What are direct and indirect semiconductor materials?
In semiconductor physics, the band gap of a semiconductor can be of two basic types, a direct band gap or an indirect band gap. Examples of direct bandgap materials include amorphous silicon and some III-V materials such as InAs and GaAs. Indirect bandgap materials include crystalline silicon and Ge.
What is the difference between direct and indirect transition?
In a direct band gap semiconductor, the top of the valence band and the bottom of the conduction band occur at the same value of momentum. In an indirect band gap semiconductor, the maximum energy of the valence band occurs at a different value of momentum to the minimum in the conduction band energy.
What are indirect semiconductors?
Examples of “indirect” semiconductors are Si, Ge, and GaP. In this case, the transition between the maximum of valence band to the minimum of the conductive band is not possible with only the absorption of photon with energy hν close to the bandgap Wg.
What are the applications of direct and indirect band gap semiconductors?
As a result of such considerations, gallium arsenide and other direct band gap semiconductors are used to make optical devices such as LEDs and semiconductor lasers, whereas silicon, which is an indirect band gap semiconductor, is not.
Which copper is a direct band gap material?
Cu(In1-x Gax)Se2 is one of the most promising absorber material for PV applications. It is a direct band gap semiconductor. Its energy band gap ( E g) is within the range of 1.06–1.7 eV. The exact value of E g depends on Ga/(Ga+In) ratio.
Is germanium direct band gap?
As a promising material for fabricating on-chip optoelectronic devices, germanium (Ge) has a direct band gap of 0.8 eV, which matches with the wavelength for optical communication. The energy difference is only 134 meV between direct and indirect band gaps, implying the possibility of a direct band gap light emission.
What is valence band in semiconductor?
The valence band is the band of electron orbitals that electrons can jump out of, moving into the conduction band when excited. The valence band is simply the outermost electron orbital of an atom of any specific material that electrons actually occupy.
Is Silicon a direct band gap semiconductor?
It is well known that Si is an indirect band gap semiconductor with a large energy difference between the direct gap (3.5 eV) and the indirect gap (1.1 eV).
Is Silicon direct or indirect band gap?
What are direct semiconductors?
A direct semiconductor is used when the valence and conduction bands have the same momentum. This semiconductor is important in radiative recombination, in which an electron jumps from one band to the other. In the science of energy, a direct semiconductor works with two bands.
Is CIGS direct band gap?
2.2. It is a direct band gap semiconductor. Its energy band gap ( E g) is within the range of 1.06–1.7 eV.
What is the bandgap of SI?
1.12 eV
Si (Silicon) has a band gap of 1.12 eV (electron volt). A semiconductor with a large value is called a wide-band-gap semiconductor.
Direct or indirect transition are ”allowed” transitions, if the momentum matrix element charaterizing the transition is different from zero. This means that the transition can hold for sure if sufficient energy is given to the particle (e.g. electron) involved in the process.
What is the difference between a direct and an indirect semiconductor?
In direct semiconductors, a direct interaction of electrons, holes and photons is possible without any additional particle. Indirect semiconductors, however, require an additional phonon for conservation of energy and crystal momentum.
What are the transitions in an indirect bandgap?
For an indirect bandgap, the transitions are oblique. An indirect bandgap is formed between the energy minimum of a highest band (e.g. conduction band) which occurs at a value of the wavevector ko which is different from that k1 at which occurs the energy maximum of a lower band (e.g. valence band).
What are the two types of semiconductors?
By definition, there are two classes of semiconductors, direct and indirect. For interactions between electrons, holes and photons, conservation of energy and crystal momentum has to apply. In direct semiconductors, a direct interaction of electrons, holes and photons is possible without any additional particle.