Direct Measurement of Individual Deep Traps in Single Silicon Nanowires

The potential of the metal nanocatalyst to contaminate vapor-liquid-solid (VLS) grown semiconductor nanowires has been a long-standing concern, since the most common catalyst material, Au, is known to induce deep gap states in several semiconductors. Here we use Kelvin probe force microscopy to image individual deep acceptor type trapping centers in single undoped Si nanowires grown with an Au catalyst. The switching between occupied and empty trap states is reversibly controlled by the back-gate potential in a nanowire transistor. The trap energy level, i.e., E-C - E-T = 0.65 +/- 0.1 eV was extracted and the concentration was estimated to be similar to 2 x 10(16) cm(-3). The energy and concentration are consistent with traps resulting from the unintentional incorporation of Au atoms during the VLS growth.