A Scanning Microwave Microscopy Study of FIB-Induced Local S₁₁ Response Changes in InGaAs/InP and HfO₂/InGaAs/InP...

In this work, scanning microwave microscopy (SMM) is used to monitor the evolution of the local microwave response, in terms of variations in the S₁₁ input reflection coefficient, in two III-V heterostructures relevant to mid-infrared photonics, namely a 150 nm thick heavily doped InGaAs layer on InP and HfO₂ (35 nm)/InGaAs (150 nm)/InP, subjected to Ga⁺ FIB milling over a broad dose range. By correlating raw, uncalibrated two-dimensional S₁₁ maps with atomic force microscopy (AFM) and Raman spectroscopy, we observe a dose-dependent evolution from implantation-dominated behavior to progressive amorphization, layer thinning and surface roughening. In the uncapped InGaAs/InP system, the SMM response varies monotonically with ion dose, consistent with progressive FIB-induced modification of the exposed InGaAs layer and, at larger milling depths, of the underlying InP substrate. In the HfO₂-capped structure, the microwave response is more complex: the oxide initially acts as a partial buffer against ion penetration, delaying damage transfer, but this effect progressively weakens as the cap is thinned and structurally degraded. The resulting S₁₁ contrast may reflect the combined effects of FIB-induced structural modifications, layer removal, local material composition, and surface morphology. Overall, the combined dataset indicates that SMM is a potentially highly sensitive probe of FIB-induced nanoscale modifications in the local microwave response, especially at low doses, provided that suitable on-chip calibration and de-embedding structures are available.