Herein, ammonium dihydrogen phosphate (NH₄H₂PO₄, ADP) crystals were grown in a defined crystallographic direction (θ = 90°, Φ = 45°) in an aqueous solution using the point seed rapid growth method. Ex situ atomic microscopy (AFM) measurements were implemented to observe the prismatic growth micro-morphology of ADP and Cr³⁺-doped ADP in the defined crystallographic direction. It was found that with the increasing supersaturation, the growth morphology changed in turn to elementary steps, macro steps, and 2D nuclei. Moreover, the differences between ADP and Cr³⁺-doped ADP grown in the defined crystallographic direction have been discussed. The influence of Cr³⁺ on the growth of ADP crystals has been explored.