The dataset includes data for the associated article, encompassing the scanning capacitance microscopy (SCM), scanning capacitance spectroscopy (SCS), and mercury CV data related to the GaN-based high electron mobility transistor (HEMT) structures. The SCM and SCS data were acquired using a Bruker Dimension Icon Pro AFM coupled with a Bruker SCM module, saved as '.spm' files viewable with Bruker's NanoScope Analysis software. The mercury CV data was obtained using a mercury probe capacitance-voltage measurement system from Materials Development Corporation, stored as a text file importable to data analysis software like Origin.