Interdiffusion in GaAs bipolar structures

Emitter, base, and collector layers of GaAs with a nominal thickness of 0.5 μm each were grown by organometallic vapor phase epitaxy (OMVPE). Each layer contained concentration spikes of the interdiffusion marker, indium. Annealing was performed in an open tube system for 1 h at T=900°C using a controlled arsenic pressure. The dopants used, tellurium and carbon, reside on the group V sublattice and they are not expected to induce the so-called kick-out diffusion mechanism. The measured interdiffusion results are consistent with native defect concentrations´ which approach their equilibrium values during the annealing process. A small emitter push effect can be measured for npn structures. We find that a Ga vacancy, with a charge of -1, provides a consistent explanation for interdiffusion in both n-type and p-type GaAs over the range of carrier density n=1×10¹⁹ cm^-3 to p=1×10¹⁹ cm^-3