A combination of high resolution Laplace deep level transient spectroscopy (LDLTS) and direct capture cross-section measurements has been used to investigate whether deep electronic states related to interstitial-type defects introduced by ion implantation originated from point or extended defects, prior to any annealing. n-type silicon was implanted with doses of 1×109 cm−2 of silicon, germanium, or erbium, and comparison was made with proton- and electron-irradiated material. When measured by LDLTS at 225 K, the region of the implant thought to contain mostly vacancy-type defects exhibited a complex spectrum with five closely spaced defect-related energy levels, with energies close to EC-400 meV. The region nearer the tail of the implant, which should be dominated by interstitial-type defects, exhibited a simpler LDLTS spectrum with three closely spaced levels being recorded, again with energies centered on EC-400 meV. Annealing at 180 °C did not completely remove any of the defect peaks, suggesting that the energy levels were not due to the simple vacancy-phosphorus center. Direct electron capture cross-section measurements revealed that the defects in the tail of the implanted volume, prior to any annealing, were not simple point defects, as they exhibited nonexponential capture properties. This is attributed to the presence of extended defects in this region. By contrast, defects with the same activation energy in proton- and electron-irradiated silicon exhibited point-defect-like exponential capture.
We have carried out high resolution Laplace deep level transient Spectroscopy (DLTS) and conventional DLTS on silicon implanted with very low doses of either silicon, germanium, erbium, or ytterbium, and compared the results to those from electron-irradiated silicon. DLTS spectra of all the samples initially look very similar, and a peak at 95 K appears in all spectra which may be due to the vacancy-oxygen (VO) defect. We have carried out detailed measurements of the capture cross section and activation energy of this defect using Laplace DLTS. We show that, when the mass of the implanted ion exceeds that of silicon, the defect has a much smaller electron capture cross section than that expected for the VO defect, and a smaller activation energy. Hydrogen has been introduced, either by wet chemical processing or plasma, to all samples to observe the hydrogen–VO interactions resulting in VOH. By using high resolution DLTS we are able to establish that, after hydrogenation, the VOH defect exists with an identical emission rate in the silicon-implanted silicon and the electron-irradiated silicon, but not in the silicon implanted with heavier ions. We conclude that the peak at 95 K in the DLTS spectra in the case of the heavier ions is due to a different defect, confirming earlier reports in the literature. This defect is negatively charged, unlike VO, which is acceptor-like. We are also able to observe VOH in samples where VO is not present, after these samples have been annealed. We attribute this to release of V and H atoms from other defects during annealing.
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