Energetic ion induced desorption of hydrogen from porous silicon studied by on line elastic recoil detection analysis
Abstract We report a detailed study on the concentration profiles and ion irradiation induced desorption of hydrogen from porous silicon (pSi) by on line elastic recoil detection analysis (ERDA) 100 MeV Ag ions have been employed to analyze the pSi samples prepared at different etching current densities. The observed blue shift in the photoluminescence of pSi with increase in etching current density is consistent with previous reports. Here we find that the concentration of hydrogen in near surface regions decreases with increase in etching current density. It is also observed that the concentration of hydrogen is greater in the near surface region and decreases rapidly as a function of depth in porous silicon. Further, the ion irradiation induced desorption of hydrogen from pSi has been characterized by the second order decay, indicating that the hydrogen desorbs in molecular form. The rate of desorption is found to be higher from the deeper layers when compared to that of near surface regions, possibly due to higher diffusivity of elemental hydrogen within the deeper layer. Strong electronic excitations produced by probing beam are expected to be responsible for the observed non thermal dissociation of Si H bonds and consequent desorption of hydrogen from the surface of pSi in molecular form. These results provide useful information to elucidate 1) the role of hydrogen in determining the optical properties of porous/nano crystalline silicon and 2) mechanisms that govern the non thermal dissociation of Si H bonds.