In solid-state physics, a band gap/energy gap is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in eV) between the top of the VB and the bottom of the CB in insulators and semiconductors. It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move within the crystal lattice and serve as a charge carrier to conduct electric current.

A semiconductor will not absorb photons of energy less than the band gap and the energy of the electron-hole pair produced by a photon is equal to the band gap energy.

The band gap is a major factor determining the electrical conductivity of a solid. Band-gap engineering is the process of controlling/tuning the band gap of a material by controlling the composition of certain semiconductor alloys, such as GaAlAs, InGaAs, and InAlAs. Band gap depends on doping, size, temperature, pressure etc. It is also possible to construct layered materials with alternating compositions by techniques like molecular-beam epitaxy. These methods are exploited in the design of heterojunction bipolar transistors (HBTs), laser diodes and solar cells.

In a quantum dot crystal, the band gap is size dependent and can be altered to produce a range of energies between the valence band and conduction band. Band gap increases with decrease in size due to electron confinement at Nano-scale. It is also known as Quantum confinement effect.

However, I am working on inorganic semiconducting silicide materials for potential applications in solar cells. Beta phase Iron di-silicide (β-FeSi2) has a band gap of about 0.87 eV which can be tuned from 0.8 eV to less than 0.9 eV.

How can we increase its band gap further, beyond 0.9 eV? In particular, can we tune its band gap near to optimum band gap of 1.5 eV for solar energy harvesting?

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