Some Possibilities of Using Defects for Applications in Semiconductors
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SOME POSSIBILITIES OF USING DEFECTS FOR APPLICATIONS IN SEMICONDUCTORS Michel LANNOO I.E.M.N. (UMR CNRS N0 9929), D~partement ISEN, 41, boulevard Vauban, 59046 LILLE CEDEX
ABSTRACT Specific situations where defects have a positive impact on the properties of semiconductors are examined. In a first category are ranged defects used as probes for characterizing materials. Then semiconductors with high concentration of defects like low temperature GaAs and porous Si are discussed. This is followed by cases where direct use is made of the defect properties (optical, pressure ... ). Finally several possibilities for defect engineering of materials are reviewed. I. INTRODUCTION It has been known for a very long time that, under suitable conditions, defects or impurities can modify in a positive way the properties of semiconductor materials. Trivial examples are donor and acceptor impurities in bulk semiconductor crystals which are at the basis of their usefulness in devices. Another interesting case is provided by hydrogen passivation of amorphous silicon which, by saturating the existing dangling bonds, has allowed for doping of such material. Over the years there has been such progress in semiconductor technology that defects are now mostly considered as undesirable. However, at the same time, there has also been great progress in the understanding and control of point defects and it should be of major interest to use this knowledge for improving and even monitoring the properties of materials, leading to what can be called defect engineering. The aim of this talk is to describe several situations where this can be achieved, using varying aspects of defect properties. No attempt is made to perform a complete review. It is however hoped that this can convince the reader that the controlled use of defects can be one of the tools for realizing better materials for increased device performance. II. DEFECTS AS PROBES FOR THE CHARACTERIZATION OF MATERIALS We consider here situations in which the specific properties of defects can be used to probe the properties of materials. A first interesting example corresponds to the possibility of predicting band offsets from the known position of defect energy levels. It was noticed by Langer and Heinrich [1] that, in isovalent semiconductors, one can align the energy levels of all transition metal impurities (T.M.) simply by a rigid shift of their band structure. This is shown on fig. 1 for the Ill-V materials. The resulting shift can be thought to give the natural band offset for the materials. The predicted offsets show fairly good Mat. Res. Soc. Symp. Proc. Vol. 262. 01992 Materials Research Society
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