterostructures, in which x varies from 0.05 to 0.29, and the two-dimensional carrier density ps=(0.95-5.8)×1011 cm-2. The measured masses for these samples are, to the best of our knowledge, the lowest yet reported, with a mass as low as
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ABSTRACT This chapter presents some recent advances in the field of thermal energy harvesting, starting with thermoelectric energy harvesting, with a focus on the prospects of materials nanostructuration. Research toward alternative... more
ABSTRACT This chapter presents some recent advances in the field of thermal energy harvesting, starting with thermoelectric energy harvesting, with a focus on the prospects of materials nanostructuration. Research toward alternative solutions will also be presented. Thermoelectric (TE) conversion is the most straightforward method to convert thermal energy into electrical energy, able to power such systems as autonomous sensor networks. Raman thermometry offers particular advantages for a fast and contactless determination of the thermal conductivity. The highly porous Si material is nanostructured and has the properties of confined systems, including a very low thermal conductivity. The chapter explores an alternative route for thermal energy harvesting (TEH) with composites using the mechanical coupling between a thermal shape memory alloy (SMA) and a piezoelectric material.