THE COMPOSITIONAL HOMOGENEITY AND ELECTRONIC PROPERTIES OF SINGLE CRYSTAL SEMICONDUCTORS DEPEND ON THE DIFFUSION COEFFICIENTS OF IMPURITIES AND DOPANTS DISSOLVED IN THE MELT. HOWEVER EVEN AFTER SEVERAL DECADES OF RESEARCH THE PUBLISHED VALUES OF DIFFUSION COEFFICIENTS CAN VARY SIGNIFICANTLY. DIFFUSION IS A SLOW PROCESS AND THUS AFFECTED BY MINUTE LEVELS OF CONVECTION. THUS IT IS EXPECTED THAT PREVIOUS MEASUREMENTS OF DIFFUSION HAVE BEEN COMPROMISED BY NATURAL OR BUOYANCY-DRIVEN CONVECTION WHICH IS UNAVOIDABLE ON EARTH. MICROGRAVITY PRESENTS AN OPTIMAL ENVIRONMENT TO OBTAIN HIGH-FIDELITY DIFFUSION DATA. THIS DATA IS ESSENTIAL FOR THE COMPUTER MODELS WHICH ARE USED TO OPTIMIZE INDUSTRIAL CRYSTAL GROWTH PROCESSES. THE KEY GOALS OF THIS PROPOSAL ARE AS FOLLOWS: (I) DEVELOP AND CALIBRATE A PROCESS TO MEASURE DIFFUSION COEFFICIENTS ON EARTH (II) USE THIS PROCESS TO MAKE ACCURATE MEASUREMENTS OF DIFFUSION COEFFICIENTS IN GE IN MICROGRAVITY (III) USE THIS PROCESS TO MEASURE THE DIFFUSION COEFFICIENTS OF IMPURITIES IN SI MELTS.