MICROSEGREGATION IN CONVENTIONAL SI-DOPED LEC GAAS

The dopant distribution in [100] Si-doped GaAs was quantitatively analyzed using NIR transmittance measurements with a spatial resolution of better than 2-mu-m. Microsegregation inhomogeneities, in the form of striations, are found to be random and discontinuous; they are identified predominantly as abrupt dopant concentration decreases resulting from temporal, localized back melting associated with turbulent convection in the melt. Variations in free charge carrier density associated with the striations approach in many instances two orders of magnitude and are thus by a factor of ten larger than anticipated and reported in the open literature for Si and Ge. Periodic striations normally associated with rotational crystal pulling are absent.