5 Chemical diffusion in bulk inhomogeneous semiconductors

In this chapter data are listed on chemical diffusion coefficients in bulk inhomogeneous semiconductors. Only data for essentially ‘bulk’ samples are presented. Only technologically important semiconductors are listed in this chapter. The diffusion coefficient which is measured in a chemical composition gradient is usually called the chemical diffusion coefficient or occasionally the mutual or collective diffusion coefficient. Infrequently it may even be called a 'self' diffusion coefficient but this is definitely inconsistent with general usage which reserves the name self diffusion coefficient for the diffusion coefficient measured in a tracer gradient or the latter diffusion coefficient divided by the tracer correlation factor. Where there is diffusion in diffusion couples such as CdS - CdSe (where the chalcogen components move) or CdTe - ZnTe (where both metal components move) the chemical diffusion coefficient is often termed the interdiffusion coefficient. Composition, pre-exponential factor (D ⁰), activation enthalpy (Q), absolute temperature (T-range) data, and methods are tabulated. The methods include electrochemical method, electrical conductivity, growth kinetics method, vapour phase growth, X-ray diffraction method, and vapour phase transport method. A graphical representation of chemical diffusion coefficient, activation energy, pre-exponential factor are shown for Ag_{2 +δ}Te, CdS, CdS-ZnS, CdSe-CdTe, CdTe-HgTe, GaAs-GaP, HgSe-HgTe, HgTe-ZnTe, PbS-PbSe, PbSe-PbTe, PbSe-SnSe, PbTe-SnTe, and ZnSe-ZnTe.