## What is the difference between electrical band gap and optical band gap?

Electrical band gap is the minimal energy required to create an electron hole pair in a semiconductor, whereas optical band gap is the exciton energy which determines the onset of vertical interband transitions.

## How is optical band gap measured?

The direct optical band gap of semiconductors is traditionally measured by extrapolating the linear region of the square of the absorption curve to the x-axis, and a variation of this method, developed by Tauc, has also been widely used.

**What is direct band?**

The band gap is called “direct” if the crystal momentum of electrons and holes is the same in both the conduction band and the valence band; an electron can directly emit a photon.

### What is direct & indirect band gap?

If the k-vectors are different, the material has an “indirect gap”. The band gap is called “direct” if the crystal momentum of electrons and holes is the same in both the conduction band and the valence band; an electron can directly emit a photon.

### What is K in Ek diagram?

the momentum wave number (k) which means k is the measure of the momentum of the particle.

**What is the difference between optical band gap and electrical band gap?**

Electrical band gap is simply the difference between the top of the valence band, and the bottom of the conduction band. For the optical band gap, you need to know where the higher energetic electrons are in the valence band, and determine the energy they need to reach the lowest energy level AVAILABLE on the conduction band.

#### What is the electrical band gap of a photon?

The Electrical Band Gap is the Optical Band Gap plus the Energy Gap requiered to separate the Electron-Hole pair (exciton) and end with an unbonded Electron and Hole pair again. i.e. Optical Band Gap = cut off frecuency(energy) of the absorbed photon Electrical Band Gap = Optical Band Gap + Exciton Binding energy

#### Is the Tauc band gap still useful for optical gap measurement?

A more physically based quantum well model was developed [ 128] to take account of these problems. However, the Tauc band gap, because of the ease with which it can be measured, is still widely used as an indication of the optical gap and a means of comparison between different films.

**What is the fundamental gap in optical absorption?**

This gap is also called fundamental gap, and is dipole forbidden [16,17]. In ellipsometric studies, absorption onsets at 4.28 and 5.42 eV corresponding to electric field polarization perpendicular and parallel to the optical axis are reported [16]. A quasiparticle gap of 3.65 eV has been calculated [17].