A comprehensive model for the electrical nanocontact on germanium for scanning spreading resistance microscopy applications

Abstract

Quantitative carrier profiling represents a key element in the process development of future nanoelectronic devices. During the last decade, scanning spreading resistance microscopy (SSRM) has evolved as the method of choice for two-dimensional carrier mapping due to its unique spatial resolution and high sensitivity when applied to silicon (Si)-based devices. While the electrical nanocontact between a SSRM probe and Si is well documented, the insight is insufficient to understand or make predictions about the properties of the SSRM contact in case of high-mobility germanium (Ge) samples. Therefore, we present in this paper a model describing this contact in more detail, taking into account the effects of the applied pressure as this leads to the formation of a β-Sn pocket right underneath the probe and a spatially non-homogeneous bandgap reduction in the underlying Ge. The resistance probed through the resulting Schottky contact is further influenced by the dimensions of the nanocontact and in particular by the spatial extent of the surface states which are present at the cross-sectional surface. To account for the low-bias IV-characteristics of n-Ge, the model also includes trap-assisted tunneling. Using this model, we are able to describe the role of probe properties such as probe radius and resistivity on the shape (steepness, saturation, non-linearity) of the Ge calibration curve. We demonstrate experimentally and by simulation that low-resistivity probes are indispensable for a high sensitivity when applying SSRM to highly doped samples.

Suppression of boron incorporation at the early growth phases of boron‐doped diamond thin films

“…The presence of residual O during the early growth phases of B‐doped diamond thin films via chemical vapour deposition (CVD) can be detrimental regarding the electrical properties of the diamond film, which, in turn, will impact nanoscopic diamond tips and electrode application . This is due to the interaction of O with the B‐containing gas by converting the B‐precursors into energetically stable B–O species, which are not incorporated into the diamond film.…”

Scanning spreading resistance microscopy for electrical characterization of diamond interfacial layers

“…The latter represents the local spreading resistance underneath the tip which is directly linked to the local conductivity of the diamond material . Although the use of a metallic tip for such measurements is an obvious choice and we have demonstrated TiN tips for the SSRM analysis on Ge samples , they suffer from rapid wear when scanning on diamond surfaces. For the experiments in this work only diamond‐based tips are hard enough for successfully probing boron‐doped diamond interfaces.…”

“…SSRM is based on atomic force microscopy (AFM) and is the leading method for quantitative 2D‐carrier profiling, featuring ∼1 nm spatial resolution, a response function covering a wide dynamic range of carrier concentration and the capability for site‐specific analysis . SSRM has been demonstrated as a unique concept for the electrical characterization of semiconductor devices with successful applications toward silicon‐based metal‐oxide semiconductor field‐effect transistors (MOSFETs) , FinFETs , nanowire‐based transistors , and Ge‐based p‐MOSFET devices .…”

Resolving ZnO-based coaxial core-multishell heterostructure by electrical scanning probe microscopy

“…25 In practice, a stable electrical contact between the tip and the sample is critical to achieving reliable resistance recording, which is usually implemented by applying a relatively large contact-force of the AFM tip on the sample. 26 In the case of silicon, a force larger than 15 lN is needed for the probe to penetrate the native oxide layer on top of the silicon surface. 25 Nevertheless, we found that a much lower force is enough for ZnO to obtain stable results of SSRM owing to its relative softness (Mohs hardness: 4.5 for ZnO versus 7 for silicon) and the absence of the insulating top layer.…”

“…determined by the effective radius of the tip-sample contact, which can be significantly smaller than that of the tip, whereas the spatial resolution of SCM depends determinedly on the entire volume of the depletion region in response to the modulating voltage, which can far exceed the dimension of the tip. 24,26 A profile of SSRM resistance along the line across a NW in Fig. 4(b) is plotted in Fig.…”