IV. Applications to solid state physicsImplantation and channeling effects of alkali ion beams in semiconductors☆
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AbstractIon beams of K+ and Cs+ in an energy range from 1–20 keV have been employed in a study of penetration, channeling and type conversion in targets of oriented single crystal semiconductors, particularly silicon. The alkalis form n-type impurities in silicon. Targets of p-type silicon over a wide resistivity range have been used to study type conversion and junction formation effects.Target resistivity, crystallographic orientation, energy and target temperature are important parameters in determining the profile of the implanted species and the junction depth, XJ.The effects if crystallographic orientation on junction depths (determined directly by angle/section and stain techniques) are strongly suggestive of a channeling process. The order of penetrability is 〈 110 〉 > 〈 111 〉 ≳ 〈 100 〉. and the sheet resistance of the implanted layers is consistently smaller for the transparent directions. The variation of junction depth with the energy of the ion is not as important as its dependence on the target temperature of crystallographic orientation (with the velocity of the ion rather than its energy being the determinant factor for measured values of XJ). The magnitude of the channeling effect is strongly temperature dependent. Concentrations of electrically active species in targets implanted by potassium are an order of magnitude higher than those achieved with cesium implantation under similar conditions. The profile of the electrically active species appears to have two parts; there is a layer of high concentration and relatively steep gradient followed by a persistent straggling tail.

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