What is phonon band gap?

Jin-Wu Jiang. The phonon band structure of monolayer MoS2 is characteristic for a large energy gap between acoustic and optical branches, which protects the vibration of acoustic modes from being scattered by optical phonon modes.

What is an indirect band gap material?

In an “indirect” gap, a photon cannot be emitted because the electron must pass through an intermediate state and transfer momentum to the crystal lattice. Examples of direct bandgap materials include amorphous silicon and some III-V materials such as InAs and GaAs.

What is a phonon mode?

A phonon is the quantum mechanical description of an elementary vibrational motion in which a lattice of atoms or molecules uniformly oscillates at a single frequency. In classical mechanics this designates a normal mode of vibration.

What is a band gap material?

A band gap is a range of energy levels in a material in which electrons cannot exist. The absence or presence of a band gap as well as its size can help us understand the electronic behaviour of a material a. nd distinguish electrical insulators, conductors, and semiconductors [1].

How is the band gap of a material determined?

If the momentum of the lowest energy state in the conduction band and the highest energy state of the valence band of a material are the same, the material has a direct bandgap. If they are not the same, then the material has an indirect band gap.

Which of the following is known as indirect band gap semiconductor?

Which of the following is known as indirect band gap semiconductors? Explanation: The elemental semiconductor is made up of a single element from the fourth column elements such as Germanium. Here recombination takes place takes place via traps. It is called indirect band gap semiconductors.

What causes phonons in lattice vibration?

Optical Phonons Optical phonon are quantized modes of lattice vibrations when two or more charged particles in a primitive cell move in opposite directions with the center of mass at rest. This mode has highest energy for wavelength infinity or k=0 when the two lattices move in opposing direction of each other.

How do you find the direct and indirect band gap?

The minimum energy gap is the difference in energy between the conduction band-edge and the valence band edge. If both the band edges are at the same k-point of the Brillouin zone, the band gap is direct. If these differ by a finite wave vector, the band gap is indirect.

Which of the following is example of indirect band gap?

Examples for indirect band gap semiconductor materials are silicon (Si), germanium (Ge), aluminum arsenide (AlAs) and gallium phosphide (GaP).