24,370 research outputs found
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
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
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
Ge-on-Si single-photon avalanche diode detectors: design, modeling, fabrication, and characterization at wavelengths 1310 and 1550 nm
No full textThe design, modeling, fabrication, and characterization of single-photon avalanche diode detectors with an epitaxial Ge absorption region grown directly on Si are presented. At 100 K, a single-photon detection efficiency of 4% at 1310 nm wavelength was measured with a dark count rate of ~ 6 megacounts/s, resulting in the lowest reported noise-equivalent power for a Ge-on-Si single-photon avalanche diode detector (1×10-14 WHz-1/2). The first report of 1550 nm wavelength detection efficiency measurements with such a device is presented. A jitter of 300 ps was measured, and preliminary tests on after-pulsing showed only a small increase (a factor of 2) in the normalized dark count rate when the gating frequency was increased from 1 kHz to 1 MHz. These initial results suggest that optimized devices integrated on Si substrates could potentially provide performance comparable to or better than that of many commercially available discrete technologies
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
Synthesis and structural characterization of monomeric heterobimetallic oxides with a Ge(II)-O-M skeleton (M = Yb, Y)
No full textThe germanium hydroxide complexes LGe(mu-O)M(THF)Cp(2) (M = Yb, 1; Y, 2; L = HC[C(Me)N(Ar)](2); Ar = 2,6-iPr(2)C(6)H(3)) were prepared by the reaction of LGeOH with Cp(3)M (M = Yb, Y) in THF at ambient temperature with the elimination of HCp. 1 and 2 are pale-yellow solids. Both compounds crystallize isotypically as monomers in a triclinic space group P (1) over bar (pseudo- merohedrally twinned, two independent molecules) and were found to be stable in the solid state and in solution at room temperature. The six-membered C(3)N(2)Ge rings in 1 and 2 display a boat conformation with the germanium and the gamma-C out-of-plane. The Ge-O-M skeleton exhibits a bent arrangement (angles 151-154 degrees). The (1)H NMR investigation of 2 confirmed that the solid-state structure is also found in solution
Practicability and fundamental performance of alkali treated raw bamboo fiber reinforced high performance seawater sea sand concrete
No full textStability and composition of Ni-germanosilicided Si/sub 1-x/Ge/sub x/ films
No full textThe stability and composition of the Ni-germanosilicided films formed on relaxed Si/sub 1-x/Ge/sub x/ alloy has been studied in the temperature range of 400-900 degrees C. During the solid phase thermal reaction between Ni and Si/sub 1-x/Ge/sub x/, a nickel-germanosilicide Ni/sub y/(Si/sub 1-w/Ge/sub w/)/sub 1-y/ ternary phase (w[left angle bracket]or=x and y approximately=0.5) and a Ge-rich Si/sub 1-z/Ge/sub z/ phase (z[right angle bracket]x) have been found. In the lower annealing temperature range of 500 degrees C, the Ge composition in the nickel-germanosilicide phase is similar to that of the Si/sub 0.75/Ge/sub 0.25/ substrate. At the same time, germination of Si/sub 1-z/Ge/sub z/ (z[right angle bracket]x) takes place within the germanosilicide film. At higher annealing temperatures, Ni thermodynamically prefers to react with Si compared to Ge, and as a result, Ge segregates out from the germanosilicide grains to enrich Ge in the formed Si/sub 1-z/Ge/sub z/ (z[right angle bracket]x) grains in between the germanosilicide grains. On the other hand, the size of the germanosilicide grains increases almost linearly with annealing temperature while that for the Si/sub 1-z/Ge/sub z/ grains remains almost constant up to an annealing temperature of 700 degrees C, and above which it increases sharply. As a result, the Ge-rich Si/sub 1-z/Ge/sub z/ grains make the germanosilicide film discontinuous, leading to an increase in the sheet resistance of the germanosilicide film. (31 References)
Optical absorption in highly strained Ge/SiGe quantum wells: The role of Γ→Δ scattering
No full textWe report the observation of the quantum-confined Stark effect in Ge/SiGe multiple quantum well heterostructures grown on Si0.22Ge0.78 virtual substrates. The large compressive strain in the Ge quantum well layers caused by the lattice mismatch with the virtual substrate results in a blue shift of the direct absorption edge, as well as a reduction in the Γ-valley scattering lifetime because of strain-induced splittings of the conduction band valleys. We investigate theoretically the Γ-valley carrier lifetimes by evaluating the Γ→L and Γ→Δ scattering rates in strained Ge/SiGe semiconductor heterostructures. These scattering rates are used to determine the lifetime broadening of excitonic peaks and the indirect absorption in simulated absorption spectra, which are compared with measured absorption spectra for quantum well structures with systematically varied dimensions. We find that Γ→Δ scattering is significant in compressively strained Ge quantum wells and that the Γ-valley electron lifetime is less than 50 fs in the highly strained structures reported here, where Γ→Δ scattering accounted for approximately half of the total scattering rate
- …
