Er doping of Si and Si 0.88Ge 0.12 using Er 2O 3 and ErF 3 evaporation during molecular beam epitaxy A transmission electron microscopy study

Abstract

The incorporation behavior of Er into Si and Si 0.88Ge 0.12 using ErF 3 and Er 2O 3 as dopant sources during molecular beam epitaxy has been studied. The Er-compounds were thermally evaporated from a high-temperature source. Dissociation of Er 2O 3 took place and reaction with graphite parts in the high temperature source gave an increased CO background pressure and evaporation of metallic Er. Surface segregation of Er may be strong, but with a high CO or F background pressure, the surface segregation could be reduced and sharp Er concentration profiles were obtained. Transmission electron microscopy analysis shows that it is possible to prepare high crystalline quality structures with Er concentrations up to 4×10 19 cm −3 using Er 2O 3 and a high F background pressure. Using ErF 3 compound as source material a F/Er incorporation ratio of approximately three has been measured by secondary ion mass spectrometry. Fluorine incorporation can occur not only from evaporated units of ErF 3 molecules, but also from CF x ( x=1–4) and F background species, which are present due to a reaction between the ErF 3 source material and the graphite crucible in the source. After careful degassing of the source, the partial pressures of these species can be significantly reduced. By producing an Er-doped multilayer structure consisting of alternating doped layers grown at low temperature (350°C) and undoped layers grown at a higher temperature (630°C), a flat surface could be maintained during the growth sequence. In this way it was possible to prepare Er-doped structures with an average Er concentration of 1×10 19 cm −3 and without observable defects using ErF 3 as source material. For the case of Er-doping of Si 0.88Ge 0.12 using ErF 3, we observed contrast along lines in the growth direction at an Er concentration of 1×10 19 cm −3, which was attributed to Si concentration variations. Intense emission related to Er has been observed by electro- and photoluminescence.