A piezotransistor concept for measuring transient pressures in combustion engines at high temperatures using the transversal piezoelectric effect in (100) GaAs is presented. The sensor was used without cooling to measure the pressure in a combustion chamber for a motored and fired engine. The results which are presented here are in good agreement with the signal from a commercial quartz sensor, which needs an additional preamplifier. Such an active GaAs sensor is therefore a very attractive alternative to the commonly used quartz sensors for dynamic pressure measurements at high temperatures. Compared to quartz sensors the GaAs sensor has the advantage of a possible integration of electronics on the sensor chip.
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samples have been exposed to an RF‐excited hydrogen plasma for different power levels with variation of the substrate dc bias‐voltage. At negative and low positive bias‐voltages, depending on the RF power, surface damage is caused by bombardment of high‐energy positive ions. Increasing the bias‐voltage reduces the damage and the application of one particular bias‐value can prevent a change in carrier concentration after plasma exposure. For higher positive bias‐voltages the resulting carrier concentration towards the surface decreases again, this effect being probably due to bombardment of negative ions or a surplus of phosphorus ions at the sample surface. The investigations show that the ion energy is a critical parameter in plasma cleaning procedures of semiconductors and that a hydrogen plasma can be used to clean
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substrates for epitaxial growth, if an appropriate bias‐voltage is applied to the substrate, in order to prevent surface damage.
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