Structural and Compositional Properties of Strain-Symmetrized SiGe/Si Heterostructures

Ross, I. M.; Gass, M; Walther, T.; Bleloch, Andrew; Cullis, A. G.; Lever, L.; Ikonić, Z.; Califano, Marco; Kelsall, R. W.; Zhang, J; Paul, Douglas J.

doi:10.1007/978-1-4020-8615-1_59

Cited by 3 publications

(2 citation statements)

References 6 publications

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“…This system has a far lower effective mass of about which is crucial to not only improving the gain through higher wavefunction overlap and matrix elements, but also as lower effective masses improve the tolerance of subband alignment to growth inaccuracies [108]. Indeed Valavanis et al [108] have used the diffusion profiles measured by TEM [122] to provide more accurate modelling of the subband positions due to rounding of the heterostructure barrier profiles from Ge segregation and diffusion. A number of designs have been suggested with Ge quantum wells with gain well above the waveguide losses not only at 4 K but also at room temperature.…”

Section: Discussionmentioning

confidence: 99%

The progress towards terahertz quantum cascade lasers on silicon substrates

Paul¹

2010

Laser & Photonics Reviews

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A review is presented of work over the last 10 years which has been aimed at trying to produce a Si-based THz quantum cascade laser. Potential THz applications and present THz sources will be briefly discussed before the materials issues with the Si/SiGe system is discussed. Waveguide designs and waveguide losses will be presented. Experimental measurements of the non-radiative lifetimes for intersubband transitions in Si Ge quantum wells will be presented along with theory explaining the important scattering mechanisms which determine the lifetimes. Examples of p-type Si/SiGe quantum cascade designs with the experimental electroluminescence will be reviewed and examples of n-type Si-based designs will be presented. In the conclusion designs and structures will be discussed with the greatest potential to achieve an electrically pumped Si-based THz laser.

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Section: Discussionmentioning

confidence: 99%

The progress towards terahertz quantum cascade lasers on silicon substrates

Paul¹

2010

Laser & Photonics Reviews

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“…For sample 1 grown at the L-NESS in Como, a small segregation length of 0.1 nm has been estimated by comparing dynamical simulations to results from x-ray diffraction ͑XRD͒ measurements 29 while for sample 2 grown at Imperial College, a segregation length of 1.0 nm was used which was obtained from highresolution transmission electron microscopy ͑TEM͒ measurements. 30 Two different growth systems have been used for the two samples grown for this work ͑Fig. 1͒.…”

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confidence: 99%

Si/SiGe quantum cascade superlattice designs for terahertz emission

Matmon

Paul

Lever

et al. 2010

Journal of Applied Physics

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Quantum cascade lasers ͑QCLs͒ are compact sources that have demonstrated high output powers at terahertz ͑THz͒ frequencies. To date, all THz QCLs have been realized in III-V materials. Results are presented from Si 1−x Ge x quantum cascade superlattice designs emitting at around 3 THz which have been grown in two different chemical vapor deposition systems. The key to achieving successful electroluminescence at THz frequencies in a p-type system has been to strain the light-hole states to energies well above the radiative subband states. To accurately model the emission wavelengths, a 6-band k · p tool which includes the effects of nonabrupt heterointerfaces has been used to predict the characteristics of the emitters. X-ray diffraction and transmission electron microscopy have been used along with Fourier transform infrared spectroscopy to fully characterize the samples. A number of methods to improve the gain from the designs are suggested.

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Interfacial sharpness and intermixing in a Ge-SiGe multiple quantum well structure

Bashir

Gallacher

Millar

et al. 2018

Journal of Applied Physics

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A Ge-SiGe multiple quantum well structure created by low energy plasma enhanced chemical vapour deposition, with nominal well thickness of 5.4 nm separated by 3.6 nm SiGe spacers, is analysed quantitatively using scanning transmission electron microscopy. Both high angle annular dark field imaging and electron energy loss spectroscopy show that the interfaces are not completely sharp, suggesting that there is some intermixing of Si and Ge at each interface. Two methods are compared for the quantification of the spectroscopy datasets: a self-consistent approach that calculates binary substitutional trends without requiring experimental or computational k-factors from elsewhere and a standards-based cross sectional calculation. Whilst the cross section approach is shown to be ultimately more reliable, the self-consistent approach provides surprisingly good results. It is found that the Ge quantum wells are actually about 95% Ge and that the spacers, whilst apparently peaking at about 35% Si, contain significant interdiffused Ge at each side. This result is shown to be not just an artefact of electron beam spreading in the sample, but mostly arising from a real chemical interdiffusion resulting from the growth. Similar results are found by use of X-ray diffraction from a similar area of the sample. Putting the results together suggests a real interdiffusion with a standard deviation of about 0.87 nm, or put another way—a true width defined from 10%–90% of the compositional gradient of about 2.9 nm. This suggests an intrinsic limit on how sharp such interfaces can be grown by this method and, whilst 95% Ge quantum wells (QWs) still behave well enough to have good properties, any attempt to grow thinner QWs would require modifications to the growth procedure to reduce this interdiffusion, in order to maintain a composition of ≥95% Ge.

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Structural and Compositional Properties of Strain-Symmetrized SiGe/Si Heterostructures

Cited by 3 publications

References 6 publications

The progress towards terahertz quantum cascade lasers on silicon substrates

The progress towards terahertz quantum cascade lasers on silicon substrates

Si/SiGe quantum cascade superlattice designs for terahertz emission

Interfacial sharpness and intermixing in a Ge-SiGe multiple quantum well structure

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