Electronic and Optical Properties of Short-Period Si/Sige Superlattices: Effects of Interfacial Atomic-Scale Roughness
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Bibliographic record
Abstract
SiGe/Si superlattice (SL) are currently a central building block of nanosheet transistors proposed for the 7 nm technology nodes and beyond [1], where elective wet-etching of the SiGe layers has been used to release the Si layers and form a vertically stacked channels architecture [2]. Consequently, the interfacial abruptness and uniformity in heterostructures are critical to control their electronic and optical properties. Recently, we demonstrated a 3-D atomistic-level mapping of the roughness and uniformity of buried epitaxial interfaces in Si/SiGe SLs with a layer thickness in the 1.5-7.5 nm range [3]. This direct quantification of the abruptness of buried interfaces enabled a direct evaluation of interfacial effects on electronic and optical properties of epitaxial heterostructures. For instance, spectroscopic ellipsometry indicated the first observation of a new superlattice-related optical transition between 2.2 and 2.7 eV. However, the interpretation of this new transition can only be achieved using a theoretical framework considering atomic-level details of the interfacial roughness. To that end, we have been carrying out theoretical investigations to build a correct quantum mechanical model that incorporates the effect of the interface, directly measured from atom probe tomography (APT), to interpret the possible SL-related optical transition. Thus, an 8-band k⋅p formalism was developed and validated for group IV semiconductors [4], where a quantum mechanical incorporation of the interface width is highly coveted because the microscopic interface asymmetry (MIA) effect can greatly influence the electronic and optical properties of short-period SLs, induce strong interactions between different SL subbands, and enhance the absorption strength considerably [5]. It has been shown that the nature of the SL interfaces can have a significative impact on the optical confinement properties of other group IV heterostructures [6]. To test this model, experimental optical characterization of four different SLs (the mean Ge concentration of the layers within the SLs is in the 25 to 30 at. % range and is the periodicity of the SLs) will be presented and discussed. Then, by simulating the SL optical properties with the developed 8-band k⋅p method, the effect of the interface will be investigated to try and explain the observed spectroscopic transition. [1] G. Hellings, et al , in 2018 IEEE Symp. VLSI Technol. (IEEE, 2018), pp. 85–86. [2] K. Komori, et al , Solid State Phenom. 282 , 107 (2018). [3] S. Mukherjee, et al , ArXiv: Cond-Mat 1908.00874 , 1 (2019). [4] T. B. Bahder, Phys. Rev. B 41 , 11992 (1990). [5] H. M. Dong, et al , Thin Solid Films 589 , 388 (2015). [6] F. Szmulowicz, et al , Phys. Rev. B - Condens. Matter Mater. Phys. 69 , 155321 (2004).
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it