Doping strategy for all carbon materials

The challange

1. Carbon is a very small atom. With an atomic number of 6, there are only 5 other atoms that are smaller than carbon. Compared to silicon with an atomic number of 14 the doping choices are minimal. Unlike silicon, elemental carbon can't be melt processed so existing tools & understanding about dopants (or more generally alloying) are out.

2. Carbon has a very rich chemistry. Elements like hydrogen & nitrogen that would become good candidates for doping actually form covalent bonds with carbon[1]. And instead of providing electron-hole pairs, the band gap continuously. Compare this with boron & phosphorus in silicon where they act more or less in their free atomic state. Sure with careful engineering maybe hydrogen & nitrogen can be made to fit inside carbon lattice (nitrogen happily sits inside diamond for example & it would be expected that it would act as a dopant in diamond like carbon as well)

3. The crystal arrangements of carbon that allow dopants to persist suffers from major problems.Pure diamond is hard to fabricate [2] diamond like carbon is much better in terms of energy required for fabrication but it needs to be deposited on a substrate(maybe free standing films can be created later) and also suffers from some of the same problems as other organic semiconductors (oxidation,high temperature instability etc)

Carbon has all the right properties and its probably the only element that can be used in any engineering discipline.The amount of attention that it gets is not unwarranted. But it has been incredibly frustrating that those properties have not been effectively utilised on a large scale.

Carbon fibers have only found application in aerospace parts due to their high price,organic semiconductors are unlikely to compete with silicon in transistors & solar cells. Carbon based materials are nowhere near competing with phosphors/base light sources in led. Overall carbon seems to be unable to move out of research & into the hands of consumers. Yearly award cermonies along with massive research grants have failed to produce desired results.Graphene & carbon nanotubes have now become a joke. Great only on paper.

The solution

We want to use all the amazing properties that graphitic carbon offers. Diamond is good for experiments & jewelery but for nothing else.

We need to be able to form films/macro sized materials. We need something like sio2 for silicon that acts as a dielectric. We need dopants that can change optoelectronic properties of carbon and allow it to be used as a material for fabricating transistors & leds.

The solution is simpler than it appears.

1. Carbon as a dopant for carbon materials.Size matches,free standing carbon exists & is stable (like in Polycyclic aromatic hydrocarbons which can act as dopant precursors, later carbonized to make carbon quantum dots providing free electrons & light emission as desired).

2. Glassy carbon doing the same thing sio2 does in silicon electronics.Providing an inert semi -insulating layer for what's inside[3].

3. Using macro scaled & nano scaled precursors with heteroatoms to make films of desired properties. Starting with nano materials will give more graphene like result & starting with macro materials will give more diamond like result(less conductivity,greater fraction of sp3 carbon).

https://akshatjiwannotes.blogspot.com/2024/10/all-carbon-organic-semiconductors.html

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1. By the way this applies also to transition metals like iron that are now a days becoming trendy as dopants especially in LED systems.

2.That amount of energy would be better spent in making sic that is a far better semiconductor,can operate at higher temperatures in an oxidative environment & has incredible engineering properties.Although its not as hard as diamond but its close enough to be used in cutting tools.

3. By increasing the concentration of sp3 bonded carbon it can be made less conducting & more transparent. Closer to diamond but with way less energy input. It still won't be perfectly clear(check out black diamonds) or fully insulating but thats fine. As long as it offers stark contrast to the graphene like properties inside the glassy layer.

Carbon is the king of elements.

Comments

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Notes by Akshat Jiwan Sharma

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