Influence of the number of growth cycles on the solar-blind photoresponse of amorphous and crystalline Ga₂O₃ films by atomic layer deposition

This study investigates the photodetection performance of amorphous Ga 2 O 3 and crystalline films grown by atomic layer deposition with varying growth cycles (1000–7000 cycles). The fundamental difference in structural order – long-range in crystalline versus short-range in amorphous - governs their distinct optoelectronic behaviors. For amorphous Ga 2 O 3 devices, photocurrent/responsivity nealrly saturates beyond a certain thickness. This limitation comes from low carrier mobility and short diffusion length due to abundant trap states. In contrast, crystalline Ga 2 O 3 photodetectors show a monotonic increase in responsivity with film thickness, benefiting from its long-range order which contributes to a longer carrier diffusion length and superior charge collection efficiency. Consequently, for thinner films, the high photoconductive gain from carrier trapping in amorphous films leads to higher responsivity for amorphous Ga 2 O 3 photodetecors. However, for thicker films, the photoresponsivity and response speed of crystalline Ga 2 O 3 photodetectors are both superior to those of amorphous Ga 2 O 3 photodetectors. These advantages can be attributed to the greater absorption depth and longer carrier diffusion length. This work establishes how the material phase (amorphous vs. crystalline) and film thickness jointly influence the performance of Ga 2 O 3 photodetectors. The obtained results provide valuable insights for the design of Ga 2 O 3 photodetectors. • Saturation of the photoresponsivity in amorphous Ga 2 O 3 is observed for the first time as the film thickness increases. • The photoresponsivity of crystalline Ga 2 O 3 PDs increases monotonically as a function of the number of growth cycles. • A parallel comparison of amorphous and crystalline Ga 2 O 3 PDs is provided across a wide range of ALD cycles.