Optimization of QHE-devices for metrological applications

In the framework of an European project aiming at the realization of a syst em for the calibration of capacitance standards based on the quantum Hall e ffect (QHE), optimized QHE: devices for the metrological application as de as well as ac standards of resistance are developed. The present paper desc ribes the de characterization of a large number of devices with different l ayouts, contact configurations, carrier concentrations, and mobilities. The results demonstrate the influence of the device parameters on the critical current, the width of the quantized plateaus, the longitudinal voltages al ong the device and the quantized Hall resistance, Recommendations are given far the layout and mobility of QHE; devices in view of their use as dc sta ndards of resistance.