tailieunhanh - Diffusion Solids Fundamentals Diffusion Controlled Solid State Episode 2 Part 7

Tham khảo tài liệu 'diffusion solids fundamentals diffusion controlled solid state episode 2 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Germanium 401 Fig. . Doping dependence of Ge self-diffusion according to Werner ET al. 12 - Further information about the nature and properties of point defects involved in the diffusion process has been deduced from the effect of pressure on diffusion see Chap. 8 . Measurements of Ge self-diffusion under pressure are reported in 12 . The activation volumes are comparatively small and vary from to atomic volumes Q as the temperature increases from 876 to 1086 K Fig. . Values of the activation volume for self-diffusion of gold are shown for comparison 14 . These larger values are typical for vacancy-mediated diffusion in close-packed metals. The lower values for Ge support the concept that self-diffusion in Ge occurs via vacancies which are more relaxed or spread-out than in close-packed materials. The positive sign very likely excludes self-interstitials as the defects responsible for Ge self-diffusion. For an interstitialcy mechanism the activation volume should be negative see Chap. 8 . The experimental activation volume increases with temperature. This increase can be attributed to the fact that neutral and negatively charged vacancies with differnet activation volumes contribute to self-diffusion. The activation volume of the neutral vacancy contribution AVy0 Q is larger than that of the negatively charged vacancy AVy- Q 12 . The experimental activation volume is an average value weighted with the relative contributions of the two types of vacancies to the total self-diffusivity ĩ r. AV AVy0Ĩ AVy-i-D- . Since the contribution of charged defects becomes more significant with decreasing temperature the effective activation volume decreases. 402 23 Self-diffusion in Elemental Semiconductors 300 900 T C 500 700 g s 0 500 700 900 1100 T K Fig. . Activation volumes of Ge self-diffusion according to Werner ET AL. 12 . For comparison activation volumes of Au self-diffusion are also shown 14 Silicon .