Annealing studies of highly doped boron superlattices

Coevaporation of B₂ O₃ during silicon molecular-beam epitaxy at growth temperatures (T_G) varying from 540 to 800 °C has been used to prepare superlattice structures (pipi's) of varying boron concentration (3×10¹⁸ -3×10²⁰ B cm ^-3). The superlattices were subsequently subjected to various annealing procedures and the layers were examined by secondary ion mass spectrometry, electrochemical profiling, and cross-sectional transmission electron microscopy. A significant redistribution of boron was observed even before annealing for T_G >700 °C and high boron concentrations. In addition, significant oxygen was incorporated for T_G ≤700 °C, with a growth rate of 0.5 nm s^-1 and a B ₂ O₃ flux of 2×10¹³ cm^{- 2} s^-1. After annealing, the boron diffusion coefficients were determined for the layers and found to vary significantly with T_G.