Resolving electronic inhomogeneity in CdZnTe bulk crystal via scanning microwave impedance microscopy

Local electronic imaging using a scanning microwave impedance microscope (MIM) is performed on as-grown CdZnTe bulk crystals at room temperature. Well-defined Te-rich secondary phase (SP) particles embedded in CdZnTe crystals are clearly observed in the MIM images. The high contrast observed via MIM is attributed to the discrepance between the dielectric response and conductivity of Te-SP particles and the CdZnTe matrix. A homogeneous phase structure is found within Te-SP particles according to the uniform MIM signal, which is further confirmed as the rhombohedral structure. The size effect of Te-SP on the response microwave intensity is discussed. It is demonstrated that the MIM signal is essentially independent of the domain sizes for Te-SP smaller than 10 µm. In contrast, for Te-SP larger than 10 µm, a roughly linear size dependence of the signal amplitude appears. In addition, the local area surrounding Te-SP is examined. A thin transition layer is observed surrounding the inclusion and is ascribed to Zn micro-segregation. For some Te-SP particles, a wide dark region surrounds the particle and is attributed to a high concentration of extended defects. For this Te-SP induced higher defect region, the microwave response is lower owing to the high electron relaxation polarization. Schematic diagram depicting the scanning microwave impedance microscope (MIM) configuration.