engleski

Vacancy cluster formation in implanted and in neutron irradiated germanium

During implantation and implantation anneals germanium behaves very differently to silicon. In general the concentration of implantation defects is considerably higher but perhaps the most striking difference is the formation of relatively stable defects which seem to play a role in limiting the electron concentration to much lower levels than those necessary for extremely scaled nMOS. There is strong evidence that these defects are related to vacancy reactions. In this paper we consider the mechanisms which may lead to the formation of such defects using a Monte Carlo simulation of the implantation in conjunction with consideration of coulombic effects during implantation and annealing. Using experimental results derived from DLTS and positron annihilation experiments on self implanted and on neutron irradiated germanium we consider the kinetics of how such clusters may form and conclude that localized type inversion at the end of range plays a key role in the formation of these cluster defects. Possible scenarios for inhibiting the cluster formation are considered including the incorporation of impurities which may act as vacancy traps and the use of thermal treatments which minimize the time spent at temperatures favorable for specific cluster reactions.

defects; germanium; neutron irradiation; dlts

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