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Nanocrystalline silicon

Nanocrystalline silicon is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nanocrystalline silicon rather than just read about it. In short: Nanocrystalline silicon (nc-Si), sometimes also known as microcrystalline silicon (μc-Si), is a form of porous silicon. It is an allotropic form of silicon with paracrystalline structure—is similar to amorphous silicon (a-Si), in that it has an amorphous phase.

Nanocrystalline silicon — main illustration
Nanocrystalline silicon — illustration

Key takeaways

  • Nanocrystalline silicon belongs to biology; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Nanocrystalline silicon to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Nanocrystalline silicon from memory before moving on to harder problems.

Reference excerpt

Nanocrystalline silicon (nc-Si), sometimes also known as microcrystalline silicon (μc-Si), is a form of porous silicon. It is an allotropic form of silicon with paracrystalline structure—is similar to amorphous silicon (a-Si), in that it has an amorphous phase. Where they differ, however, is that nc-Si has small grains of crystalline silicon within the amorphous phase. This is in contrast to polycrystalline silicon (poly-Si) which consists solely of crystalline silicon grains, separated by grain boundaries. The difference comes solely from the grain size of the crystalline grains. Most materials with grains in the micrometre range are actually fine-grained polysilicon, so nanocrystalline silicon is a better term. The term Nanocrystalline silicon refers to a range of materials around the transition region from amorphous to microcrystalline phase in the silicon thin film. The crystalline volume fraction (as measured from Raman spectroscopy) is another criterion to describe the materials in this transition zone. nc-Si has many useful advantages over a-Si, one being that if grown properly it can have a higher electron mobility, due to the presence of the silicon crystallites. It also shows increased absorption in the red and infrared wavelengths, which make it an important material for use in a-Si solar cells. One of the most important advantages of nanocrystalline silicon, however, is that it has increased stability over a-Si, one of the reasons being because of its lower hydrogen concentration. Although it currently cannot attain the mobility that poly-Si can, it has the advantage over poly-Si that it is easier to fabricate, as it can be deposited using conventional low temperature a-Si deposition techniques, such as PECVD, as opposed to laser annealing or high temperature CVD processes, in the case of poly-Si.

Uses The main application of this novel material is in the field of silicon thin film solar cells. As nc-Si has about the same bandgap as crystalline silicon, which is ~1.12 eV, it can be combined in thin layers with a-Si, creating a layered, multi-junction cell called a tandem cell. The top cell in a-Si absorbs the visible light and leaves the infrared part of the spectrum for the bottom cell in nanocrystalline Si. A few companies are on the verge of commercializing silicon inks based on nanocrystalline silicon or on other silicon compounds. The semiconductor industry is also investigating the potential for nanocrystalline silicon, especially in the memory area.

Thin-film silicon Nanocrystalline silicon and small-grained polycrystalline silicon are considered thin-film silicon.

See also

References

External links Thin-film silicon solar cells.

Illustrations

Nanocrystalline silicon: Silicon nanopowder
Silicon nanopowder

Worked examples

Example 1 — a first encounter with Nanocrystalline silicon

Start with the simplest possible case. Write down what Nanocrystalline silicon claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nanocrystalline silicon before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nanocrystalline silicon ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nanocrystalline silicon

In research
Nanocrystalline silicon appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Nanocrystalline silicon in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Nanocrystalline silicon is common in secondary-school and first-year university syllabi. It links to neighbouring topics Allotropes of silicon, Group IV semiconductors, Nanomaterials, so understanding it makes those chapters shorter.
In everyday life
Look for Nanocrystalline silicon outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Nanocrystalline silicon in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Nanocrystalline silicon means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Nanocrystalline silicon out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nanocrystalline silicon in simple terms?

Nanocrystalline silicon (nc-Si), sometimes also known as microcrystalline silicon (μc-Si), is a form of porous silicon. It is an allotropic form of silicon with paracrystalline structure—is similar to amorphous silicon (a-Si), in that it has an amorphous phase.

Why does Nanocrystalline silicon matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nanocrystalline silicon?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nanocrystalline silicon.

Tags

  • Allotropes of silicon
  • Group IV semiconductors
  • Nanomaterials
  • Silicon solar cells
  • Thin-film cells

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