Thickness and film density of the deposited films were measured by X-ray reflectometry (XRR). GIXRD and XRR were measured with a PanAnalytical X'Pert Pro. Growth per cycle (GPC) values were calculated by dividing film thicknesses by the number of ALD cycles. Surface morphologies of the GaN films were studied using a high-resolution LEO 1550 Gemini field emission scanning electron microscope (SEM). The elemental compositions of the films were obtained using Rutherford backscattering spectrometry (RBS) and time-of-flight elastic recoil detection analyses (ToF-ERDA). The measurements were carried out in a 5-MV NEC-5SDH-2 pelletron tandem accelerator. 2 MeV 4 He + ions were employed for RBS and detected at a scattering angle of 170°. Two different geometries, azimuth angle 5°+tilt angle 2° and azimuth angle 40°+tilt angle 2°, were chosen to minimize channeling effects. In addition, more suppression of the probable channeling effects was undertaken by multiple small random-angular movements around the equilibrium angles within a range of 2°. RBS spectra were fitted by SIMNRA 7.02 code. Recoils, in ToF-ERDA, were detected at 45° angle between the primary beam and a ToF-E detector telescope in a gas ionization chamber (GIC) using a 36 MeV 127 I 8+ beam incident at 67.5° with respect to the sample surface normal. The ToF-E detector telescope consisted of two circular carbon foils with 8 and 5 µg/cm 2 thicknesses, 6 mm radius, a 0.05-msr solid angle (ΔΩ), and a flight distance of 425 mm between the foils. Utilizing a ToF-GIC setup provides the system with a good energy resolution and enhanced ion species separation in terms of mass and energy. 12 Average elemental compositions were also obtained from ToF-ERDA time-energy coincidence spectra using two different software packages, CONTES and Potku. Systematic uncertainties of the experiment, discussed in more detail elsewhere for light elements, were estimated to be a maximum of 5-10 %, whereas statistic uncertainties arisen from the number of experimental counts were ≤ 1.7 %. However, the relative elemental concentrations were obtained with higher accuracy. The stopping power data required for both RBS and ERDA simulations was retrieved from SRIM2013 code. Chemical composition and bonding states of the films were determined by an Axis Ultra DLD instrument from Kratos Analytical X-ray photoelectron spectroscopy (XPS) with a base pressure of 1.1×10 Torr (1.5×10 -7 Pa) and monochromatic Al Ka source (hυ=1486.6 eV). Depth profiling was carried out using an Ar ion sputter beam with an acceleration voltage, spot size, and sputtering time duration of 0.5 kV, 300×700 μm, and 300 s respectively. Spectra deconvolution and quantification were performed using Casa XPS software. During the peaks fitting, the C 1s peak at 285 eV was taken as a reference for all charge shift corrections.