The isoelectronic doping in semiconductors is an effective method for improving device performance. Here we have investigated effects of isoelectronically Al-doped GaN buffer layer on optical and electrical properties of 365 nm InGaN/AlGaN ultraviolet light-emitting diodes (UV LEDs) grown by metal-organic chemical vapor deposition (MOCVD) on patterned sapphire substrate. In situ reflectance measurements revealed that the transition time from three-dimensional (3D) grain to step-flow two-dimensional (2D) coalesced growth mode was extended in the isoelectronically Al-doped GaN buffer layer as compared to undoped GaN buffer layer. The improved crystal quality, in terms of threading dislocation reduction, of the isoelectronically Al-doped GaN buffer layer was determined by cross sectional transmission electron microscopy studies and showed that the screw-type threading dislocation density was reduced. The light output power of UV LED was enhanced by 7.6% by incorporating optimum isoelectronic Al doping concentration in GaN buffer layer.