High electron mobility transistor

A semiconductor device, comprising:

• a substrate having an upper major surface and a lower major surface;
• a channel layer having an upper major surface and a lower major surface and provided on the upper major surface of the substrate, said channel layer comprising an undoped first group III-V compound semiconductor material having a first lattice constant and containing indium arsenide as a component, said first group III-V compound semiconductor material having a first conduction band characterized by a first energy level at the upper major surface of the channel layer and a first valence band characterized by a second energy level at the upper major surface of the channel layer such that the second energy level is separated from the first energy level by a first band energy gap;
• a two-dimensional electron gas formed in the channel layer along the upper major surface thereof as a substantially scatter-free path of electrons;
• an electron supplying layer having an upper major surface and a lower major surface and provided on the upper major surface of the channel layer so as to form a heterojunction interface between the upper major surface of the channel layer and the lower major surface of the electron supplying layer, said electron supplying layer comprising a second group III-V compound semiconductor material having a second lattice constant and doped to the n-type by a doping of impurity atoms and supplying electrons to the channel layer to form the two-dimensional electron gas therein;
• source electrode means provided on the upper major surface of the electron supplying layer for injecting electrons into the electron supplying layer;
• drain electrode means provided on the upper major surface of the electron supplying layer for collecting electrons from the electron supplying layer;
• and
• gate electrode means provided on the upper major surface of the electron supplying layer for controlling the passage of the electrons in the two-dimensional electron gas;
• said second group III-V compound semiconductor material having a second conduction band characterized by a third energy level at the lower major surface of the electron supplying layer and a second valence band characterized by a fourth energy level at the lower major surface of the electron supplying layer such that the fourth energy level is separated from the third energy level by a second band gap, said second group III-V compound semiconductor material having a composition determined such that the second lattice constant matches to the first lattice constant so that the passage of the electrons through the two-dimensional electron gas occurs substantially identical with a case wherein the first and second lattice constants are identical with each other, and such that the first energy level of the first conduction band is located at an energetically lower level than the fourth energy level of the second valence band;
• said second group III-V compound semiconductor material being doped by the impurity atoms to a concentration level such that the Fermi level is located between the third and fourth energy levels of the second group III-V compound semiconductor material.