Si Ge& GaAs Technological evolution began with gemanium in 1940s Band gap e =0.67eV At 300 K, intrinsic carrier density n; =2.5 x 1013 cm-3 n; arises fast with T, due to sm-ig1015 cm-3 at 400 K Device not useful when intrinsic carrier concentration is comparable to dopant density Research efforts shifted to silicon(Ea=1.12 ev) and GaAs(ea=1.42 e) in 1950sSi, Ge & GaAs • Technological evolution began with gemanium in 1940s. – Band gap Eg = 0.67 eV – At 300 K, intrinsic carrier density ni = 2.5 x 1013 cm-3 – ni arises fast with T, due to small Eg – ~1015 cm-3 at 400 K – Device not useful when intrinsic carrier concentration is comparable to dopant density. • Research efforts shifted to silicon (Eg = 1.12 eV) and GaAs (Eg = 1.42 eV) in 1950s