Use of molecular beam epitaxy in research and development of selected high speed compound semiconductor devices

Molecular beam epitaxy can fill most of the requirements for high speed III–V compound semiconductor devices. Precise compositon and doping profiles, such as those in selectivity doped heterojunction transistors (SDHT) are examples. The inverted SDHT with the Al,GaAs under the GaAs is a future requirement. High quality, Al,GaAs buffer layers are a general requirement. Conduction band engineering, away from the active layer needs inventive research. The role of the superlattice or other means of improving the buffer needs effort. InP or Al,InAs buffer or confinement layers also need effort, along with improved GaInAs. The requirements of short, ballistic electron FETs, ballistic heterojunction GaAs bipolar transistors, and ballistic injecting and drift transistors will also be reviewed. High current density, exceeding 105 A/cm2, for very high frequency and speed, requires new levels of MBE performance for Ohmic contacts also. The relative merits of GaInAs and GaAs as active materials for high speed devices will also be covered, including applications to high speed photodetectors.