Carrier Depletion and Grain Misorientations on Individual Grain Boundaries of Polycrystalline Si Thin Films

Structural and microelectrical properties of grain boundaries (GBs) in polycrystalline Si thin films were investigated by electron backscattering diffraction (EBSD) and scanning capacitance microscopy (SCM). The SCM measurements revealed highly nonuniform carrier depletions among the GBs, indicating the variety of electrical properties due to the specific GB structures. The EBSD measurement showed that the films are weakly [001]-oriented with small fractions of grains in the [111] and [110] orientations. Comparison of the SCM and EBSD measurements taken on the same film area led to the following observations: (1) Σ3 GBs do not exhibit carrier depletions and thus do not have charged deep levels; (2) Some Σ9 GBs exhibit carrier depletions and some do not, indicating that the intrinsic Σ9 GBs do not have charged deep levels and the carrier depletions are due to impurity gettering at the GBs; (3) No significant relationship between the carrier depletion behavior and the grain misorientationwas found so far on the GBs with random misorientations; (4) The carrier depletion behavior does not depend only on the grain misorientation but also on the facet where the GB is taken.