AlGaN/GaN high electron mobility transistor (HEMT) structures are promising for high power and high speed electronic applications. The selection of a good buffer structure is crucial for the achievement of high quality HEMT devices. Here, we present a comparative analysis of structural, optical, and electrical properties of AlGaN/GAN HEMT structures with three different buffer configurations: step-graded AlGaN and superlattice-based buffers on Si, and no buffer on SiC substrates. The analysis of structural properties showed that the structure on SiC has better crystal quality. The Analysis also provided an insight of the role superlattice buffer to cut-off the dislocations and enhance the GaN channel crystallinity. Optical and electrical characterizations showed the enhanced 2DEG quality in the superlattice-based structure, due to the better stress management in the top layers. The electronic and optoelectronic quality of the structures were studied by fabricating HEMT and metal-semiconductor-metal photodetector devices. The devices analysis showed that the superlattice based structure outperformed the other two structures with drain current and transconductance of 406.3 mA/mm and 81.5 mS/mm, respectively, as well as photo-to-dark current ratio that is 2–3 orders of magnitude higher than the other two structures, under 325 nm light illumination. The results provide insights into the impact of different buffer configurations on the performance of AlGaN/GaN HEMT structures, suggesting that the superlattice buffer structure is the optimal choice for fabricating high-performance AlGaN/GaN HEMT-based electronics.