Direct bandgap

In semiconductor physics, a direct bandgap means that the conduction band lies directly above the valence band, in momentum space (see E-k plots[?]). A semiconductor with a direct bandgap can be used to emit light. Indirect bandgap semiconductors such as crystalline silicon cannot.

The prime example of a direct bandgap semiconductor is gallium arsenide - a material commonly used in laser diodes.

See indirect bandgap for an explanation of the connection between bandgap offset and light emission.