We report a study of the surface of Al-Al2O3-Au light-emitting junctions deposited on CaF2 underlayers of 100 nm thickness with scanning tunnelling micos-copy (STM) in air. For the first time, two kinds of the noughness on the junction surface are obserned, which have the transverse correlation length of 30-70nm and 3-5nm, respectively. The smaller one is modulated by the larger one. The existanoe of this surface roughness with the transverse correlation length of 3-5 nm is in agreement with the theoretical predication of Lake and Mills