| 摘要 |
PURPOSE:To obtain an FET with low noise and high operation speed by a method wherein an AlGaAs layer, which is an electron supply source of the hetero-junction type FET, is composed of a superlattice structure to realize high electron concentration. CONSTITUTION:A high-purity and non-doped GaAs layer 12 and an AlGaAs superlattice layer 13 are laminated on a semi-insulating GaAs substrate 11 and a source electrode 14a, a gate electrode 14b and a drain electrode 14c are provided. The superlattice layer is composed of repetitive structure of a non-doped Al0.4Ga0.8As layer 15, a non-doped Al0.2Ga0.8As layer 16 and an N-type Al0.2Ga0.8As layer 17 whose thicknesses are about five atoms thick respectively. The N-type AlGaAs layer is an electron supply source and if the layer can supply electrons with higher concentration, the characteristics of the element can be better. The Al mixed crystal ratio (x) is selected to be less than 0.2 in the layer 17 doped with donors and, in the layer 15, x 0.4 to increase the actual mixed crystal ratio of the superlattice and the layer 15 is not doped and, in the layer 16, x=0.2 to make the layer 16 serve as a buffer layer for protecting the donors from the influence of the layer 15. With this constitution, most of the donor electrons added to the layer 17 are activated in the conduction band and the electron concentration of about 10<19>cm<-3> can be obtained for the whole layer 13 so that an FET with low noise and high operation speed can be obtained. |
