Measurements of Electrostatic Potential Across p--n Junctions on Oxidized Si Surfaces by Scanning Multimode Tunneling Spectroscopy

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We investigated the variation in contact potential difference (CPD) voltage across p--n junctions on oxygen-passivated Si(110) surfaces by scanning multimode tunneling spectroscopy, which detects probe--sample interaction force simultaneously with tunneling current. The enhancement of sensitivity to electrostatic force was achieved with a small amplitude of probe vibration (0.3 nm) when the tip--sample gap was adjusted to reduce short-range interactions by maintaining the tunneling current at a specified bias voltage. At the optimal tip--sample gap, the CPD voltage, derived from force gradient spectra, agrees with the expected built-in potential across the p--n junction. The CPD voltage showed a standard deviation of ${\sim}30$ mV on atomically flat terraces. Larger fluctuations were ascribed to structural and charge variations on the oxidized surfaces.
2011-04-25