A deep understanding of semiconductors-dielectrics interface properties will provide guidelines to optimize efficient passivation solutions for InGaN/GaN based μLED. To this end, the quantum wells (QW) semiconductor is of tremendous interest since a lot of surface recombinations are likely to occur at LED active regions edges and are probably responsible for the low μLED efficiencies. Thus we discuss in this paper about X-ray photoemission (XPS) and wavelength dispersive X-ray fluorescence (WDXRF) characterizations of In<sub>0.1</sub>Ga<sub>0.9</sub>N surfaces after acid, basic or sulfur based chemical treatments followed or not by atomic layer deposition (ALD) of Al<sub>2</sub>O<sub>3</sub> thin films with TMA/H<sub>2</sub>O or TMA/O<sub>2</sub> plasma (plasma enhanced ALD) at 250°C. Depending on chemical treatments, variations of indium related XPS peaks were observed, which did not seem to be significantly affected by deposition of Al<sub>2</sub>O<sub>3</sub> whatever the oxidizing precursor. The extreme surface concentration of indium was probably reduced, suggesting that some chemical pre-treatments for cleaning or passivation steps would have a direct impact on InGaN QW properties at LED edges. After sulfur based chemical treatments, even if sulfur was hardly detected by XPS, complementary measurements by WDXRF and subsequent calibration of the sulfur signal supported evaluation of a low surface concentration of sulfur. Changes of Al<sub>2</sub>O<sub>3</sub> related XPS peaks suggested that the various studied pre-treatments induced different nucleations of first ALD cycles. Then, a clear variation of InGaN surfaces hydrolysis depending on surface treatments was finally highlighted by WDXRF based counting measurements, opening the way to a better understanding of first Al<sub>2</sub>O<sub>3</sub> layers nucleation on InGaN.