High Speed Microwave and Optoelectronic Devices

Modulation-doped field effect transistors (MODFET's) have become the most highly developed microwave and millimeter wave semiconductor devices. Using pseudomorphic InyGal-yAs channels, with y 5 .25 and atomic planar doping in the Alfial-xAs barriers, with x 5 -30 high frequency, high power, and high efficiency have been achieved on .GaAs substrates. Using InyGal-yAs channels, with y = .53 or somewhat higher, and atomic planar doping in the InxAll-xAs barrier, with x 1. .52, very high frequency and very low noise performance has been achieved on InP substrates. In such structures there is a potential step in the conduction band, A E C , which confines an electron sheet to the low bandgap material, forming a dipole with the donors, in the larger bandgap barrier, separated by a thin spacer layer from the electrons.