We examine the surfaces and interfaces of GaN using ion beam analysis techniques in conjunction with chemical and electronic characterization methods. Following a description of Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), and cathodoluminescence (CL) spectroscopy, we illustrate the use of these methods to investigate GaN surfaces and interfaces intended for use in vertical p-i-n devices. For all cases, we quantify the depth-dependent crystallinity using a comparison of channeling and random RBS. For some cases, we also probe the geometry of atomic displacements using the angular-dependence of RBS yields, summed over the depths of interest. In addition, the depth-dependence of impurity incorporation and electronic states are probed using ERDA and CL in comparison with secondary ion mass spectroscopy and photoluminescence spectroscopy data. Finally, we compare and contrast GaN surfaces and interfaces prepared using epitaxy/etching/regrowth, ion implantation plus gyrotron annealing, and electric field-assisted diffusion, suggesting promising avenues for future investigations.