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The O2+ probe-sample conditions and subsequent data analysis required to obtain high depth resolution SIMS depth profiles from Si1− xGe x/Ge quantum well structures (0.6 ≤ x ≤ 1) are presented. For primary beam energies Ep >500 eV and x approaching 1, a significant decrease in the Ge+ ionisation probability resulted in unrepresentative and unquantifiable depth profiles. For Ep ≤ 500 eV, a monotonic increase in the Ge+ signal with x was observed resulting in profiles representative of the sample structure and enabling x to be found. A depth scale was also established using a point-by-point approach taking into account the local erosion rate, which is a function of x. Both the composition and the thickness of the Si1− xGe x and Ge layers were found to be in excellent agreement with those obtained using X-ray and transmission electron microscopy. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The thermal stability of thin (110 nm) compressively strained Ge surface channels, grown by reduced-pressure chemical vapor deposition on high quality relaxed Si0.2Ge0.8 reverse-graded buffers, has been investigated using in-situ hydrogen annealing at temperatures up to 650°C. Strain relaxation was observed and found to increase for thicker channels and higher anneal temperatures. For a Ge channel thickness ⩽45 nm, an increased surface roughening was found to dominate the strain relaxation process, which culminated in islanding. For the thicker (⩾45 nm) Ge channels misfit dislocation generation appeared to be the most dominant mechanism. Our results show that low thermal budgets (T < 550°C) should be employed for the fabrication of ~0.65% lattice mismatch strained Ge channels currently being developed for applications in CMOS-based devices and strained Ge-on-insulator platforms. [ABSTRACT FROM AUTHOR]

Abstract: Growth procedure and excellent properties of very thin 240nm thick, 95% relaxed, high Ge content Si0.3Ge0.7 buffer grown on SOI(001) substrate are demonstrated. All epilayers of the newly developed Si0.3Ge0.7/SOI(001) variable-temperature virtual substrate were grown in a single process by solid-source molecular beam epitaxy. Surface analysis of grown samples revealed smooth, cross-hatch free surface with low root mean square surface roughness of 0.9nm and low threading dislocations density of 5×104 cm−2. [Copyright &y& Elsevier]

The weak localization and interaction effects for charge carriers in a two-dimensional hole gas in a pure germanium quantum well in a SiGe/Ge/SiGe heterostructure with a hole density of 5.68×1011 cm-2 and mobility of 4.68×104 cm2 V-1 s-1 are investigated. The resistance measurements were made at temperatures from 46 mK to 10 K and magnetic fields up to 15 T. The magnetic-field dependence of the resistivity exhibits Shubnikov-de Haas oscillations and quantum Hall effect steps. At very low magnetic fields (B<0.1 T) a weak localization effect for holes is revealed, which makes for a negative magnetoresistance and growth of the resistance with decreasing temperature (at T<2 K). The manifestation of the interaction effect is observed and analyzed over a wide range of temperatures and magnetic fields. With increasing temperature the manifestation of the interaction-induced quantum correction passes from the diffusive regime to an intermediate and then to the ballistic regime. In all regions the behavior of the interaction quantum correction is in good agreement with the modern theoretical predictions. [ABSTRACT FROM AUTHOR]

The Shubnikov–de Haas oscillations in a two-dimensional hole gas in a quantum well of pure germanium in a SiGe/Ge/SiGe heterostructure with a hole concentration pH=5.68×1011 cm2 and mobility μ=4.68×104 cm2V-1s-1 are investigated in magnetic fields up to 15 T at temperatures from 40 mK to 4 K. The observed deviation from the known relation describing the conductivity oscillations in the Shubnikov–de Haas effect are explained by additional broadening of the Landau levels due to the existence of a nonuniform distribution of the concentration of charge carriers, and, accordingly, of their energy, in the plane of the two-dimensional gas. It is assumed that the latter is due to natural atomic-step variations of the well width. The effective hole mass (m*=0.112m0) is determined from the temperature dependence of the oscillation amplitude, and its dependence on magnetic field is used to determine the quantum scattering time and the value of the carrier concentration fluctuations. [ABSTRACT FROM AUTHOR]

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 293 K. Three times lower LF noise over 1–100 Hz range at VDS=−50 mV and VG−VTH=−1.5 V was measured for the 0.55 μm effective gate length p-Si0.3Ge0.7 MOSFET compared with p-Si MOSFET. Over three times drain current enhancement in saturation region of output current–voltage characteristics at VDS=−2.5 V for a 0.55 μm p-Si0.3Ge0.7 MOSFET in comparison with p-Si MOSFET is observed. [Copyright &y& Elsevier]

The magnetic-field dependence (up to 110 kOe) of the resistance of Si[sub0.7]Ge[sub0.3] /Si[sub0.2]Ge[sub0.8]/Si[sub0.7]Ge[sub0.3] with a 2D hole gas in a Si[sub0.2]Ge[sub0.8] quantum well is measured in the temperature range 0.335-10 K and in a range of variation of the currents from 100 nA to 50 μA. Shubnikov-de Haas oscillations are observed in the region of high magnetic fields, and in the low-field region H &les; 1 kOe a positive magnetoresistance is observed which gives way to a negative magnetoresistance as the field is increased. This peculiarity is explained by effects of weak localization of the 2D charge carriers under conditions when the spin-orbit scattering time τ[SUBso] is close to the inelastic scattering time τ[SUBϕ], and it is evidence of a splitting of the spin states under the influence of a perturbing potential due to the formation of a two-dimensional potential well (the Rashba mechanism). Analysis of the weak localization effects gave the values of the characteristic relaxation times as τ[SUBϕ] = 7.2T[SUP-1] × 10[SUP-12] s and τ[SUBso] = 1.36 × 10[SUP-12] s. From these characteristics of the heterostructure studied, a value of Δ = 2.97 meV was obtained for the spin splitting. [ABSTRACT FROM AUTHOR]

The growth of Si1-xGex quantum wells with high Ge composition (x>0.5) on Si(001) substrates by MBE is of great interest both for HMOS device applications and fundamental research. One of the possibilities to obtain a high Ge content Si1-xGex channel for mobile carriers, while retaining its strain, is to grow a relaxed Si1-yGey buffer layer on an underlying Si substrate. Such a buffer is termed a virtual substrate (VS), which is a constituent of SiGe metamorphic heterostructures. The effect of annealing on the structure of the Si(001)/VS/Si0.7Ge0.3/Si0.2Ge0.8/Si0.7Ge0.3 heterostructures was studied by grazing angle of incidence RBS. The thickness of the Si0.2Ge0.8 channel is inhomogeneous, which makes the analysis of the data by traditional means very hard. We have developed a model whereby the influence of the thickness inhomogeneity of each layer in the apparent energy resolution as a function of depth can be calculated. Automatic fits to the data were performed, and the roughness parameters, that is, the standard deviation of the thickness inhomogeneity of the relevant layers, were obtained, together with the thickness and stoichiometry of each layer. The results are compared with TEM and high resolution XRD experiments. [ABSTRACT FROM AUTHOR]

Epitaxial growth of a compressively strained Ge quantum well (QW) on an ultrathin, 345 nm thick, Si0.4Ge0.6/LT-Si0.4Ge0.6/Si(001) virtual substrate (VS) has been demonstrated. The VS, grown with a low temperature Si0.4Ge0.6 seed layer on a Si(001) substrate, is found to be fully relaxed and the Ge QW is fully strained. The temperature dependence of Hall mobility and carrier density clearly indicates a two-dimensional hole gas in the Ge QW. At room temperature, which is more relevant for electronic devices applications, the samples show a very high Hall mobility of 1235 cm2 V-1 s-1 at a carrier density of 2.36×1012 cm-2. [ABSTRACT FROM AUTHOR]

We report an ultrahigh room-temperature hole drift mobility obtained in a Si0.2Ge0.8 quantum well with a parabolic-like Ge profile, which has at its core a p-type modulation-doped (MOD) Si/Si0.2Ge0.8/Si0.65Ge0.35/Si(001) heterostructure. High-conductivity holes at 293 K with a drift mobility of 3600 cm2 V-1 s-1 at a sheet carrier density of 4.94×1012 cm-2 were obtained in the Si0.2Ge0.8 quantum well after optimum annealing at 750 °C for 30 min. Hall mobility and sheet carrier density of this heterostructure are 1776 cm2 V-1 s-1 and 2.37×1013 cm-2, respectively. Structural characterization of the as-grown and the annealed samples revealed that the annealing had caused Si0.2Ge0.8 channel broadening, smearing of interfaces, and formation of a parabolic-like Ge profile that significantly improved room-temperature hole transport properties. The reported values of hole mobility are much higher than in the bulk Ge. [ABSTRACT FROM AUTHOR]

We have demonstrated reduced 1/f low-frequency noise in sub-μm metamorphic high Ge content p-Si[sub 0.3]Ge[sub 0.7] metal–oxide–semiconductor field-effect transistors (MOSFETs) at 293 K. Three times lower normalized power spectral density (NPSD) S[sub I[sub D]]/I[sub D][sup 2] of drain current fluctuations over the 1–100 Hz range at V[sub DS]=-50 mV and V[sub G]-V[sub th]=-1.5 V was measured for a 0.55 μm effective gate length p-Si[sub 0.3]Ge[sub 0.7] MOSFET compared with a p-Si MOSFET. Performed quantitative analysis clearly demonstrates the importance of carrier number fluctuations and correlated mobility fluctuations (CMFs) components of 1/f noise for p-Si surface channel MOSFETs, and the absence of CMFs for p-Si[sub 0.3]Ge[sub 0.7] buried channel MOSFETs. This explains the reduced NPSD for p-Si[sub 0.3]Ge[sub 0.7] MOSFETs in strong inversion. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of post-growth furnace thermal annealing (FTA) on the Hall mobility and sheet carrier density measured at 9–300 K in the Si[sub 0.2]Ge[sub 0.8]/Si[sub 0.7]Ge[sub 0.3]/Si(001) p-type modulation-doped heterostructures was studied. FTA treatments in the temperature range of 600–900 °C for 30 min were performed on similar heterostructures but with two Si[sub 0.2]Ge[sub 0.8] channel thicknesses. The annealing at 600 °C is seen to have a negligible effect on the Hall mobility as well as on the sheet carrier density. Increases in the annealing temperature resulted in pronounced successive increases of the mobility. For both samples the maximum Hall mobility was observed after FTA at 750 °C. Further increases of the annealing temperature resulted in a decrease in mobility. The sheet carrier density showed the opposite behavior with an increase in annealing temperature. The mechanism causing this behavior is discussed. Structural characterization of as-grown and annealed samples was done by cross-sectional transmission electron microscopy. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

To extract the room-temperature drift mobility and sheet carrier density of two-dimensional hole gas (2DHG) that form in Ge strained channels of various thicknesses in Ge/Si[sub 0.33]Ge[sub 0.67]/Si(001) p-type modulation-doped heterostructures, the magnetic field dependences of the magnetoresistance and Hall resistance at temperature of 295 K were measured and the technique of maximum entropy mobility spectrum analysis was applied. This technique allows a unique determination of mobility and sheet carrier density of each group of carriers present in parallel conducting multilayers semiconductor heterostructures. Extremely high room-temperature drift mobility (at sheet carrier density) of 2DHG 2940 cm[sup 2] V[sup -1] s[sup -1] (5.11×10[sup 11] cm[sup -2]) was obtained in a sample with a 20 nm thick Ge strained channel. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Epitaxial growth of Ge on Si has been investigated in order to produce high quality Ge layers on (110)- and (111)-orientated Si substrates, which are of considerable interest for their predicted superior electronic properties compared to (100) orientation. Using the low temperature/high temperature growth technique in reduced pressure chemical vapour deposition, high quality (111) Ge layers have been demonstrated almost entirely suppressing the formation of stacking faults (< 107 cm-2) with a very low rms roughness of less than 2 nm and a reduction in threading dislocation density (TDD) (∼ 3 × 108 cm-2). The leading factor in improving the buffer quality was use of a thin, partially relaxed Ge seed layer, where the residual compressive strain promotes an intermediate islanding step between the low temperature and high temperature growth phases. (110)-oriented layers were also examined and found to have similar low rms roughness (1.6 nm) and TDD below 108 cm-2, although use of a thin seed layer did not offer the same relative improvement seen for (111). [ABSTRACT FROM AUTHOR]