ANODIC-OXIDATION OF P-TYPE AND P(-TYPE POROUS SILICON - SURFACE STRUCTURAL TRANSFORMATIONS AND OXIDE FORMATION())

The transformations induced by the anodic oxidation process on the por e structure and surface states of p-type and p(+)-type porous silicon have been studied by Rutherford backscattering spectroscopy, local vib rational mode and electron paramagnetic resonance spectroscopy. Surpri singly the anodic oxidation does not lead to a significant formation o f silicon oxide in p-type layers; the oxygen is mainly incorporated in silicon back-bonded configurations without perturbation of the initia l H surface passivation. On the contrary, in p(+)-type samples, a unif orm oxide layer of a thickness up to 45 Angstrom is formed from the ve ry first stages of anodic oxidation. The influence and correlations be tween the surface structure and the PL efficiency are discussed.