Laser beam induced currents in polycrystalline silicon thin films prepared by interference laser crystallization

Polycrystalline silicon layers are prepared by interference laser crystallization (ILC) in the superlateral growth regime. To characterize their microscopic photoelectrical properties, light beam induced current (LBIC) is used, employing a focused laser beam for local generation of photocarriers in the layers with spatial resolution of ≈0.4 μm. The results are correlated with surface morphology obtained by atomic force microscopy. In the single pulse ILC, the temperature profiles are optimized by changing the proportion of interfering beam intensities. The typical grains are of triangular shape, with a length of 1.5 μm and width <0.5 μm. The photocurrent response is dominated by variations in the sample thickness. In the multiple pulse ILC, thin films with grains of quadratic shape and of size exceeding 5 μm are obtained by shifting the sample through an interference pattern, thus taking advantage of lateral epitaxial regrowth. Here, by use of a lock-in, LBIC can detect position and local electronic properties of individual grain boundaries. Grain boundaries are clearly identified by 180° shifts of the photocurrent phase close to maxima of photocurrent amplitude. The photocurrent is attributed to local fields at grain boundaries. These fields extend about 1.4 μm into the grains. The barrier height at the boundary is about 110 mV.