Pressure-induced contact resistance dominance in scanning spreading resistance microscopy of undoped InAs/GaSb heterostructure

This study examines the nature of current contrast formation and local transport mechanisms during scanning spreading resistance microscopy (SSRM) investigation of an undoped InAs/GaSb heterostructure. We demonstrate that in the high contact force regime (>100 nN), which is essential for stable visualization of layers on the cleaved cross section of the structure, an anomalous current signal distribution emerges. The current from GaSb layers significantly exceeds that from InAs layers. Based on a combination of SSRM data with numerical modeling of the carrier distribution within the layers, we demonstrate that the observed contrast is predominantly determined by contact resistance (Rc) rather than spreading resistance (Rs). This phenomenon is interpreted within a model in which the high local pressure at the nanocontact induces a compressively strained shell. This highly deformed region generates a high, steep potential barrier that suppresses interband electron tunneling at the diamond tip–InAs interface. Conversely, the GaSb valence band structure preserves a quasi-metallic hole transport path. Our results indicate the decisive role of tip-induced band structure modification during the nanoscale electrical characterization of narrow-gap materials.