The authors have investigated the electron transport properties of Zn1-xMnxO/ZnO modulation-doped heterostructures grown on ZnO (0001) single-crystal substrates. By varying the growth temperature (T-g) of ZnO and Zn1-xMnxO layers, the growth mode changes from three-dimensional grain growth to two-dimensional growth. In this study, Zn0.88Mn0.12O/ZnO heterostructures with different growth modes of the Zn0.88Mn0.12O barrier layer were fabricated by deposition at different T-g. The effect of the growth mode of the Zn0.88Mn0.12O barrier layer on carrier confinement at the Zn0.88Mn0.12O/ZnO heterointerface is discussed.