Comparison of Be and C diffusion in heavily doped polycrystalline GaAs

The diffusion of Be and C in heavily doped polycrystalline GaAs grown by molecular beam epitaxy and metalorganic chemical vapor deposition has been studied by secondary-ion mass spectrometry and Hall measurement. It is found that Be rapidly diffuses into the undoped buffer layer at a growth temperature of 450 °C. Concentration-depth profiles of Be in AlGaAs/GaAs heterojunction bipolar transistor layers indicate that Be diffuses mainly along polycrystal grain boundaries. On the other hand, C diffusion is negligible even for post-growth annealing at 800 °C. However, annealing increases the resistivity of C-doped GaAs, which is probably due to a change in the occupation site preference of C atoms from As sites.