What Is a Direct Semiconductor?

Examples of direct band gap semiconductors: GaAs, InP semiconductors. In contrast, Si and Ge are indirect band gap semiconductors.
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Direct bandgap semiconductor materials are semiconductors where the minimum value of the conduction band (bottom of the conduction band) and the maximum value of the valence band (top of the valence band) are in the same position in k-space. To transfer electrons to the conduction band to generate conductive electrons and holes (forming a half-full energy band), it only needs to absorb energy.

Important properties of direct bandgap semiconductors: When the valence band electron transitions to the conduction band, the electron wave vector does not change, and the energy band diagram is a vertical transition. This means that the momentum of the electron can be maintained during the transition process. Change-meet the law of conservation of momentum. Conversely, if the conduction band electron drops to the valence band (that is, the electron and hole recombine), the momentum can also be maintained-direct recombination, that is, the recombination of electrons and holes will occur as soon as they meet (no phonon is required to accept Or provide momentum). Therefore, the lifetime of carriers in direct bandgap semiconductors is often short; at the same time, this direct recombination can release almost all energy in the form of light (photon momentum is close to zero, no phonon participation is required)-high luminous efficiency (This is also the fundamental reason why most light-emitting devices are made with direct bandgap semiconductors).