Low temperature electrostatic force microscopy of a deep two-dimensional electron gas using a quartz tuning fork

Using an ultralow temperature, high magnetic field scanning probe microscope, we have measured electric potentials of a deeply buried two-dimensional electron gas (2DEG). Relying on the capacitive coupling between the 2DEG and a resonant tip/cantilever structure, we can extract electrostatic potential information of the 2DEG from the dynamics of the oscillator. We present measurements using a quartz tuning fork oscillator and a 2DEG with a cleaved edge overgrowth structure. The sensitivity of the quartz tuning fork as force sensor is demonstrated by observation of Shubnikov-de Haas oscillations at a large tip-2DEG separation distance of more than 500 nm.