Annealing studies of highly doped boron superlattices

Abstract

Coevaporation of B2 O3 during silicon molecular-beam epitaxy at growth temperatures (TG ) 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 TG >700 °C and high boron concentrations. In addition, significant oxygen was incorporated for TG ≤700 °C, with a growth rate of 0.5 nm s−1 and a B2 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 TG.