Direct observation of spatial distribution of carrier localization sites in ultrathin GaN/AlN quantum wells by spreading resistance microscopy
Spreading resistance microscopy (SRM) was used to study nanoscale variations in electronic and structural properties of an ultrathin near-surface GaN/AlN quantum well (QW). In the SRM images of the growth surface of the GaN/AlN QW heterostructure, an inhomogeneous current contrast was detected in the form of disk-like regions of increased conductivity with the sizes in the range of 50–160 nm and a density of ∼1.7 × 109 cm−2. Analysis of the current contrast dependence on the polarity of the sample dc bias and the growth surface morphology revealed that these regions are the GaN islands of various thicknesses. These islands spread predominantly within the crystal grains rather than along their boundaries and represent electron localization sites in the QW plane. The results demonstrate the applicability of SRM as an express and non-destructive technique to delineate quantitatively in-plane fluctuations in the electronic and structural properties of near-surface GaN/AlN QWs with a high spatial resolution of ∼10 nm.
This work was supported in part by RFBR-BRICS (#17-52-80089).