Revealing inhomogeneous Si incorporation in GaN on nanometer scale by electrochemical etching

Typical methods of doping quantification are based on spectroscopy or conductivity measurements. The spatial dopant distribution assessment with nanometer-scale precision is limited usually to one or two dimensions. Here we demonstrate an approach to detect three-dimensional dopant homogeneity in GaN:Si layers using electrochemical etching (ECE). GaN:Si layers are grown by plasma-assisted molecular beam epitaxy. Dopant incorporation is uniform when the growth front morphology is atomically flat. Non-uniform Si incorporation into GaN is observed when step-bunches are present on the surface during epitaxy. In this study we show that local Si concentration in the area of step-bunch is about three times higher than in the area between step-bunches. ECE spatial resolution in our experiment is estimated to be about 50 nm. This makes ECE a simple and quantitative probing tool for local three-dimensional conductivity homogeneity assessment. Our study proves that ECE could be important both for fundamental studies of crystal growth physics and impurity incorporation and for ion-implanted structures and post-processing device control.