We report a simultaneous strategy of impurity doping and crystal growth for building highly oriented Ge-doped α-Fe 2 O 3 nanosheet arrays vertically aligned on fluorine-doped tin oxide (FTO) glass substrates in hydrothermal environments, by using β-FeOOH nanorod arrays as sacrificial templates and highly reactive Ge colloidal solutions as dopant source. Microstructure characterization and elemental analysis reveal the preferential growth orientation, distribution of dopants, and doping level of Ge-doped α-Fe 2 O 3 nanosheet arrays. Based on the doping of Ge atoms, proper feature size of nanosheets (with thickness 2 O 3 nanosheet arrays show a photocurrent density of 1.4 mA cm −2 at 1.23 V vs. RHE, which is more than 50 times of the undoped α-Fe 2 O 3 nanorod arrays. Moreover, we find that the annealing temperature remarkably affects the majority carrier density and optical absorption efficiency, which enabled the determination of photocurrent density of hematite nanostructure arrays.