Microwave microscopy of diamond semiconductor structures

A scanning near-field microwave microscope (SNMM) was used to study resistance Rsh of a boron delta-doped epilayer of diamond grown on a high pressure and high temperature substrate. Measurements were performed with an ∼1.4 GHz working frequency and an ∼85 μm space resolution microscope on samples with a lateral dimension of 3 × 3 mm2. Some substrates featured a crystalline structure defect over which the epilayer resistance Rsh was seen to increase by more than an order of ∼1 mm linear dimensions of the high-ohmic region. The SNMM measurement data revealed some substrates to have nonuniform conductivity, i.e., a high-ohmic area in the central part surrounded by a conducting edge region. In the latter case, the SNMM method allowed determining a surface distribution of epilayer resistance Rsh, undistorted by the shunting influence of the substrate. The reliability of the SNMM results is confirmed by the local four-probe resistance measurements. At the same time, the alternative methods such as the non-local van der Pauw method and secondary ion mass spectroscopy failed to detect the nonuniformity of the structure conducting properties, established by SNMM. The obtained values for a hole concentration of Np ≈ 1.7 × 1020 cm−3 and a mobility of μH ≈ 15 cm2/(V s) are assumed to possibly pertain to the diamond delta-layer.