Which semiconductor material is noted for having an indirect band gap?

Silicon is notable for having an indirect band gap, which plays a significant role in its electronic and optoelectronic properties. In an indirect band gap semiconductor like silicon, the minimum energy point of the conduction band does not occur at the same momentum value (k-vector) as the maximum energy point of the valence band. This means that for an electron to transition from the valence band to the conduction band, it requires not only energy in terms of photons but also a change in momentum, typically facilitated by interactions with lattice vibrations (phonons).

This momentum requirement is a key reason why silicon is less efficient in light emission compared to direct band gap semiconductors, where electronic transitions can occur more easily without the need for additional momentum. Silicon, having a band gap of about 1.1 eV at room temperature, is widely used in electronic components and photovoltaic cells, although its indirect band gap leads to non-ideal characteristics for applications requiring efficient light emission, such as LEDs and laser diodes.

In contrast, materials like gallium arsenide and gallium phosphide have direct band gaps, allowing for more efficient light emission, while copper indium selenide also features a direct band gap useful in solar cell applications. Understanding