Self-Diffusion in Isotopically Controlled Heterostructures of Elemental and Compound Semiconductors

Abstract

We report self-diffusion studies of silicon between 855 and 1388°C in highly enriched epitaxial ²⁸Si layers. Diffusion profiles of ³⁰Si and ²⁹Si are determined with high resolution secondary ion mass spectrometry (SIMS). The temperature dependence of the Si self-diffusion coefficients is accurately described with an activation enthalpy of 4.76 eV and a pre-exponential factor of 560 cm²s^-1. The single activation enthalpy indicates that Si self-interstitials dominate self-diffusion over the whole temperature range investigated. Self- and interdiffusion in buried Al⁷¹GaAs/Al⁶⁹GaAs/⁷¹GaAs isotope heterostructures with different Al composition is measured between 800 and 1160°C. Ga self-diffusion in AlGaAs and interdiffusion of Al and Ga at the AlGaAs/GaAs interface show that Ga diffusion decreases with increasing Al composition and that the interdiffusion coefficient depends linearly on Al concentration. Furthermore Al is found to diffuse more rapidly into GaAs than Ga diffuses in GaAs. The temperature dependence of Ga and Al diffusion in GaAs and of Ga diffusion in AlGaAs is described by a single activation enthalpy in the range of 3.6±0.1 eV, but by different pre-exponential factors. Differences found for Ga and Al diffusion in GaAs and for Ga diffusion in AlGaAs with different Al concentrations are discussed.