Heterojunction photodiodes consisting of n-TiO2/p-Si were produced using the ALD method on a single-sided polished p-type Si wafer. The characteristics of the Al/TiO2/Si/Al heterojunction device were assessed through current–voltage (I-V) measurements. The ideality factor (n) and barrier height ( (Formula presented) ϕbin ) were identified as 4.6 and 0.64 eV, respectively. To gain deeper insights into the light-detecting characteristics of the photodiode, investigations on photosensitivity (K), responsivity (R), specific detectivity (*D) and noise equivalent power (NEP) were conducted based on the correlation between photocurrent and light intensity. The photo-response efficiency was evaluated through transient photocurrent (I-t) assessments across varying light power levels. The I-V curve examination under various illumination sources revealed that the photodiode’s responsiveness increased as the TiO2 thickness decreased. The impact on the characteristic capabilities of the n-TiO2/p-Si heterostructure as the TiO2 film thickness increased was scrutinized in relation to layer resistance and structural defect states. Consistent results were obtained through experimental investigations, with comparative analyses conducted between theoretical and experimental data to validate the findings.