For example, gallium arsenide (GaAs) has six times higher electron mobility than silicon, which allows faster operation; wider band gap, which allows operation of power devices at higher temperatures, and gives lower thermal noise to low power devices at room temperature; its direct band gap gives it more favorable optoelectronic properties than the indirect band gap of silicon; it can be alloyed to ternary and quaternary compositions, with adjustable band gap width, allowing light emission at chosen wavelengths, which makes possible matching to the wavelengths most efficiently transmitted through optical fibers.
[2] By alloying multiple compounds, some semiconductor materials are tunable, e.g., in band gap or lattice constant.
Lattice constants of the compounds also tend to be different, and the lattice mismatch against the substrate, dependent on the mixing ratio, causes defects in amounts dependent on the mismatch magnitude; this influences the ratio of achievable radiative/nonradiative recombinations and determines the luminous efficiency of the device.
[4] Metalorganic vapor-phase epitaxy (MOVPE) is the most popular deposition technology for the formation of compound semiconducting thin films for devices.
[citation needed] It uses ultrapure metalorganics and/or hydrides as precursor source materials in an ambient gas such as hydrogen.