Scanning tunneling spectroscopy of porous silicon in presence of methanol

In this research, we used the scanning tunneling spectroscopy (STS) technique to probe the local electrical properties of the surface of meso-porous silicon and its substrate, including local density of states (DOS) in air and in methanol environment to increase our knowledge of sensing phenomena. Meso-porous silicon was prepared on p+-type Si which has high sensitivity toward methanol. Observations revealed that while the surface electrical properties of p+-type Si have not sensible change toward methanol, average local density of state of the porous layer increases after the exposure to methanol especially in the E < EF region. Moreover, large number of surface states is produced in band gap which implies that the number of free-carriers in porous silicon increases in methanol environment. This phenomenon explains the change in electrical resistivity of meso-porous Si in the presence of methanol which is the base of organic gas sensitivity of this structure.