1,592,858 research outputs found
Transport properties for pure strained Ge quantum well
No full textModulation doped heterostructures consisting of a strained Ge (sGe) quantum well on a Si0.2Ge0.8 virtual substrate have been used to study enhancement of the transport properties of holes in the sGe channel due to the effective reduction of impurity scattering by placing the doping layer away from the channel.
Electrical and structural analysis was performed for sGe heterostructures produced with a range of growth parameters. The highest hole mobility was 1.34×106 cm2 /Vs at 0.5 K for a sGe quantum well in a 'normal' structure (i.e. doped above the channel) at a sheet density of 2.9×1011 cm-2, which is the largest hole mobility reported in Ge to date. 'Inverted' structures (doping layer under the channel) were also studied for different sample parameters such as channel thickness, spacer thickness, doping and different temperature growth, with a hole
mobility as high as 5.08×105 cm2 /Vs at a sheet density of 5.14×1011 cm-2 at 90 mK.
Simulations of the scattering limited mobility for inverted and normal structures were performed and showed that at low sheet density background impurity scattering limits the low temperature hole mobility. However, as the sheet density increases interface roughness scattering becomes the mobility limiting process, especially in the case of inverted structures where the resistivity and mobility anisotropy is more pronounced.
Magnetotransport measurements revealed the lowest reported effective mass for holes in Ge of 0.063±0.001 m0 for the normal structure and 0.07±0.002 m0 & 0.063±0.003 m0 for two inverted structures, and highest Dingle factors of α=78 and 33 for the normal and inverted structures, respectively. The low level of background impurities, high structural quality, and pure Ge channel revealed by structure characterisation are believed to be responsible for these exceptionally high values of mobility
Observation of negative differential conductance in a reverse-biased Ni/Ge Schottky diode
No full textWe report the experimental observation of negative differential conductance in a Ni/Ge Schottky diode. With the aid of theoretical models and numerical simulation we show that, at reverse bias, electons tunnel into the high electric field of the depletion region. This scatters the electrons into the upper valley of the Ge conduction band, which has a lower mobility. The observed negative differential conductance is hence attributed to the transferred-electron effect. This shows that Schottky contacts can be used to create hot electrons for transferred-electron devices
Fabrication and characterisation of novel Ge MOSFETs
No full textAs high-k dielectrics are introduced into commercial Si CMOS (Complimentary Metal Oxide Semiconductor) microelectronics, the 40 year channel/dielectric partnership of Si/SiO2 is ended and the door opened for silicon to be replaced as the active channel material in MOSFETs (Metal Oxide Semiconductor Field Effect Transistor). Germanium is a good candidate as it has higher bulk carrier mobilities than silicon. In addition, Si and Ge form a thermodynamically stable SiGe alloy of any composition, allowing Ge to be implemented as a thin layer on the surface of a standard Si substrate. This thesis is a practical investigation on several aspects of Ge CMOS technology.
High-k dielectric Ge p-MOSFETs are electrically characterised. A large variation in interface state densities is demonstrated to be responsible for a threshold voltage shift and this is proportional to reciprocal peak mobility due to the Coulomb scattering of carriers by charged states. A theoretical mobility is fitted to that measured at 4.2 K and confirms that interface states are the main source of interface charged impurities.
The model demonstrates a reduction in the interface charged impurity density in p-MOSFETs that underwent a PMA (Post Metallisation Anneal) in hydrogen atmosphere and that the anneal also reduces the RMS (Root Mean Square) dielectric/semiconductor interface roughness, from an average of 0.60 nm to 0.48 nm.
High-k strained Ge p-MOSFETs are electrically characterised and have peak mobilities at 300 K (470 cm2 V-1 s-1) and 4.2 K (1780 cm2 V-1 s-1) far in excess of those measured for the unstrained Ge p-MOSFETs (285 cm2 V-1 s-1,785 cm2 V-1 s-1 respectively). Strained Ge n-MOSFETs perform significantly worse than standard Si P, - MOSFETs primarily due to a high source/drain resistance.
A 10 nm thick SiGe-01 (On Insulator) layer with a Ge composition of 58% is obtained from a 55 nm Si0_88Ge1o2. initial layer on 100 nm Si-Ol substrate via the germanium condensation technique. For the first time, germanium is demonstrated to diffuse through the BOX (Buried OXide) during Ge-condensation and into the underlying Si substrate. An order of magnitude increase in the calculated ITOX (Internal Thermal OXidation) rate of the BOX in the final stages of Ge-condensation is hypothesised to be responsible for stopping this diffusion
Ge-conservación Nº26
No full textGe-conservación es una publicación periódica del GEIIC, cuyo objetivo es contribuir al desarrollo científico, a la difusión y al intercambio de los conocimientos en materia de conservación y restauración del Patrimonio Cultural
Synthesis, structure, and properties of [nacnac]MX3 compounds (M = Ge, Sn; X = Cl, Br, I)
No full textReactions of [nacnac]Li [(2,6-(Pr2C6H3)-Pr-i)NC(Me) C(H)C(Me)N(2,6-(Pr2C6H3)-Pr-i)]Li (1) with SnX4 (X = Cl, Br, I) and GeCl4 in Et2O resulted in metallacyclic compounds with different structural moieties. In the [nacnac]SnX3 compounds (X = Cl 2, Br 3, 1 4) the tin atom is five coordinated and part of a six membered ring. The Sn-N-bond length of 3 is 2.163(4)Angstrom and 2.176(5) Angstrom of 4. The five coordinated germanium of the [nacnac]GeCl3 compound 5 shows in addition to the three chlorine atoms further bonds to a carbon and to a nitrogen atom. In contrast to the known compounds with the [nacnac] ligand the afore mentioned reaction creates a carbon-metal-bond (1.971(3)Angstrom) forming a four-membered ring. The Ge-N bond length (2.319(2) Angstrom) indicates the formation of a weakly coordinating bond
Synthesis, structure, and properties of [nacnac]MX3 compounds (M = Ge, Sn; X = Cl, Br, I)
No full textReactions of [nacnac]Li [(2,6-(Pr2C6H3)-Pr-i)NC(Me) C(H)C(Me)N(2,6-(Pr2C6H3)-Pr-i)]Li (1) with SnX4 (X = Cl, Br, I) and GeCl4 in Et2O resulted in metallacyclic compounds with different structural moieties. In the [nacnac]SnX3 compounds (X = Cl 2, Br 3, 1 4) the tin atom is five coordinated and part of a six membered ring. The Sn-N-bond length of 3 is 2.163(4)Angstrom and 2.176(5) Angstrom of 4. The five coordinated germanium of the [nacnac]GeCl3 compound 5 shows in addition to the three chlorine atoms further bonds to a carbon and to a nitrogen atom. In contrast to the known compounds with the [nacnac] ligand the afore mentioned reaction creates a carbon-metal-bond (1.971(3)Angstrom) forming a four-membered ring. The Ge-N bond length (2.319(2) Angstrom) indicates the formation of a weakly coordinating bond
H-Bridged Structures for Tetrahedranes A<sub>4</sub>H<sub>4</sub> (A = C, Si, Ge, Sn, and Pb)
No full textAb initio MO studies at the HF, MP2, and
Becke3LYP levels on H-bridged tetrahedranes of the group
14
elements (A4H4, A = C, Si, Ge, Sn, Pb) with
the 6-31G* basis set for C and Si and LANL1DZ and
quasirelativistic
pseudopotential basis sets for Ge, Sn, and Pb are reported. As
expected, the classical Td structure
1 is more stable
than all the other tetrahedrane alternatives for
C4H4. The triply hydrogen bridged
structure 2
(C3v) is found to
be
more stable for Si, Ge, and Sn. Pb4H4
prefers the four H-bridged structure 8
(Cs). However, the calculations
with
the quasirelativistic pseudopotential basis set show the quadruply
H-bridged D2d structure
7 to be the most stable
structure for Ge, Sn, and Pb. Thus the structures derived from the
transition metal organometallic chemistry are
competitive for heavier elements (Si to Pb). The periodic behavior
begins only with the second period; Li to Ne, are
the exceptions. Suggestions for the realization of these H-bridged
structures for Pb from NaPb are discussed
Electrodeposited Ni/Ge and germanide schottky barriers for nanoelectronics applications
No full textIn recent years metal/semiconductor Schottky barriers have found numerous applications in nanoelectronics. The work presented in this thesis focuses on the improvement of a few of the relevant devices using electrodeposition of metal on Ge for Schottky barrier fabrication. This low energy metallisation technique offers numerous advantages over the physical vapour deposition techniques. Electrical characteristics of the grown diodes show a high quality rectifying behaviour with extremely low leakage currents even on highly doped Ge. A non-Arrhenius behaviour of the temperature dependence is observed for the grown Ni/Ge diodes on lowly doped Ge that is explained by a spatial variation of the barrier heights. The inhomogeneity of the barrier hights is explained in line with an intrinsic surface states model for Ge. The understanding of the intrinsic surface states will help to create ohmic contacts for doped n-MOSFETs. NiGe were formed single phase by annealing. Results reveal that by using these high-quality germanide Schottky barriers as the source/drain, the subthreshold leakage currents of a Schottky barrier MOSFET could be minimised, in particular, due to the very low drain/body junction leakage current exhibited by the electrodeposited diodes. The Ni/Ge diodes on highly doped Ge show negative differential conductance at low temperature. This effect is attributed to the intervalley electron transfer in Ge conduction band to a low mobility valley. The results show experimentally that Schottky junctions could be used for hot electron injection in transferred-electron devices. A vertical Co/Ni/Si structure has been fabricated for spin injection and detection in Si. It is shown that the system functions electrically well although no magnetoresistance indicative of spin injection was observed
Laser-vibrometric ultrasonic characterization of resonant modes and quality factors of Ge membranes
No full textThe vibrations of a single-crystal germanium (Ge) membrane are studied in air and vacuum using laser vibrometry, in order to determine mechanical properties such as Q-factors, tensile stress, anisotropy, and robustness to shock. Resonance modes up to 3:2 are identified, giving a residual stress measurement of 0.22 GPa, consistent with the value obtained from x-ray relaxation studies. The membrane is found to be isotropic, with Q-factors ranging from around 40 at atmospheric pressure to over 3200 at 5 x 10-4 mbar, significantly lower than those found in polycrystalline Ge micromechanical devices. The robustness to shock is explained through the high resonance mode frequencies and the dissipation mechanism into the substrate, which is a direct consequence of having a high quality film with low residual tensile stress, giving the potential for such films to be used in optoelectronic devices
Mechanism of vertical Ge nanowire nucleation on Si (111) during subeutectic annealing and growth
No full textThe direct integration of Ge nanowires with silicon is of interest in multiple applications. In this work, we describe the growth of high-quality, vertically oriented Ge nanowires on Si (111) substrates utilizing a completely sub-Au-Si-eutectic annealing and growth procedure. With all other conditions remaining identical, annealing below the Au-Si eutectic results in successful heteroepitaxial nucleation and growth of Ge nanowires on Si substrate while annealing above the Au-Si eutectic leads to randomly oriented growth. A model is presented to elucidate the effect of the annealing temperature, in which we hypothesized that sub-Au-Si-eutectic annealing leads to the formation of a single and well-oriented interface, essential to template heteroepitaxial nucleation. These results are critically dependent on substrate preparation and lead to the creation of integrated nanowire systems with a low thermal budget process
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