We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells.It is shown that only the doped sample shows electron cyclotron-resonance absorption.Also,the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra,and the doped one shows only one peak.The results reveal that the high concentration electrons accumulated in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other.The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field,and can cancel out a built-in electric field as observed in the undoped structures. We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe / BeTe / ZnSe type-II quantum wells. It is shown that only the doped sample shows electron cyclotron-resonance absorption. Als, the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra, and the doped one shows only one peak. The results reveal that the high concentration of electrons in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other. The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field, and can cancel out a built-in electric field as observed in the undoped structures.