Bulk Defects and Radiation Damage in Detector Grade Silicon
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BULK DEFECTS AND RADIATION DAMAGE IN DETECTOR GRADE SILICON
J. WALTER AND W. GARBER, IntraSpec, Inc.*, Oak Ridge, TN R. WUNSTORF AND W. BUGG, University of Tennessee, Knoxville, TN J. HARVEY and W. CASSON, Oak Ridge National Laboratory-, Oak Ridge, TN
ABSTRACT The importance of bulk defects in Si to the performance of Si radiation detectors is discussed and the current state of knowledge about deep level defects, including those induced by radiation damage, is briefly reviewed. The importance and origins of the fluctuations in the spatial distribution of the shallow point defects which determine the uncompensated net impurity density are discussed and information on this problem in FZ silicon, multipass FZ silicon, neutron transmutation doped Si, and radiation damaged Si is presented and compared to what should be expected on the basis of simple modeling. A new model for radiation damage induced changes in the net uncompensated impurity density is reviewed and compared to experimental data on fast neutron damage in Si.
INTRODUCTION Bulk defects have dominated the performance of silicon radiation detectors since their inception. Unlike the case of Ge, little dedicated work has been done on improving the quality of Si for radiation detectors; with most of the progress coming from Si crystal technology improvements for other applications. With the growing need for large scale applications of Si detectors in elementary particle physics research, there has been a renewed interest in improving the cost and quality of detector grade Si and in bulk radiation damage problems in Si detectors. The superior characteristics of Si detectors make them the best performance choice for many particle physics applications. However, the background radiation in high luminosity accelerators is quite intense. Therefore, radiation damage and detector cost will determine the extent to which Si is used for these large scale applications. Since these new types of detectors may cover the entire surface of a 100 mm diameter wafer, the issue of spatial uniformity of the material properties has also become an issue of considerable interest. Defects which produce deep levels can be the source of excess leakage current related noise or can act as charge traps which degrade the integrity of the pulse height response. Shallow levels which act as thermal donors and acceptors establish the uncompensated impurity level and thereby establish the maximum detector sensitive depth that can be obtained with a reasonable reverse bias voltage. In the following, we briefly review the detector related problems of deep level defects in float zone (FZ) Si and radiation damaged Si. We then present some recent work on shallow donors and acceptors and their spatial distribution in single and multipass FZ Si crystals, neutron transmutation doped (NTD) Si, and Si with bulk radiation damage.
Mat. Res. Soc. Symp. Proc. Vol. 302. @1993 Materials Research Society
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DEEP LEVEL DEFECTS Generation/ Recombination Current Defects which produce levels near the center of
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