Introduction

Abstract

GaAs transistors have two distinct antages over Si transistors: speed and power. For the same power dissipation, a GaAs circuit is usually faster, and at the same speed, the power in a GaAs circuit is usually lower. The speed advantage comes from the fact that the peak average electron velocity in intrinsic or doped GaAs is several times higher than in Si and it is reached at a much lower value of electric field, and hence with a lower supply voltage. Since the current density in a device is proportional to the electron velocity, the amount of current available to charge or discharge a capacitor in a GaAs device is much larger and the switching speed is therefore higher than in a Si device with the same dimension. In addition, a GaAs field effect transistor does not have any pn-junction around its drain and source terminals and therefore the interelectrode capacitance in a GaAs device is much smaller. Smaller capacitance and higher current density, combined with a smaller voltage swing in a GaAs transistor, contribute to the realization of low-power, high-speed circuits.