Electrical Signature of Ion-Implantation Induced Defects in n-Silicon in the Defect Cluster Regime Studied using DLTS an
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Electrical Signature of Ion-Implantation Induced Defects in n-Silicon in the Defect Cluster Regime Studied using DLTS and Isothermal Transient Spectroscopies Samarendra P. Singh, Vineet Rao, Y. N. Mohapatra, Sanjay Rangan1 & S. Ashok1 Department of Physics, Indian Institute of Technology Kanpur- 208016 INDIA 1 Pennsylvania state university, University Park PA 16802 USA ABSTRACT We study electrical signature of defect clusters in KeV Ar ion-implanted n-silicon using Deep Level Transient Spectroscopy (DLTS) and isothermal capacitance spectroscopies such as time analyzed transient spectroscopy (TATS) and high resolution Laplace-DLTS. The samples are annealed at relatively low temperatures of 350 oC - 600 oC at which defect clusters are known to form and evolve. Contrary to the view that few dominant point-defect like traps are associated with defect clusters, our results show that the band gap may be replete with bands of multiple trap states; however their occupation and hence observation depends on experimental conditions dictated by dynamics of carrier capture and emission at these traps. Charge redistribution among multiple states and deepening of effective emission energy with capture are shown to be commonly occurring at these defects. Isothermal transient spectroscopy is shown to be appropriate tool for recognition of some of these features. INTRODUCTION There is at present a concerted effort to develop methods of obtaining as shallow junction as possible in silicon technology in order to increase the level of integration. It is now well known that the major hurdle in this effort is due to Transient Enhanced Diffusion (TED) [1] of dopants during post-implantation annealing. It is also known that presence of interstitial clusters plays the principal role in this diffusion dynamics. Further, ultimate levels of point defects following thermal processing seem to crucially depend on formation and dissolution dynamics of defect clusters introduced during processing. This focus on defect evolution in post-implantation processes has given rise to an urgent need of characterizing and understanding defect clusters in silicon. Electrical characterization of associated traps is probably the least understood aspect of such clusters [2-4] though it is likely to provide a rich wealth of information regarding their role in controlling various cluster related phenomena. In this paper, we study deep level defects in ion-implanted n-silicon subjected to thermal annealing conditions in which defect clusters are known to form and evolve. We specifically study carrier capture and emission behaviour at the deep levels using DLTS, spectral analysis of isothermal capacitance transients and high resolution Laplace- DLTS. The objective is to investigate the nature of density of states of traps associated with defect clusters. EXPERIMENTAL DETAILS In our search for electrical signature of defect clusters in ion-implanted silicon, we use capacitance based transient techniques such as Deep Level Transient Spectroscopy (DLTS) and Time Analyze
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