Interdiffusion: A probe of vacancy diffusion in III-V materials

We have used the interdiffusion of a multiple quantum well sample due to a thin source of vacancies, as a probe, to simultaneously measure the interdiffusion coefficient, diffusion coefficient for group III vacancies in GaAs and the background concentration of these vacancies in a single experiment. We have shown that the interdiffusion at ail temperatures is governed by a constant background concentration of Vacancies in the material and that this background concentration is the concentration of vacancies in the substrate material. The measured vacancy concentration is around 2 x 10(17) cm(-3). This result shows that the vacancy concentrations in GaAs are not at thermal equilibrium concentrations as has been widely assumed. Rather it has value which is ''frozen in,'' probably at the GaAs crystal growth temperature. The activation energy found for the intermixing of InGaAs/GaAs is shown to be governed solely by the activation term for vacancy diffusion which is calculated to have an activation energy of 3.4+/-0.3 eV.