Silicon substrate optimization for microwave applications of GaAs/Si MESFETs

Silicon substrates were cut at tilt angles ranging from 0 to 9 ° off the (100) plane, and heteroepitaxial GaAs layers were grown by molecular beam epitaxy (MBE). The d.c. and RF performance of MESFET devices defined on these layers was used as a measure of the optimum substrate tilt angle. Best performance was observed between 3 and 4.5 ° tilt. MESFET device performance was also compared as silicon substrate resistivity was varied from 10−3 to 103 Ω cm. A minimum resistivity of 10 Ω cm is found to be necessary for high performance heteroepitaxial MESFET devices. No effect of substrate conductivity type on device performance was observed.