directbandgap

Direct bandgap, in semiconductor physics, refers to a material whose conduction-band minimum and valence-band maximum occur at the same crystal momentum (k-value). In such materials, electrons can recombine with holes and emit a photon directly, without the need to change momentum via a phonon. This makes radiative transitions highly probable and efficient.

In contrast, indirect bandgap materials have their band extrema at different k-values. Recombination then requires phonon involvement to conserve momentum, which greatly reduces the probability of light emission. Indirect bandgap materials are typically less suitable for efficient light sources but can be advantageous for other roles, such as photovoltaics or certain transistors.

Direct bandgap semiconductors are essential for optoelectronic devices that emit light, including light-emitting diodes and laser diodes. Common direct-bandgap materials include gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), and cadmium telluride (CdTe). Silicon is indirect and thus not efficient as a light emitter, though it remains dominant in electronics and some photonic applications.

The bandgap energy determines the color of emitted or absorbed photons and can be tuned by composition, alloying, strain, and quantum confinement in nanostructures. Direct bandgaps enable high-efficiency light emission and are a central focus in the development of LEDs, laser sources, and display technologies, as well as in certain high-speed optical communications materials.