Microwave Photoconductivity Measurements to Characterize Semiconductors
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MICROWAVE PHOTOCONDUCTIVITY MEASUREMENTS TO CHARACTERIZE SEMICONDUCTORS M. KUNST Hahn-Meitner Institut, Solare Energetik, D - 1000 Berlin 39, West Germany.
ABSTRACT After a general survey of characterization techniques the use of transient photoconductivity measurements in the microwave frequency range for the characterization of semiconductors and semiconductor devices for (opto)electronic applications is treated. Experimental details and applications of these measurements are given.
INTRODUCTION The semiconductor industry has an urgent need for methods that enable an effective quality control. In particular control of the starting material of many semiconductor devices, semiconductor wafers, seems very important because the use of inferior material will lead to a device of bad quality. However, also the control of different steps during the production of devices by an in-situ characterization method is of eminent importance ( this may also lead to improvement of production steps ). To this purpose non-evasive and contactless methods to characterize semiconductors seem to be appropriate. It is evident that the process that mainly determines the performance of this kind of devices is charge carrier kinetics. This suggests that techniques monitoring a property related to charge carrier kinetics will be extremely useful to characterize semiconductors. In this work the characterization of semiconductors and semiconductor devices for (opto)electronic applications by contactless (transient) photoconductivity measurements in the microwave frequency range is discussed.
METHODS TO CHARACTERIZE SEMICONDUCTORS The characterization of semiconductors and semiconductor devices for (opto)electronic applications must obviously proceed by measurement of one or more parameters related to the (opto)electronic properties of the material. The choice of the most appropriate parameter is determined by the quantity and the quality of the information given by this parameter on the performance of the system investigated. Besides, the determination of this parameter must be as easy as possible. It is clear that the parameter appropriate for all devices and for all applications does not exist and that optimal characterization is relatively specific for a particular device and its application.
Mat. Res. Soc. Symp. Proc. Vol. 189. 01991 Materials Research Society
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For (opto)electronic devices it seems obvious to start with charge carrier kinetics as the fundamental process determining the performance of these devices. So measurable properties of one or more of the species participating in charge carrier kinetics may be used for characterization. From an experimental point of view it is often more easy to measure the change of a property than the property itself. This suggests measurements of excess charge carrier kinetics. Besides, it must be remarked that the action of all optoelectronic devices and most electronic devices relies more on excess carrier kinetics than on carrier kinetics. The most appropriate way to perturb carrier kin
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