Surface structural, electronic and electrical properties of the quaternary alloy AlGaInN/GaN heterostructures are investigated. Surface termination, atomic arrangement, electronic and electrical properties of the (0001) surface and (10-11) Vdefect facets have been experimentally analyzed using various surface sensitive techniques including spectroscopy and microscopy. Moreover, the effect of sub-band gap (of the barrier layer) illumination on contact potential difference (VCPD) and the role of oxygen chemisorption have been studied.