Separate Absorption and Multiplication AlGaN Solar-Blind Avalanche Photodiodes With High-low-Doped and Heterostructured Charge Layer

In this work, an AlGaN solar-blind ultraviolet separate-absorption-and-multiplication avalanche photodiode is presented, where the charge layer has a high-low-doping (HLD) profile and a lower Al content. It was shown by numerical simulations that the HLD not only improved the transport efficiency of holes crossing the charge layer, but also enhanced the electric fields in the multiplication region. Moreover, a lower Al-content charge layer may induce a polarization effect to further increase the electric fields in the multiplication layers, promoting the impact ionization in the multiplication region and decreasing the avalanche breakdown voltage. The HLD and heterostructure employed in the charge layer can also improve the photoresponse by enhancing the electric field and inducing the upward valence-band bending.