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MBE grown Er/O doped Si layers can be used for fabricating Si based light emitting diodes that might be developed into an electrically pumped Si laser. The electroluminescence intensity from these layers depends sensitively on the formation of specific types of Er/O precipitates inside the Si host. Hence the microstructure analysis of these layers needs a significant attention to enable an increased efficiency of emission of the devices based on them.
We have performed a detailed microstructure analysis of MBE grown Er/O doped Si layers using electron microscopy and combined it with SIMS measurements as well as electroluminescence studies. Two types of microstructures are observed in different samples with specific Er and O concentrations and grown using Er and Si co-evaporation in an oxygen ambient. The first type of microstructure consists of planar precipitates along (113) planes mostly initiated at the onset of the growth of the Si:Er/O layer. A combination of AFM and TEM analysis reveals that, primarily at the onset of the Er/O doping on Si(001) substrates, the formation of Er/O clusters at the interface disturbs the epitaxial growth at different locations, and this leads to creation of facets along (113) planes with further deposition of Er/O doped Si. The second characteristic type of microstructure observed contain round precipitates of Er/O. Using analytical microscopy techniques it was revealed that the round precipitates contain slightly larger fraction of Er as compared to the planar precipitates of the first type. The planar precipitates normally result in structures with high electroluminescence intensity while the structures with round precipitates have low intensity. The development of the microstructure depends on the Er flux and O pressure as well as the growth rate.
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