Abstract
Single‐crystal wafers grown by both the vertical gradient freeze (VGF) technique and the liquid encapsulated Czochralski (LEC) have been studied and compared in terms of overall quality. The techniques used to characterize the defect structure consist of (i) defect‐revealing etch, (ii) transmission x‐ray topography (TXRT), and (iii) transmission cathodoluminescence (TCL). Subsequent to etching, the VGF substrates were found to have a uniformly low (<100/cm2) EPD from the wafer edge to the center with no slip observed. The low defect density is independent of the sulfur doping level in the range and is attributed to the reduced axial and radial temperature gradients during growth. In contrast, the Sn‐ and Fe‐doped LEC material had overall EPD levels exceeding 104/cm2. For heavily sulfur‐doped LEC material considerable slip and dislocations remain at the periphery. The TXRT studies of the VGF material show large areas (>10 cm2) that are dislocation free, whereas the LEC material shows dislocation tangles even in the relatively low EPD region. TXRT and TCL reveal the growth striations due to nonhomogeneous dopant incorporation. In the case of the LEC material, they are strongly concave, indicating a nonplanar liquid/solid growth interface and there is sharp contrast in the striations due to large fluctuations in dopant incorporation. The VGF striations are found to be planar and show very weak contrast.
Published Version
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