The photonics world is becoming increasingly interested in plasmonic photodetectors. The field of plasmonics allows light to be dedicated into small spaces in metallic structures, and this property has the ability to simulate extra improvements in performance of photodetectors. In this work it is presented gold (Au) and Aluminum (Al) surface plasmon polariton (SPP) GaAs PIN photodetector achieved higher internal quantum efficiency (IQE), as the IQE with Au and Al SPP rectangle grating is 95.01%, while the IQE with Au SPP rectangle grating is 85%, which indicates an improvement of 10.01%. It is also presented nanograting various shapes such as triangular, ellipse, bowtie and circle, and investigate its impact on improving the performance of the proposed photodetector. The internal quantum efficiency is improved to 98.48% with a total enhancement IQE of 13.48%. Moreover, output current and responsivity are improved. This remarkable enhancement is achieved with bowtie grating as compared to other shapes and previous published papers.