Porous pyramidal silicon structures for improved light sensing performance

Abstract In this study, a highly sensitive and high-gain metal-semiconductor-metal photodetector was successfully fabricated based on textured silicon substrates. Texturing of silicon substrate is an efficient technique to control its surface reflectivity by increasing the specific surface area. A combination of porous and pyramidal structures of silicon was introduced to dramatically enhance the light-capturing ability and minimize the reflection coefficient of the silicon substrates. To fabricate pyramidal structures, selective chemical dissolution of silicon was carried out. To form porous structures on pyramidal silicon, electrochemical etching process with different etching time was followed. The morphology and structure of samples were characterized using field-emission scanning electron microscopy (FESEM) and X-ray diffractometry (XRD). The optical properties were investigated using Raman, photoluminescence (PL) and reflectance spectroscopy. Results indicated that the optical reflectivity can be minimized when an optimal etching time is applied which can be due to the enhancement in the exposed area and ability of light capturing. The enhanced porosity of the optimized substrate was illustrated by its elevated PL intensity. For studying the effect of porous layer on the optoelectrical properties of pyramidal structures, metal-semiconductor-metal (MSM) photodetectors were fabricated by deposition of Schottky contacts of Au on different samples. The device with the optimal porous layer exhibited enhanced sensitivity to the incident illumination due to the huge surface area and reduction in the reflection coefficient. Moreover, the ultrafast sensing behavior of this device reflects its improved optoelectrical performance in light detection.