Abstract
The resistance change due to piezoelectric charge densities in n-GaAs mesa resistors has been studied as a function of surface stress. Those changes are verified by measuring some realized stress transducers with such resistors fabricated on the surface of micromachined thin GaAs membranes or GaInP/GaAs cantilever beams. It is shown here that the surface stresses induced by the deformation of cantilever beams can cause nonuniform stress distributions within the resistors, and the stress gradients consequently yield considerable piezoelectric charge densities that lead to an appreciable resistance change. In addition, this effect of piezoelectric charges is examined from several types of resistors that have a different doping, direction, thickness h, and width-to-thickness ratio L/h. According to those results, optimization of this mechanism is related to the doping and geometrical design of GaAs mesa resistors. In addition to the effect of piezoelectric charges, mobility change can affect the resistance as well. The resistance changes observed from the low doped resistors exhibit an opposite sign for the resistors oriented along [011] and [011̄] directions. These directional-dependent characteristics confirm that the effect of piezoelectric charges indeed exists in mesa resistors. Fitting the width-dependent sensitivities measured in experiments allows us to estimate each contribution of these two effects. For the [011̄] oriented resistors with L/h of 10, and ns of 4.8×1011, the sensitivity of relative resistance change as high as 92.7%/GPa is obtained. Results in this study demonstrate that the resistance change in n-GaAs mesa resistors is attributed to the effects of piezoelectric charges and mobility change. Moreover, GaInP/GaAs material system with its piezoresistive response originated from piezoelectric charges is highly promising in III–V compound semiconductor stress transducers.
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