Ge/Si Virtual Substrate for III-V multi-junction solar cells
Bibliographic record
Abstract
Multi-junction III-V concentrator cells have the most important energy conversion efficiency, competing with any other solar cell technology. Various cell designs have been proposed to achieve the efficiency of over 40% [1], [2]. Germanium appears to be the material of choice for the bottom cell to cover the IR part of solar spectrum. A high efficiency of 40.7% was measured for a metamorphic three-junction GaInP/GaInAs/Ge cell at 240 suns [3]. This architecture has achieved system efficiency of 30% [4]. A road map based on the integration of Ge on Si wafers can be a solution to replace the bulk Ge substrates for significant cost savings. However, due to the important 4.2% lattice mismatch between Si and Ge, strain is introduced in epitaxial Ge layers on Si which leads to the generation of a misfit dislocations network. Dislocations act as recombination centers for carriers and strongly influence the solar cell performance [5]. Several techniques of dislocation reduction were reported in the recent years [6]. However, the treading dislocations density (TDD) in the Ge layer remains higher than 106 cm-1. In this work, we propose a new architecture of low-cost virtual substrate engineering with acceptable TDD and surface roughness for III-V multi-junction solar cell. Ge/Si substrate was treated with post epitaxial process to create a denser nanovoids region in Ge layer according to the mass transport mechanism [7]. Fig 1. shows cross section SEM view of self-assembled nanovoids in Ge layer/Si obtained after electrochemical porosification and thermal annealing [8]-[17]. The idea here is to use voids as a barrier for threading dislocations propagation. In this presentation, we will present detailed optimization of the porosification and the annealing of Ge on Si and study the effect of different process parameters on TDD and on surface roughness. The resulting surface can be used as the starting point for the deposition of the III–V junctions in the 3J PV cell. This engineered substrate concept is promising for the fabrication of dislocation-free Ge on Si substrate and would result in a significant cost reduction in multijunction solar cells cost.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".