Conductive atomic force microscopy has been used to study both the topography and electronic properties of 30nm scale ErAs islands grown by molecular beam epitaxy (MBE) on n-type GaAs substrate. A calibration method was realized to determine the growth rate of the ErAs so that we can control the size of the ErAs islands. Current flow images and surface profile around ErAs islands were simultaneously measured for local conductive distribution corresponding to real space profile, where the correlations are revealed. The conductance on ErAs islands is found to be larger than that on the GaAs buffer layer from I-V characteristics via voltage sweeping from negative to positive voltage. The I-V curve and resistance of the tunnel junction with ErAs were evaluated. It exhibits that less voltage loss can be achieved even higher than 1000 suns.