modfets can be manufactured by epitaxial growth of a strained sige layer. in the strained layer, the germanium content increases linearly to around 40-50%. this concentration of germanium allows the formation of a quantum well structure with a high conduction band offset and a high density of very mobile charge carriers. the end result is a fet with ultra-high switching speeds and low noise. ingaas/algaas, algan/ingan, and other compounds are also used in place of sige. inp and gan are starting to replace sige as the base material in modfets because of their better noise and power ratios.