Identifying the effect of point defects on tunneling in silicon tunneling devices

Many silicon devices, most prominently spin qubits of different flavors, rely on controlling electron tunnel rates, which are found to vary significantly from device to device. This is generally understood to result from material disorder, but the small length scales for electron tunneling in silicon (~ 10 nm) have made a direct characterization of these defects challenging. Scanning tunneling microscopy is a workhorse tool for understanding electronic structure on nm length scales, but has faced challenges in characterizing defects in silicon from the large background signal from dangling bonds, and the small signal originating near the silicon band gap. Fortunately, surface passivation and tip height adjustment has proven successful to enabling the spectroscopic identification of dopants through their effect on the band gap. Here, we employ those techniques to tunneling from the STM tip, through nominally intrinsic silicon, and into a shallow sub-surface layer of strongly doped silicon. This enables us to directly probe how defects in the intrinsic silicon layer influence tunneling.