The realization of a GaAs—Ge wide band gap emitter transistor

The fabrication and properties of an n-GaAs emitter, p-Ge base, n-Ge collector transistor which possesses significant current gain is described, These GaAs wide band gap emitter transistors have shown incremental current gains near 15 when operated at current densities up to 3500 A/cm². The doping level used in the base region was quite high (up to 5×10¹⁹/cm³in order to avoid a spurious Ge p-n junction in this region. The epitaxial deposition of the GaAs emitter region was carried out at a low temperature in order to also avoid a hidden p-n Ge junction. The low deposition temperature resulted in low (about 5×10¹⁵/cm³emitter doping levels. The general nature of the GaAs-Ge heterojunction energy-band diagram permits this high doping in the base or Ge region relative to the GaAs emitter region without reducing the current gain below unity. The observation of gain in this n-p-n heterojunction structure where the emitter is much more lightly doped than the base is considered to be confirmation of the theoretical proposals of Shockley and Kroemer.