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Fabrication of a Si Nanometer Column PN Junction and Implanted Defect Evaluation by Transmission Electron Microscopy

We have proposed a Si nanometer column 1-D PN junction which allows electrons to tunnel between P- and N-regions across a depletion region. In order to observe the 1-D tunneling effect, heavy doping with both P- and N-type impurities is necessary. The present work investigated elimination of defects caused by ion implantation in the fine Si columns which were less than 50 nm in diameter by TEM. In the case of heavy doping with As or BF2 the as-doped structure is amorphous, and recrystallization is observed after annealing at temperatures above 600°C. Typical defects such as dislocations which are parallel to the {111} planes, twins which are formed on the {111} planes, and Si microcrystals which are differently oriented from the Si bulk of the substrate are observed in Si columns with diameters of larger than 20 nm. No defects are observed in ultrafine Si columns with diameters of less than 20 nm. It is suggested that defects formed during ion implantation diffuse to the surface or the Si/SiO2 interface of the ultrafine Si columns during annealing. The results indicate that it is possible to fabricate a 1-D PN junction with no defects.