Observation of Geometry Induced Doping in Thin Si Nano-grating Layers

Abstract We fabricate Si nano-grating layers and measure their electrical characteristics to monitor geometry induced doping. SOI device layer was thinned down by thermal oxidizing and subsequent wet etching of the oxide. Grating was fabricated using laser interference lithography (375 nm laser) followed by reactive ion etching of Si. Next, large square island (0.5x0.5 mm) was shaped in the device layer and four Si\Ti\Ag ohmic contacts were formed to measure electrical characteristics. The I-V characteristics were recorded using both 4 wire and 2 wire methods. Resistance-temperature dependences (T= 4-300 K) were recorded as well. For all 12 samples, nano-grating layers show 2-3 order reduction of resistivity. Resistivity anisotropy was in the range 0.2-1 at 300 K. Obtained geometry induced doping level corresponds to “effective impurity” concentration of 3x10 18 cm -3 . The dependence is in agreement with G-doping theory only below T=150K.