95,786 research outputs found
High quality Schottky contacts for limiting leakage currents in Ge-based Schottky barrier MOSFETs
No full textSchottky barrier (SB) Ge channel MOSFETs suffer from high drain-body leakage at the required elevated substrate doping concentrations to suppress source-drain leakage. Here we show that electrodeposited Ni-Ge and NiGe/Ge Schottky diodes on highly doped Ge show low off current, which might make them suitable for SB p-MOSFETs. The Schottky diodes showed rectification of up to 5 orders in magnitude. At low forward biases the overlap of the forward current density curves for the as deposited Ni/n-Ge and NiGe/n-Ge Schottky diodes indicates Fermi-level pinning in the Ge band gap. The SB height for electrons remains virtually constant at 0.52 eV (indicating a hole barrier height of 0.14 eV) under various annealing temperatures. The series resistance decreases with increasing annealing temperature in agreement with four point probe measurements indicating the lower specific resistance of NiGe as compared to Ni, which is crucial for high drive current in SB p-MOSFETs. We show by numerical simulation that by incorporating such high quality Schottky diodes in the source/drain of a Ge channel PMOS, highly doped substrate could be used to minimize the subthreshold source to drain leakage current
Anharmonic vibrational spectroscopy of germanium-containing clusters, Ge(x)C(4−x) and Ge(x)Si(4−x) (x = 0-4), for interstellar detection
No full textAn extensive, high-level theoretical study on tetra-atomic germanium carbide/silicide clusters is presented. Accurate harmonic and anharmonic vibrational frequencies and rotational constants are calculated at the CCSD(T)-F12a(b)/cc-pVT(Q)Z-F12 levels of theory. With growing capabilities to discern more of the chemical composition of the interstellar medium (ISM), an accurate database of reference material is required. The presence of carbon is ubiquitous in the ISM, and silicon is known to be present in interstellar dust grains, however germanium-containing molecules remain elusive. To begin understanding the presence and role of germanium in the ISM, we present this study of the vibrational and rotational spectroscopic properties of various germanium- containing molecules to aid in their potential identification in the ISM with modern observational tools such as the James Webb Space Telescope. Structures studied herein include rhomboidal (r-), diamond (d-), and trapezoidal (t-) tetra-atomic molecules of the form Ge(x)C(4−x) and Ge(x)Si(4−x) , where x=0-4. The most promising structure for detection is r-Ge(2)C(2) via the ν4 mode with a frequency of 802.7 cm−1 (12.5 μm) and an intensity of 307.2 km mol−1. Other molecules potentially detectable, i.e., through vibrational modes or rotational transitions, include r-Ge(3)C, r-GeSi(3), d-GeC(3), r-GeC(3), and t-Ge(2)C(2)
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
Strain-relaxed, high Ge content, SiGe layers grown on Si (100) substrate by reduced pressure - chemical vapour deposition (RP-CVD)
No full textA different approach was taken to relieve strain from a high Germanium (Ge) content,
Silicon-Germanium (SiGe) layers on a Silicon (Si) (100) substrate by growing a thin Ge
under-layer between substrate and layer. The Ge under-layer acts as a strain reliving platform
for further growth of a high Ge content SiGe layer to improve the structural quality of the
sample by reducing the Root Mean Squared Roughness (RRMS) and threading dislocation density
(TDD).
The proposed structure involves the growth of thin Si0.3Ge0.7 and Si0.5Ge0.95 buffer layers of
an average thickness of 350 nm grown on a Si (100) substrate and their structural qualities
assessed. Experimental techniques include High Resolution X-Ray Diffraction, Atomic Force
Microscopy, Transmission Electron Microscopy, and Defect Etching. All samples were
shown to be fully relaxed and have a surface roughness between 1-8 nm. However, a
threading dislocation density of 109 cm-2 was witnessed. Although these results are the first of
their kind, further research into improving structural qualities is to be investigated in the
future
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
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
Strained and strain-relaxed epitaxial Ge(1-x)Sn(x) alloys on Si(100) substrates
No full textEpitaxial Ge(1-x)Sn(x) alloys are grown separately on a Ge-buffer/Si(100) substrate and directly on a Si(100)subs trate by molecular beam epitaxy (MBE) at low temperature. In the case of the Ge buffer/Si(100)substrate, a high crystalline quality strained Ge(0.97)Sn(0.03) alloy is grown, with a chi(min) value of 6.7% measured by channeling and random Rutherford backscattering spectrometry (RBS), and a surface root-mean-square (RMS) roughness of 1.568 nm obtained by atomic force microscopy (AFM). In the case of the Si(100)substrate, strain-relaxed Ge(0.97)Sn(0.03) alloys are epitaxially grown at 150 degrees C-300 degrees C, with the degree of strain relaxation being more than 96%. The X-ray diffraction (XRD) and AFM measurements demonstrate that the alloys each have a good crystallin equality and a relatively flat surface. The predominant defects accommodating the large misfit are Lomer edge dislocations at the interface,which are parallel to the interface plane and should not degrade electrical properties and device performance
Growth and properties of magnetron cosputtering grown Mn(x)Ge(1-x)on Si(001)
No full textWe have grown MnxGe1-x films (x=0, 0.06, 0.1) on Si (001) substrates by magnetron cosputtering, and have explored the resulting structural, morphological, electrical and magnetic properties. X-ray diffraction results show there is no secondary phase except Ge in the Mn0.06Ge0.94 film while new phase appears in the Mn0.1Ge0.9 film. Nanocrystals are formed in the Mn0.06Ge0.94 film, determined by field-emission scanning electron microscopy. Hall measurement indicates that the Mn0.06Ge0.94 film is p-type semiconductor and hole carrier concentration is 6.07 X 10(19) cm(-3) while the MnxGe1-x films with x=0 has n-type carriers. The field dependence of magnetization was measured using alternating gradient magnetometer, and it has been indicated that the Mn0.06Ge0.94 film is ferromagnetic at room temperature. (c) 2005 Elsevier Ltd. All rights reserved
Efficient stepwise carrier concentration optimization in Ge(1+x)-ySbyTe
No full textOwing to superior thermoelectric properties, GeTe shows practical applications in power generation and refrigeration. However, the high carrier concentration limits its high performance. Here, a stepwise design, called Ge-vacancy suppression and Sb-doping of Ge(1+x)−ySbyTe, has been developed to optimize the carrier concentration. Considering that the extra Ge restricts the formation of Ge vacancies to reduce the carrier concentration and over-excessive Ge induces an increased lattice thermal conductivity, we use the foundation composition of Ge1.04Te for optimization. Based on the small electronegativity difference between Sb and Ge and the correspondingly high substitution limit, Sb doping is designed to tune the carrier concentration closer to the optimal level with the highest power factor. In the end, an enhanced figure of merit of 1.7 at 723 K can be achieved in Ge0.96Sb0.08Te. This study indicates that the stepwise design can optimize the carrier concentration of GeTe-based thermoelectric materials more effectively contributing to high figure of merit
Traces and shards of self-injury: Strange accounting with “Author X”
No full textIn this strange account autoethnography, three or four authors explore their lived experiences with self-injury. Strange accounting is both a post-modern style of text, and a method for keeping identities concealed when risks and secrets are in play. Author X, a post-modern place-keeper for an anonymous author who may or may not have contributed to this manuscript, introduces a new dimension and layer of concealment. With Author X in-play and under erasure, the reader will never be sure if there were three or four authors on this manuscript. Through strange accounting, a post-structuralist/postmodernist frame will be applied to understanding the self-injury experience. We frame self-injury as a social practice and, for some, an everyday norm, while remaining acutely aware of the stigma surrounding the topic of self-injury. Each of us, coupled with Author X, provide the others cover to trace stories of self-injury through the literature, our flesh, and our lives
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