Native Oxide Layer Role during Cryogenic-Temperature Ion Implantations in Germanium

Abstract

Herein, the structural properties and chemical composition of Ge samples implanted with tellurium at cryogenic temperatures are analyzed, focusing on the role of the native oxide. For germanium, cryogenic-temperature implantation is a requirement to achieve hyperdoped impurity concentrations while simultaneously preventing surface porosity. In this work, the critical role of the thin native germanium oxide is demonstrated when performing ion implantations at temperatures close to the liquid nitrogen temperature. The structural and chemical composition of tellurium-implanted samples as a function of the implanted dose from 5 × 1014 to 5 × 1015 cm−2 is analyzed. After a laser melting process, the incorporated oxygen is diffused to the surface forming again a GeOx layer which retains a large fraction of the total implanted dose. These detrimental effects can be eliminated by a selective etching of the native oxide layer prior to the ion implantation process. These effects have been also observed when implanting on Si substrates. This work identifies key aspects for conducting implantations at cryogenic temperatures, that are otherwise negligible for ion implanting at room temperature.