Defect profiling of semiconductor epilayers using positron beams

Over the last 10 years, positrons have been used as a tool to study and profile dilute concentrations of defects in solids. The two basic techniques involve the measurement of the positron lifetime and the Doppler broadening of the annihilation γ-rays. Only recently have positrons been used to profile defects in multilayered structures. We review the theory of positron–defect interactions and positron transport in silicon, and introduce a model used to profile defects and electric-field effects using the steady-state diffusion equation. An example is discussed that involves the modelling of defects and electric fields in homoepitaxial layers of silicon grown by molecular-beam epitaxy on Si(100) substrates. Finally we discuss the limitations of the modelling technique and future prospects.