Er doping of Si and Si0.88Ge0.12 using Er2O3 and ErF3 evaporation during molecular beam epitaxy - A transmission electron microscopy study

The incorporation behavior of Er into Si and Si0.88Ge0.12 using ErF3 and ER 2O3 as dopant sources during molecular beam epitaxy has been studied. The E r-compounds were thermally evaporated from a high-temperature source. Disso ciation of Er2O3 took place and reaction with graphite parts in the high te mperature source gave an increased CO background pressure and evaporation o f 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 shar p Er concentration profiles were obtained. Transmission electron microscopy analysis shows that it is possible to prepare high crystalline quality str uctures with Er concentrations up to 4x10(19) cm(-3) using Er2O3 and a high F background pressure. Using ErF3 compound as source material a F/Er incor poration ratio of approximately three has been measured by secondary ion ma ss spectrometry. Fluorine incorporation can occur not only from evaporated units of ErF3 molecules, but also from CFx (x = 1-4) and F background speci es, which are present due to a reaction between the ErF3 source material an d the graphite crucible in the source. After careful degassing of the sourc e, 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 degrees C) and undoped layers grown at a higher temperature (630 degrees C), a flat surface could be maintained d uring the growth sequence. In this way it was possible to prepare Er-doped structures with an average Er concentration of 1 x 10(19) cm(-3) and withou t observable defects using ErF3 as source material. For the case of Er-dopi ng of Si0.88Ge0.12 using ErF3, we observed contrast along lines in the grow th direction at an Er concentration of 1 x 10(19) cm(-3), which was attribu ted to Si concentration variations. Intense emission related to Er has been observed by electro- and photoluminescence. (C) 1999 Elsevier Science B.V. All rights reserved.