Certain group III – V compounds such as gallium arsenide (GaAs) and indium antimonide (InSb) have far smaller effective masses than tetrahedral group IV materials like silicon and germanium. In the simplest Drude picture of electronic transport, the maximum obtainable charge carrier velocity is inversely proportional to the effective mass: v → → = ‖ μ μ ‖ ⋅ ⋅ E → → , where ‖ μ μ ‖ = e τ τ / ‖ m ∗ ∗ ‖ with e being the electronic charge. The ultimate speed of integrated circuits depends on the carrier velocity, so the low effective mass is the fundamental reason that GaAs and its derivatives are used instead of Si in high- bandwidth applications like cellular telephony.