Dispersive RF Measurement of a Tip Induced Quantum Dot in a mK-STM

The development of device-based semiconductor spin qubits is an inherently challenging, multi-faceted effort. Such an endeavor requires significant materials overhead coupled with complex, multi-layered fabrication processes before any measurement can even take place. This workflow is further complicated when exploring new materials with the goal of determining suitability for implementation in devices. Here, we seek to circumvent the barriers imposed by device fabrication and instead probe semiconducting materials directly via radio frequency (RF) reflectometry combined with a millikelvin scanning tunneling microscope (mK-STM). In this configuration, STM tip induced band bending gives rise to the formation of a quantum dot which can be scanned across a sample surface as a means to study interactions with surrounding defects. Meanwhile, the dispersive RF measurement provided by an integrated LC-tank circuit permits the determination of specific dot properties, including charge occupation and size. As a demonstration of this capability, we present spectroscopic measurements on chlorine-terminated silicon wafers of various doping levels, in which the STM tip-sample bias is swept while small shifts in the tank circuit resonance, due to changes in quantum capacitance, are recorded. The techniques described herein will be extended to more complicated heterostructure materials, while also providing a pathway for non-destructive characterization of semiconductor materials for quantum information science applications.