High quality boron-doped p-type freestanding diamond (FSD) films with smooth nucleation surface were prepared by hot filament chemical vapor deposition (HFCVD) method. The effects of B/C ratios on the electrical properties of FSD films were investigated by Hall effect measurement system. N-type Al-doped ZnO films were prepared on p-type FSD films by radio-frequency (RF) magnetron sputtering method to fabricate heterojunction. The I-V characteristic of the heterojunction was examined. The results showed a rectifying behavior of this structure.