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GaAs has been grown by molecular‐beam epitaxy on both silicon and silicon on sapphire. The incorporation of a low temperature buffer has reduced the film stress from 3.0 to 2.2 kbar for GaAs grown on silicon. However, films stress can be completely removed for growth of GaAs with the incorporation of the low temperature buffer when grown on silicon on sapphire (SOS). The orientation dependence of GaAs grown on SOS has been investigated by growing on orientations slightly off axis from the (100) in the [011] direction by 2°, 4°, and 6°. X‐ray, mobility and photoluminescence measurements have been made, showing that growth on 6° misoriented SOS produces nearly stress free films, with materials properties similar to those of GaAs on silicon, and mobilities six times higher than those of GaAs grown on on‐axis (100) SOS. Metal–semiconductor field effect transistors (MESFETs) have been fabricated on GaAs on silicon showing device characteristics comparable to those of GaAs on GaAs.

Defect free strained layer epitaxy opens possibilities for further improvement on the quantum well two‐dimensional electron gas (TEG) structures grown using the GaInAs/AlInAs on InP materials system. Increased freedom with composition allows for optimizing certain properties of the structure, such as, the conduction edge discontinuity which controls the maximum sheet concentration (ns); and the electron effective mass which influences the speed of the structure. These enhancements can be made, respectively, by increasing the Al concentration in the AlInAs and/or by decreasing the Ga concentration in the GaInAs. The maximum amount of strain which can be incorporated into the unrelaxed material sets an upper limit on the compositional tolerances. The tolerances will be shown to be large for the AlInAs and the active TEG GaInAs region. The compositions are obtained using the intensity oscillations observed in the reflective high‐energy electron diffraction (RHEED) specular beam during growth of GaAs, AlAs, a...

Ga0.47In0.53As–Al0.48In0.52As high‐electron mobility transistors (HEMT’s) exhibit high transconductance and gain because of the high conductivities achievable in the structures. The effect of epitaxial layer design (spacer thickness and active channel thickness) on conductivity is examined. Device characteristics are examined as a function of active channel thickness. Reduced output conductance is observed for a 200 A channel, but with a reduced transconductance.