Fabrication of Porous Silicon as a Gas Sensor: The Role of Porous Silicon Surface Morphology

Abstract

Manufacture of an environmental polluting gas sensor with improved properties by controlling the preparation conditions of the photo-electrochemical etching technique (PECE). The amount of porosity, the diameter of the pores, and the thickness of the prepared layer of porous silicon (Psi) can be controlled by changing one or all of these conditions. In this paper, n-type Si with a crystalline orientation (100) was used, whereby PSi was prepared with the use of a red diode laser with a wavelength of 650 nm, using different radiation intensity, and with the constancy of etching time and current density. Through the results obtained, it was noted that: the porosity increases significantly up to 75% as well as the thickness of the PSi layer up to 1.45 µm with the increase in the intensity of the laser beam. Also, examining the morphology of the surface samples by field emission scanning electron microscope (FE-SEM) besides, the average pore diameters of the prepared samples were calculated. It is clear that the intensity of the laser beam used in the irradiation process is one of the important factors in determining the properties of the prepared PSi. PSi samples have been tested by FTIR to investigate chemical bonds on surfaces such as, (Si-Si, Si-H, Si-H2, Si-O-Si, Si-O-Si, Si-H, Si-O-Si). Samples tested as gas sensors and noticed that an increase in the sensing current to 5.3 µA has appeared with the increase of porosity value where methanol gas is used as background.