Effect of a Patterned Sapphire Substrate on InGaN-Based p-i-n Ultraviolet Photodetectors

InGaN/GaN multi-quantum well (MQW) structures were used as an intrinsic semiconductor in InGaN-based p-i-n ultraviolet photodetectors (PDs). The cut-off wavelengths of the PDs grown on normal sapphire substrates (NSSs) and on patterned sapphire substrates (PSSs) were 445 and 450 nm, respectively, which is consistent with the photoluminescence emission wavelength. From the crystal and optical analyses, we found that the crystallinity and the absorption of the PDs grown on PSSs were superior to those of the PDs grown on NSSs. The maximum photoreactivities of the PDs grown on PSSs and on NSSs were 0.176 A/W and 0.109 A/W, respectively. In addition, the external quantum efficiencies of those PDs were 56.1% and 34.8%, respectively. From these results, we suggest that a PSS can play an important role in achieving a high reactivity and external quantum efficiency for InGaN-based PDs due to improved crystallinity and decreased optical absorption in the sapphire substrate.