Sidegating reduction for GaAs integrated circuits by using a new buffer layer

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Side-gating effects relevant to GaAs digital, analog, and monolithic microwave integrated circuits have been significantly reduced or eliminated by using a high-resistivity GaAs buffer layer grown at low substrate temperatures by molecular beam epitaxy (MBE). The high resistivity of the low-temperature (LT) GaAs buffer is attributed to an arsenic excess of approximately 1 at.%. For analog ICs operating at intermediate frequencies, the LT GaAs buffer eliminates the resistive component of RF coupling. The higher the frequency, the smaller the improvement in performance afforded by the LT GaAs buffer, because capacitive coupling increasingly dominates resistive coupling. The dependence of drain current on the duty cycle of an adjacent digital signal is also eliminated by using the LT GaAs buffer. At microwave frequencies, the LT GaAs eliminates the variation of MESFET equivalent circuit parameters with side-gate bias. Thus the restrictions on device and circuit layout currently imposed by side-gating can be eliminated. >